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Proceeding of Geotechnical Issues and Practices

on Deltaic Deposits and Highly Compressible Soils

Seoul 2017 19th

ICSMGE Seoul 2017

19th International Conference on Soil Mechanics and Geotechnical Engineering

17 – 22 September 2017/COEX, Seoul, Korea

Technical Committee ATC7 – Thick Deltaic Deposits

Schedule / Location Sep. 21, 11:00~12:30 / Hall E1

>>Proceeding of Geotechnical Issues and Practices

on Deltaic Deposits and Highly Compressible Soils

Organizers ATC7 – Thick Deltaic Deposits

Organizing Committee

∙Chair Person Jin Man Kim, Pusan Natioanl University, Korea

∙Vice Chair Yun Tae Kim, Pukyung National University, Korea

∙Secretaries

Tae Hyung Kim, Korea Maritime and Ocean University, Korea

Jae Hun Ahn, Pusan Natioanl University, Korea

∙International Representatives Du Hwoe Jung, Pukyung National University, Korea

Mamoru Miura, Kyoto University, Japan

Shui Long Shen, Shanghai Jiao Tong University, China

Sergey Kudrjvzev, Fare East Russia Transport University, Russia

∙Core Members Kwang Yeol Lee, Dongseo University, Korea

Shui Long Shen, Shanghai Jiao Tong University, China

Mamoru Miura, Kyoto University, Japan

Yan Jun Du, Southeast University, China

Nam Jae Yoo, Kangwon National University, Korea

Woo Jin Lee, Korea University Korea,

Du Hwoe Jung, Pukyung National University, Korea,

Jin Man Kim, Pusan Natioanl University, Korea

Sang Soo Jeon, Inje University, Korea

Tae Hyung Kim, Korea Maritime and Ocean University, Korea

Sergey Kudrjvzev, Fare East Russia Transport University, Russia

J. C. Chai, Saga University, Japan

Ling Hoe, Columbia University, USA

M.S. Mohan Kumar, Indian Institute of Science, India

Song Yu Liu, Southeast University, China

Xiao Wu Tang, Zhejiang University, China

Jae Hun Ahn, Pusan National University, Korea Achmad Wicaksono, Brawijaya University, Indonisia

Hukada Naozo, Fukken Company, Japan

Hasegava Akira, Hachinihe Institute of Technology, Japan

Mangushev Rashid, Saint-Petersburg State Architectural and Civil Engineering Univ,. Russia

Chan Dave, University of Alberta, Canada

Vinnikov Juri, Polrava Techical University, Ukraine

Leung Chun Fai, National University of Singapore, Singapore

Der Wen Chang, Tamkang University, Taipei, China

Albert Ho, Arup Co., Hong Kong, China

M. Mets, President of Geotechnical Society of Estonia

Koichi Nakagawa, Osaka City University, Japan

Vera-Grunauer Xavier, Catholic University, Equador

∙Charter Members Sang Kyu Kim, Former Vice President of ISSMGE, Korea

Seung Ryul Kim, ESCO Consultant, Korea

Kwang Yeol Lee, Dongseo University, Korea

Young Nam Lee, Hyundae Construction., Korea

Sung Gyo Chung, Dong-A University, Korea

Byung Hee Kang, Inha University, Korea

Norihiko Miura, Saga University, Japan

Koichi Nakagawa, Osaka City University, Japan,

Chan Ho Park, Dohwa Consultants, Korea

Young Mok Park, Yungnam University, Korea

H. Tanaka, Port and Harbor Research Institute, Japan

∙Advisory Committee M. R. Madhav, Former Vice President of ISSMGE, Indian Institute of Technology, Kanpur, India

Sang Kyu Kim, Former Vice President of ISSMGE, Retired

Askar Zhussupbekov, Vice President of ISSMGE, L.N. Gumilyov Eurasian National University, Kazahstan

Nam Jae Yoo, Former Chair of ATC-7(2009-2010), Kangwon Natioanl University, Korea

Kwang Yeol Lee, Former Chair of ATC-7(2011-2016), Dongseo University, Korea

Norihiko Miura, Former Chair of ISLT, Saga University, Japan

Heinz Bradl, President of Austrian Member Society of ISSMGE, Wien, Austria

Edyta Malinowska, Warsaw University of Life Sciences, Warsaw, Poland

Jozsef Mecsi, President of Hungarian Geotechnical Society, Bubapest, Hungary

Jana Frankovska, President of Czeck and Slovak Geotechnical Society, Bratislava, Slovakia

Tadatsugu Tanaka, University of Tokyo, Japan

Tanaka, H., Port and Harbor Research Institute, Japan

D. T. Bergado, Asian Institute of Technology, Thailand

>>Preface

ISSMGE Asian Technical Committee 7 (ATC 7) aimed at promoting and enhancing

professional activities focusing on the geotechnical issues on thick deltaic deposits.

Thick soft clay deposits exist everywhere in the world. Many developed countries

get short of the lands for urban and industrial developments; the use of clay deposits

has increased remarkably. Thick deposits of soft soils may invoke many geotechnical

problems during construction in urbanization. In deltaic areas, thick clay deposits

have been problematic during urban and industrial developments, and therefore

attracted attentions from civil engineers with huge challenges. Notable examples of

the challenges faced in civil and geotechnical engineering include: large settlement

of the Kansai International Airport, subsidence of Bangkok city, reclamation works

in Singapore, and geotechnical issues in the thick deltaic deposits.

ATC 7 aims to promote and enhance the professional activities in geotechnical

engineering related to depositional history and environments, engineering

properties, and foundation problems on thick deltaic deposits. ATC 7 developed a

website for communication and information exchange. The website can be accessed

through the link https://sites.google.com/site/atc7issmge/home.

ATC 7 members are honored to have all the distinguished friends and guests from

USA, India, Taiwan, Japan, Kazakhstan, Slovakia and Korea who are dedicated to

this workshop. We hope that this workshop will play a key role for realizing our goals

and encourage collaborative research works.

https://sites.google.com/site/atc7issmge/home

>>Venue

>>Schedule

Sep. 21, 11:00~12:30 / Hall E1 (Parallel Session 6)

>>Program

Sep. 21, 11:00~12:30 / Hall E1 (Parallel Session 6)

1. Oral presentation

11:10~11:20 Failure of Stone Columns and Means of Rectification for Tank Foundations over Soft Soil Deposit

Kaushik Bandyopadhyay, Jadavpur University, India

1

11:20~11:30 Feasibility of ion exchange membranes to control pH changes during electro-osmotic consolidation of soft soils

Jay N. Meegoda, New Jersey Institute of Technology, United State

5

11:30~11:40 MSW-leachate-soil-interactions and its effect on shear parameters using admixture

M.V. Shah, Lalbhai Dalpatbhai College of Enginnering, India

9

11:40~11:50 Mechanism of subsidence from pore pressure flctuation in aquifer layers

An-Bin Hueng, National Cheng Kung University, Taiwan

13

11:50~12:00 Evaluation of the bearing capacity of suction bucket foundations used for offshore wind turbines using finite element modeling

Pouyan Bagheri, Pusan National University, Korea

17

12:00~12:10 Consolidation Properties of Soft Clay Mixed with Useful Microorganisms and Application of Simple Dehydration Method

Kiyoshi Omine, Nagasaki University, Japan

21

12:10~12:20 Consideration of Induced Overconsolidation on Response of Granular Pile Reinforced Soft Ground – Effect of Overconsolidation Ratio

Kandru Suresh, CMRCET, India

25

12:20~12:30 Discussion

2. Poster section

Efficiency of improvement methods in compressible soil based on the results of geotechnical monitoring

Jana Frankovská, Slovak University of Technology, Slovakia

Quality Control of Cement-Improved Soil Monika Súl’ovská, Slovak U University of Technology, Slovakia

New effective construction management of the soft ground improvement

Tae-Hyung Kim, Korea Maritime and Ocean University, Korea

An Analysis Model of PDV-installed Deposit Consolidation Considering Varied Discharge Capacity with Depth

Ba-Phu Nguyen, Pukyung National University, Korea

Determination of bearing pressure of soil at the Abu-Dhabi Plaza construction site in Astana by a plate load test

Askar Zhussupbekov, L.N. Gumilyov Eurasian Natioanl Unversity, Kazakhstan

Offered methods for the determination of bearing capacity of pile regarding types of foundation of Astana city

N.T. Alibekova, L.N. Gumilyov Eurasian Natioanl Unversity, Kazakhstan

>>Contents

Oral presentation

Failure of Stone Columns and Means of Rectification for Tank Foundations over Soft Soil Deposit ..... 1

K. Bandyopadhyay, S. Saraswati and S. Bhattacharjee Feasibility of ion exchange membranes to control pH changes during electro-osmotic consolidation of soft soils ................ 5

L. Martin and Jay N. Meegoda MSW-leachate-soil-interactions and its effect on shear parameters using admixture ........................ 9 M.V. Shah and Jerome Jose Mechanism of subsidence from pore pressure fluctuation in aquifer layers ................................... 13

Wen-Jong Chang, Shih-Hsun Chou and An-Bin Huang Evaluation of the bearing capacity of suction bucket foundations used for offshore wind turbines using finite element modeling .................................................................................................... 17

Pouyan Bagheri, Su Won Son and Jin Man Kim Consolidation Properties of Soft Clay Mixed with Useful Microorganisms and Application of Simple Dehydration Method .................................................................................................................... 21 Kiyoshi Omine and Satoshi Sugimoto Consideration of Induced Overconsolidation on Response of Granular Pile Reinforced Soft Ground – Effect of Overconsolidation Ratio ................................................................................................. 25 K. Suresh , M.R. Madhav, E. C. Nirmala Peter

Poster presentation Efficiency of improvement methods in compressible soil based on the results of geotechnical monitoring .................................................................................................................................. 31 Jana Frankovská, Miloslav Kopecký, Peter MuŠec and Viktor Janták Quality Control of Cement-Improved Soil ...................................................................................... 35 Monika Súľovská, Peter Turček and Zuzana Štefunková New effective construction management of the soft ground improvement ..................................... 39 Tae-Hyung Kim, Eun-Sang Im, Kwang-Yeol Lee, Chang-Hoon Jung and Chang-Ho Kim An Analytical Model of PVD-Installed Deposit Consolidation Considering Varied Discharge Capacity with Depth .................................................................................................................................. 42 Ba-Phu Nguyen and Yun-Tae Kim Determination of bearing pressure of soil at the Abu-Dhabi Plaza construction site in Astana by a plate load test ............................................................................................................................. 45 Askar Zhussupbekov, Abdulla Omarov, Ivan Morev, Gyulnara Zhukenova, Gulzhanat Tanyrbergenova Offered methods for the determination of bearing capacity of pile regarding types of foundation of Astana city .................................................................................................................................. 48 A.Zh.Zhussupbekov, N.T.Alibekova, A.S.Tulebekova & N.A.Toleubay, Zh.N.Ospanova, N.N.Satan, D.Khussainova

1.Oral session

Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017

Failure of Stone Columns and Means of Rectification for Tank Foundations over Soft Soil Deposit

Échec des colonnes de pierre et des moyens de rectification pour les fondations de réservoirs au-dessus du dépôt de sol mou Kaushik Bandyopadhyay & Subhajit Saraswati Professor, Construction Engineering Department, Jadavpur University, India, email: [email protected]; [email protected]. Sunanda Bhattacharjee

Project Manager, Mackintosh Burn Ltd, India

ABSTRACT: At a site near the coastal region of West Bengal, India soft soil was encountered upto great depths. The deposit resembled more or less like marine clay one with standard penetration (SPT) values ranging from 2 to 6 upto 28.00m depth below the ground level. The deposit mainly consisted of soft to very soft grey silty clay / clayey silt with varying percentage of decomposed vegetation and laminated silt. Three numbers of water storage tanks of diameter 30.0m and height 14.50m were constructed at the site. Ground improvement technique by installation of stone columns upto the depth of 10.00m was adopted. It was observed that total and differential settlements to the tune of 802mm and 141mm respectively had occurred within one year of installation of the tanks. Besides, the settlements have been continuing unabated till date. It is believed that the scheme of stone columns was not adequate to arrest the settlements. Three more borings are recently made upto the depth of 50.00m below the ground level to investigate the problem and acquire sufficient data regarding primary and secondary consolidation. This paper presents a detailed discussion on the causes of failure based on field and laboratory results and suggests some remedial measures to arrest settlement.

RÉSUMÉ: Dans un site proche de la région côtière du Bengale occidental, l'Inde a rencontré des sols mous jusqu'à des profondeurs très importantes. Le dépôt ressemblait plus ou moins à de l'argile marine avec des valeurs de pénétration standard (SPT) allant de 2 à 6 jusqu'à 28,00 m de profondeur au-dessous du niveau du sol. Le dépôt consistait principalement en du limon argileux / argilo-silt gris mous à très doux avec un pourcentage variable de végétation décomposée et de limon stratifié. Trois réservoirs de stockage d'eau de 30,0 m de diamètre et 14,50 m de hauteur ont été construits sur le site. La technique d'amélioration du sol par l'installation de colonnes de pierre jusqu'à la profondeur de 10.00m a été adoptée. Il a été observé que des règlements totaux et différentiels de 802 mm et 141 mm respectivement se sont produits dans l'année suivant l'installation des citernes. En outre, les colonies se sont poursuivies sans relâche jusqu'à ce jour. On croit que le système des colonnes de pierre n'était pas adéquat pour arrêter les colonies. Trois autres forages ont été réalisés récemment jusqu'à la profondeur de 50,00 m sous le niveau du sol pour étudier le problème et acquérir des données suffisantes concernant la consolidation primaire et secondaire. Cet article présente une discussion détaillée sur les causes de l'échec basée sur les résultats de terrain et de laboratoire et suggère quelques mesures correctives pour arrêter le règlement.

KEYWORDS: Marine clay, settlement, stone columns, failure, remedy.

1 INTRODUCTION

In coastal regions of West Bengal, India, 30 to 40% of its area is characterized as soft saturated silty clay upto great depth. This soft soil exists along the alluvial plain of Gangetic West Bengal. Different plants and industry are situated along this region. Generally large scale ground improvement techniques are adopted at such locations e.g, installation of sand drain or PVD (Jansen et al. 1983), gypsum lime column (Halkola 1983), cement grouting (Mittal 2015), inclusion of rubber tyre powders (Khabiri et al. 2016) and use of geotextile (Babu 2006). Stone column has been widely applied internationally as a successful sustainable and efficient technique for improving the load bearing capacity and controlling the settlement of oil or water tank foundation constructed over soft soil and in many cases considered as an economical alternative to deep foundation. Here in the present case under consideration it is observed that within one year of commissioning of fire water tank having its foundation reinforced with stone column, substantial differential settlement has occurred and is still continuing. Extensive research with regard to different field and laboratory studies are carried out to investigate the cause of failure. The present work is an attempt to evaluate the alternative methods for remedial measures, too.

1.1 Objective of present study

The objective of the present study may be summarized as given below:

a) Identification of the sub-soil profile. b) Determination of the soil design parameters. c) Estimation of present and future state of settlement. d) Remedial Measure and Recommendation.

1.2 Scope of work

The scope of investigation work consisted of carrying out subsoil investigation at site and assessment of settlement. The second step was different laboratory investigations. The first step of sub-soil investigation work was broadly separated into the following activities.

a) Sinking of Boreholes. b) Carrying out in-situ tests like Standard Penetration

Test. c) Collection of disturbed and undisturbed soil samples. d) Carrying out laboratory tests. e) Estimation of total and differential settlement under

tank foundation based on full water loading in tanks. f) Assessment of further settlement with respect to

available time based on present consolidation status.

1


g) Suggestion of Remedial Measure and Recommendation.

The second step of laboratory investigation was carried out to ascertain the various engineering properties of the subsoil as per relevant Indian Standard Codes (SP36 Part1 1987 & SP36 Part 2 1988).

The site has been investigated with the help of three numbers of boreholes outside the periphery of the tank upto the depth of 50m. Brief description of different soil layers upto the investigated depth along the soil profile is shown in Figure 1. After completion of field tests, subsoil properties have been evaluated and are presented in Table-1.

`

Figure 1. General soil profile of the site

Table 1. Engineering properties of different soil layers

Stra

tum

N v

alue

Bul

k D

ensi

ty

(kN

/m³)

Coh

esio

n

(kN

/m²)

Ang

le o

f int

erna

l fri

ctio

n(°)

mv (

m²/k

N)

Filled up soil consisting of grey silty clay, ash, brick bats etc. –– 18.50 –– –– ––

Very soft to soft brownish grey to grey silty clay / clayey silt (CH/CI) 3 18.10 22 –– 0.000642

Loose to medium dense grey silty sand with mica (SM/SP) 10 18.40 –– 30 ––

Stra

tum

N v

alue

Bul

k D

ensi

ty

(kN

/m³)

Coh

esio

n

(kN

/m²)

Ang

le o

f int

erna

l fri

ctio

n(°)

mv (

m²/k

N)

Very soft to soft grey silty clay with varying percentage of decomposed wood (CH/CI)

4 17.20 18 –– 0.000451

Stiff to very stiff bluish grey to grey silty clay with rusty brown spots and varying percentage of sand (CH)

22 19.25 98 –– ––

Very stiff greyish brown silty clay with varying percentage of sand (CI)

28 19.35 123 –– ––

Dense brownish grey silty sand with mica (SM/SP) 36 21.00 –– 35 ––

2 RESULTS AND DISCUSSIONS

2.1 Soil stratification

It is revealed that in all the boreholes the different stratifications of soil layers are more or less similar. It is also observed that there is a fill layer of about 2m thickness immediately below the ground level. This layer is underlain by a soft clay layer of about 7m thickness followed by a 2m thick sand layer. Below this sand layer there is again a very soft to soft clay layer extending upto a depth of about 28m below the ground level. This layer is underlain by a stiff clay layer of varying thickness and finally followed by a dense sand layer up to great depth. So broadly the two clay layers separated by a thin sand layer are mostly contributing to all the settlement problems.

2.2 Causes of settlement

At this site stone columns of 10m length were installed for overall ground improvement. Stone columns had been supported on the intermediate thin sand layer of limited thickness. Considering three dimensional consolidation of the upper clay layer due to presence of stone columns, an approximate analysis was made to determine the present state of degree of consolidation. It was found that 90% of primary consolidation had already taken place. Still the performance of the stone columns was not satisfactory, rather poor. This may be owing to several reasons. First of all after the tanks were filled for the hydro test, it is not known how the different layers deformed under considerable surcharge load placed on them during tank full condition. Whether or not the already sandwiched sand layer got intermingled within the top and the bottom clay layers is also not certain. In addition to this after placement of this considerable load, the alignment of the stone columns might have got distorted and situations are not unwarranted that the stone columns are just floating in the clay layers with little or no cushion of sand underneath and are unable to perform its designated functions. Besides, instances of noncompliance of the load test results as per the available standards for stone columns were also evident and as such possibility of failure of the same was not beyond much doubt. Secondly stone columns are not like sand drains. Basically they act as soil reinforcements to improve the bearing capacity and reduce settlement. They also provide some amount of radial drainage, but not as effective as sand drains. For stone column installation normally a settlement reduction factor is applied to the total settlement and this finally limits the settlement. Finally the drained water from the lower part of the top clay stratum gets accumulated in the interfacial sand layer and it does not find any outlet to be drained away. As a result the lower part of

0.00

Depth in m

eter

5.00

10.00

BH-01

50.00m

WL=At E.G.L

15.00

20.00

25.00

30.00

35.00

0.00m

40.00

45.00

50.00

BH-02

50.00m

WL=At E.G.L0.00m

BH-03

50.00m

WL= At E.G.L0.00m

9

42

24

11

3

2

2

22

4

6

22

25

2627

31

>100

>100

>100

>100

>100

>100

>100

>100

4

2

23

8

10

4

2

4

34

8

31

16

21

1720

24

>100

>100

>100

>100

>100

>100

>100

>100

3

2

3

7

10

3

2

3

4

59

25

19

22

2426

2557

84

94

>100

>100

>100

>100

>100

>100

2.50m

9.50m

11.50m

28.00m

35.00m

38.80m

CH/CI/MI

SM

CH

CH

CI

SP/SM

1.80m

8.80m

11.50m

28.50m

33.00m

39.00m

CH/CI/MI

SM

CH

CH

SP/SM

CH/CI

1.80m

8.80m

11.50m

27.00m

34.50m

39.00m

CH

SP

CH

CH

CI

SP/SM

Fill Fill

Stratum I

Stratum II

Stratum III

Stratum IV

Stratum V

Stratum VI

Filled up soil consisting of grey silty clay, ash, brick bats etc.:FillVery soft to soft brownish grey to grey silty clay / clayey silt.:Stratum ILoose to medium dense grey silty sand with mica.:Stratum IIVery soft to soft grey silty clay with varying percentage ofdecomposed wood noticed.

:Stratum III

Stiff to very stiff bluish grey to grey silty clay with rustybrown spots and varying percentage of sand.

:Stratum IV

Very stiff greyish brown silty clay with varying percentage of sand.:Stratum VDense brownish grey silty sand with mica.:Stratum VI

2


this clay layer always remains saturated rendering the soil to remain soft perennially. During field boring operations this phenomenon was corroborated by sudden gushing out of water from the boreholes at some point of boring work. This stored water makes the situation all the more complicated. Under such condition, it is very difficult to calculate the actual degree of primary consolidation. Still an effort is made to ascertain the present state of consolidation and portray the future settlement pattern based on available theories and methods. Periodic field observations are also required to ascertain the true scenario at site. In addition to all these reasons another pertinent cause of excessive settlement may be due to closeness of the fire water tanks. The spacing of the three tanks is not adequate and may give rise to concentration of stress at portions where pressure bulbs overlap. 2.2.1 Settlement with time based on the degree of consolidation Table 2.1 shows the average degree of consolidation and corresponding settlement along with its time of occurrence. Table 2.1 Summary of values of time vs. degree of consolidation & time vs. settlement

Uav. (%) Tv

Time, t = 26.09Tv (yr)

Settlement St=Uav x c2=509 x Uav(mm)

5 0.00196 0.051 27.95 10 0.00790 0.206 50.90 20 0.03140 0.819 101.80 30 0.07070 1.845 152.70 40 0.12570 3.279 203.60 50 0.19635 5.123 254.50 60 0.28630 7.469 305.40 70 0.40280 10.509 356.30 75 0.47670 12.437 381.80 80 0.56710 14.796 407.20 85 0.68370 17.838 432.70

Figure 2.1 Time vs. Degree of consolidation curve

Figure 2.2 Time vs. Settlement curve

Based on this table, Figure 2.1 and Figure 2.2 are drawn to depict time vs. degree of consolidation and time vs. settlement behavior respectively. Here all the calculations have been made based on settlement of thicker bottom clay layer as future contributions from the upper clay stratum will be much less in comparison to that of the lower one.

2.2.2 Settlement according to loading condition Table 2.2 and Table 2.3 present the total settlement and time required for 90 percent primary consolidation under various loading conditions. Table 2.2 Summary of values of settlement for various loading conditions of the bottom clay layer

Tank p (kN/m²)

'0p

(kN/m²)

'0p + p

(kN/m²) Total settlement c =mv p (mm)

¼ filled 32.2 148 180.2 197.0

½ filled 50.6 148 198.6 322.0

¾ filled 69.1 148 217.1 419.0

Full 87.1 148 235.6 509.0

Table 2.3 Summary of values of time required for 90% degree of consolidation for various loading conditions of the bottom clay layer

Tank Uav. (%) =

cc

i

ppp 130

Co-eff. Of consolidation cv

(m²/s)

Time reqd.t90 (yrs)=

vcx 275.7848.0

¼ filled 66.0 0.000000116 14

½ filled 40.0 0.000000095 17

¾ filled 31.0 0.000000073 22

Full 26.0 0.000000073 22

In reality all these future projections are supposed to be somewhat lower than these values as already there had been considerable settlement during tank full condition under initial hydro testing. Whenever fire water tanks will be refilled, there will be settlement again. This settlement will continue until primary consolidation of both the clay layers is completed. Besides there will be some immediate settlement of all the layers including the sand layers too. In addition to this secondary consolidation settlement will take place as the clay layers contain some amount of organic matter as well. But settlement contributions due to all these criteria will be much less compared to that of the primary consolidation one. This is why most of the calculations take into consideration of the primary consolidation settlements only. The top clay layer presumably reached a state of faster degree of consolidation due to installation of stone columns. But these stone columns did not serve any purpose of ground improvement for the bottom clay layer. As a result the bottom layer will consolidate under vertical drainage condition only. There will be no radial drainage and consequently it will take more time to complete the primary consolidation settlement. 2.2.3 Comparison with design standard As per IS15284-1(2003) on guidelines for design and construction of stone columns, the acceptable settlement criteria from load test results is 25 to 30mm settlement at the design load for a three column group test. In the present case

0

20

40

60

80

100

0 5 10 15 20 25Time, t (yr)

U av

. (%)

0

100

200

300

400

500

0 5 10 15 20 25Time, t (yr)

Settl

emen

t, St

(mm

)

3


the load test results reveal that most of the settlements have exceeded this limit. As a result satisfactory performance of stone columns has been impaired. According to the same code of practice the granular sand blanket should consist of clean medium to coarse sand compacted in layers to a relative density of 75 to 80 percent. The present condition of the sand blanket at the site does not conform to this criterion even. Its pores have been clogged and mixed with mud slushes.

2.3 Calculation of angular distortion and tilt

Due to inaccessibility, settlement data below the centre of the tank was not available. As a result, field measurement of angular distortion and tilt was not possible. These are calculated approximately from observed settlement at periphery and theoretical one at centre. Here, tilt: δ/R = (δ2-δ1)/R (1)

Where δ = difference of settlement at centre (δ2) and edge (δ1) of tank and R is the radius of the tank. Here δ1 (Observed) =0.727m, δ2 (calculated) =0.776m, and R = 15m. Approximate tilt,

δ/R = (0.776m-0.727m)/15m =0.049/15 = 0.00327 <1/50

For satisfactory performance of the steel tank, tilt should be within 1/30 to1/50 and here it is well within this limit. Angular distortion =Differential settlement between the two extreme ends of the tank ÷ Diameter of the tank =0.141m/30m = 0.0047 > 1/300. Hence it is marginally exceeding this value. 2.4 Remedial measures

Some remedial measures are also suggested to encounter future settlement by means of sand drain or prefabricated vertical drain (PVD), lime column, cement grouting etc.

Sand drain and PVD should have been decided before erection of the tank. But in the present case under consideration the tank has already been erected and as such installation of sand drain or prefabricated vertical drain (PVD) may be done along periphery of the tank and some distance away from it. The length of sand or PVD columns should be extended well up to 15 to 16 m below EGL to strengthen the bottom soft clay layer in addition to the top one. In this method problem may have to be encountered due to presence of already installed stone columns.

Authors have also opined cement grouting below the tank foundation as another alternative method of ground improvement. But as the soil below the tank is predominantly clayey, the permeability is very low. So the effectiveness of cement grout penetrating into the soil voids will be very less. As a result the outcome of this method of ground improvement for control of settlement may not be satisfactory.

2.5 Recommendation

The most viable option remains is by installation of lime column below the tank foundation and along its periphery given the present soil condition. Literature study reveals that cases of ground improvement by using lime column have been done by many researchers in the past (Mittal 2015). In the present study the work by Poorooshasb and Meyerhof (1997) is being suggested for theoretically finding out the effect of installation of lime column and control of settlement. It is proposed that inclined lime column will be used below the tank foundation

using deep mixing technology to increase the shear strength and reduce settlement. In course of the process of installation at first the tanks will be raised from the ground level by using hydraulic jacks. Subsequently installation of the inclined lime columns will be followed from the gaps in between ground level and bottom of the tank and its periphery. Besides, vertical lime columns around the periphery of the tank will have to be installed upto a distance sufficient to intercept any unforeseen failure slip surface. The depth of the lime columns may be suitably decided based on its performance criteria, preferably upto 10m from existing ground level. After the successful installation of lime columns, the sand pad foundations will be freshly prepared and relaid in layers. Literature also reveals that use of geotextile sheet reduces settlement (Kim et al. 1983). Here it is suggested that geotextile sheet will be introduced in layers in the sand pad of suitable thickness for further arresting of the settlement. Subsequently the jacks will be removed and the tank will be placed on the sand pad again.

3 CONCLUSION

It was advised that the tilt and angular distortion at the field are required to be carefully monitored from time to time. Effort should be made to limit these values within permissible limits to avoid any unforeseen situation.

With regard to all remedial measures as described above, it should be noted that all these methods are difficult to be implemented at the site under the present condition as the tanks are already erected. Besides, efficacy of all these methods will not be fullproof as none of the installations can be placed directly underneath the tanks and hence limiting the satisfactory performance of the same.

4 REFERENCES

Babu G.L.S. 2006. An Introduction to soil reinforcement and geosynthetics. Universities press(India) private limited, Hyderabad, India.

Braja M. Das 2010. Advanced Soil Mechanics,third edition, published by Taylor & Francis.

Halkola H.A. 1983. In-situ investigations of deep stabilized soil. Proc. Eighth European Conference on Soil Mechanics and Foundation Engg., Helsinki, Finland, pp.33-36..

IS:15284-1 2003. Design and construction for ground improvement-guidelines,Part 1, stone columns, published by Bureau of Indian Standards,New Delhi.

IS:1904 1986. Code of practice for design and construction of foundations in soils: General requirements,published by Bureau of Indian Standards, New Delhi.

Jansen H.L., Den H. and Netherlands G. 1983. Vertical drains: in-situ and laboratory performance and design considerations. Proc. Eighth European Conference on Soil Mechanics and Foundation Engg., Helsinki, Finland, pp. 633 – 636.

Khabiri M.M., Khishidari A. and Gheibi, E. 2016. Effect of tyre powder penetration on stress and stability of the road embankments. Road Materials and Pavement Design, Taylor & Francis, London.

Kim Y.S., Shen, C.K., and Bang, S. 1983. Oil storage tank foundation on soft clay. Proc. Eighth European Conference on Soil Mechanics and Foundation Engg., Helsinki, Finland, pp. 371-374.

Mittal S. 2015. An Introduction to Ground improvement Engineering. Scientific International Pvt. Ltd., New Delhi, India.

Poorooshasb H.B. and Meyerhof G.G. 1997. Analysis of behavior of stone columns and lime columns. Computers and Geotechnics, Elsevier Science Ltd., Vol.20, No.1,p.p.47-70.

SP36 (Part1) 1987. Compendium of Indian standards on soil engineering: laboratory testing of soils for civil engineering purposes,Part1, Bureau of Indian Standards, New Delhi

SP36 (Part2) 1988. Compendium of Indian Standards on soil engineering: field testing of soils for civil engineering purposes, Part2, Bureau of Indian Standards, New Delhi.

4


Feasibility of ion exchange membranes to control pH changes during electro-osmotic consolidation of soft soils.

Évaluation de la faisabilité des membranes échangeuses d'ions pour contrôler les changements de pH lors de la consolidation électro-osmotique des sols doux Lucas Martin & Jay N. Meegoda, Ph.D., PE, FASCE Dept. of Civil and Environmental Engineering, New Jersey Institute of Technology, United States, [email protected]

ABSTRACT: Electro-osmosis is an established method of consolidating soft fine grained soils. The efficiency of electro-osmotic treatment is controlled by the electrical resistance of the soil-electrode system. Due to increase in soil resistance during treatment, its cost efficiency is reduced limiting the widespread use of this technique especially in developed nations. According to the Helmholtz-Smoluchowski model of electro-osmotic flow the zeta potential is directly proportional to the electro-osmotic permeability. One of the main causes of increased resistance is hydrolysis of water molecules around the electrodes. The acidification of the anode, in particular, reduces the negative surface charge of clay particles and, thus, the zeta potential. This paper studies the use of ion exchange membranes to assess their ability to prevent flow of hydrogen ions into the soil mass. The test with anion exchange membrane showed a more stable pH in the soil around the anode compared to a control test. Contrary to expectations, the cation exchange membrane used around the cathode reduced the hydraulic conductivity of the system such that little water was drained throughout the test, showing that drainage through the electrode will not be sufficient.

RÉSUMÉ : L'électro-osmose est une méthode établie pour consolider les sols fine. L'efficacité du traitement électro-osmotique est contrôlée par la résistance électrique du système sol-électrode. En raison de l'augmentation de la résistance du sol pendant le traitement, sa rentabilité diminue, limitant l'utilisation généralisée de cette technique, en particulier dans les pays développés. Selon le modèle Helmholtz-Smoluchowski d'écoulement électro-osmotique, le potentiel zêta est directement proportionnel à la perméabilité électro-osmotique. L'une des principales causes d'une résistance accrue est l'hydrolyse des molécules d'eau autour des électrodes. L'acidification de l'anode, en particulier, réduit la charge superficielle négative des particules d'argile et donc le potentiel zêta. Cet article étudie l'utilisation de membranes échangeuses d'ions pour évaluer leur capacité à empêcher l'écoulement d'ions hydrogène dans la masse du sol. Le test avec la membrane d'échange d'anions a montré un pH plus stable dans le sol autour de l'anode par rapport à un test de contrôle. Contrairement aux attentes, la membrane d'échange de cations utilisée autour de la cathode a réduit la conductivité hydraulique du système de telle sorte qu'une petite eau a été drainée tout au long de l'essai, montrant que le drainage à travers l'électrode ne suffira pas. KEYWORDS: electro-osmosis; consolidation of soft soils; ion exchange membrane; pH control; soil resistance;

1 INTRODUCTION.

When subjected to loading, clay soils will consolidate and will undergo significant settlement which can have detrimental effects on structures. Due to the low permeability of clay, primary consolidation takes longer time to achieve. The consolidation period can be further expedited by electro-osmosis (Bergado et al., 2000). Electro-osmotic treatment has been extensively tested and it has proven to have clear benefits to consolidation of cohesive soils. However, certain problems have prevented the widespread use of electro-osmotic consolidation especially in developed nations.

One of the most the most widely used theories to model electro-osmotic flow is the Helmholtz-Smoluchowski model. The rate of water flow is controlled by the balance between the friction between the liquid and the capillary wall of soil pores and the electrical force causing water movement (Mitchell and Soga, 2005). In this model, the electro-osmotic permeability of the soil, ke, is calculated by,

ke = ζDn/η (1)

where ζ is the zeta potential, D is the relative permittivity, n is the porosity, and η is the viscosity. According to double layer theory, the slip plane in electrokyneticc processes is located a small distance away from the clay surface. The zeta potential refers to the electric potential caused by the clay particle’s surface charge at the slip plane. According to this model the capacity of electro-osmosis to transport water is directly proportional to the zeta potential of the soil, which is closely related to the resistance of the soil.

1.1 Hydrolysis of water molecules at the electrodes

The application of an electric field induces movement of water across the soil but also generates electrochemical reactions at the electrodes that negatively affect the performance of the electro-osmotic consolidation. The main reaction is the hydrolysis of water molecules (Acar et al. 1990). As water decomposes, hydroxide ions are produced at the cathode and hydrogen ions are produced at the anode, as shown in Eqs. 2 and 3. At the anode (oxidation): 2H2O → O2(g) + 4H+ + 4e-, Eo = 1.229V (2) At the cathode (reduction): 4H2O + 4e- → 2H2(g) + 4OH-, Eo=-0.828V (3) The generation of H+ at the anode causes low pH over time. The pH drops are associated with a reduction of the absolute value of the zeta potential and an increase in soil resistance, decreasing the electro-osmotic flow during direct current application (Rabie et al. 1994, Tuan et al. 2008). Change in the clay properties, both physical and chemical were reported by Mitchell (1991) and Lo et al. (1991) due to pH and zeta potential. Aziz et al. (2006) reported that the pH gradient in the soil sample might change the particle aggregation. For kaolinite, as the pH of the sample decreases from 10 to 3, the absolute value of the zeta potential decreases from 90 to 20 mV, this implies that the physical state of the soil particles changes from dispersed to coagulated (Mahmoud et al. 2010). On the other hand, high concentrations of OH- cause precipitation of

5


metallic ions in the soil, which reduces the porosity. Hu et al, 2015 showed that the impact of change in pH can be mitigated by intermittent current. Hu et al. 2016 also showed that the impact of change in pH can be mitigated by having a metal electrode made of copper.

1.2 Ion-exchange membranes

In order to surpass the adverse effects of hydrolysis and pH change at the electrodes electro-osmosis can be enhanced with the use of electro-dialysis (ED). This process uses an ion exchange membrane (IEM) to prevent the flow of charges ions. Two types of membranes can be used: anion exchange membranes (AEMs) that allow only anions to flow through, and cation exchange membranes (CEMs) that only allow cations to flow through. A sample picture of an ion exchange membrane is shown in Figure 1. The configuration of the electro-osmotic process combined with both membranes is shown in Figure 2.

Figure 1. Sample ion exchange membrane

Figure 2. Schematic of electro-osmotic treatment of soil using ion

exchange membranes This study examines the use of an AEM alone to assess its effect on the electro-osmotic process and quantify them apart from a CEM. Later experiments will test the CEM alone and then both combined to evaluate which arrangement provides the best results. 2 MATERIALS AND METHOD The study consisted of two electro-osmosis tests. Test 1 was used as a control. After preparation, the sample was connected to a power supply and 15 volts of DC were applied. During this time, an overburden pressure was maintained to prevent crack formation. 2800g of weight were applied on a plastic cover that roofed the sample, distributing the load evenly across the top. This was based on the ability of the wet sample to take load without failing. Water was drained through a drainage pipe connected to the cathode reservoir. After 40 hours the samples were disconnected and prepared for pH measurements. During the test, settlement and current were measured at regular intervals. pH measurements were also taken for the drained water. Test 2 introduced an anion exchange membrane at the

anode. For these tests, the anode reservoir was filled with deionized water to allow for hydrolysis to occur. Table 1. Soil Properties.

Soil Composition (by weight) Value

Brown Kaolin (%) 50

Rock flour (%) 50

Liquid Limit (%) 33.5

Plastic Limit (%) 16.9

Soil pH 6.13

Water content (%) 37.5

2.1 Soil sample

Sample soil preparation consists of first mixing brown kaolin clay and rock flour. The mixture is mixed with water to a moisture content of 37.5%. The mixed sample is allowed to rest for 24 hours inside a vacuum oven to remove entrapped air. After this period the sample is placed in the testing chamber and loaded to allow of normal consolidation to occur. Properties of the used samples are shown on Table 1.

2.2 Membrane Preparation

For the anion exchange membrane (AEM), it was prepared for use by soaking it in a 5% NaCl solution for 12 hours. This allowed the membrane to hydrate and expand. After this, the membrane was placed at the anode between the electrode and the soil. Membrane properties are listed in Table 2. Table 2. Anion exchange membrane properties

Functional Group Quaternary

Ionic Form Chloride

Thickness (mm) 0.45±0.025

Electrical Resistance (Ohm.cm2) <40

Total Exchange Capacity (meq/g) 1.3±0.1

Water Permeability (ml/hr/ft2) @5psi <3

2.3 Testing chamber

Figure 3 shows a schematic diagram and dimensions of the rectangular testing chamber. The initial soil cell dimensions were 100mm x 80mm x 40 mm. A small drainage tube in the cathode reservoir allowed for drainage of removed water.

Figure 3. Schematic of testing cell.

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3 RESULTS AND DISCUSSION

3.1 pH

The variations of pH in the soil bed are shown in Figure 4. As the hydrolysis proceeds, hydroxide ions are produced at the cathode, whereas at the anode protons are produced, this results in a pH gradient across the soil (Yoshida 2000, Yuan and Weng 2003). The acid front near the anode and base front near the cathode migrate towards each other. The acid front moves faster than the base front due to the higher mobility of H+ than OH-, and therefore low pH dominates the chemistry across the soil except for a small region close to the cathode (Alshawabkeh & Bricka, 2000). The control tests reflects this phenomena. The pH around the anode drops to 3.9 and rises to 9.5 at the cathode, indicating that hydrolysis has occurred affecting the soil pH as expected. The pH at the center of the sample is acidic compared to the original, showing that the acidic front dominates. Test 2 combines electro-osmosis with an anion exchange membrane to prevent the flow of hydrogen ions into the soil near the anode and reduce the change in pH. The pH of Test 2 near the anode decreased to 5.0, even with in the presence of the membrane. This might be due to the exchange capacity of the membrane. As hydrolysis takes place, the membrane prevents the passage of H+ ions into the soil. However, eventually the membrane is depleted and ions can pass more freely. The membrane used had a low hydraulic permeability, thus passage of ions from the anode reservoir would still be partially thwarted even after depletion. The pH at the cathode is actually higher than that of the control. Since the membrane prevented the flow of hydrogen ions into the soil bed, the zeta potential of clay particles was better maintained. This is evidenced by the lower resistance of Test 2 as shown in Figure 5. Consequently, the current throughout the test is higher (Figure 6) and hydrolysis occurs at a greater rate. This slightly greater generation of hydroxide ions increases the pH at the cathode to 10.1. At the center of the soil bed the pH for Test 2 is higher than the control, even higher than the initial pH. Since the hydrogen ions are trapped in the anode reservoir, the basic front generated at the cathode can migrate towards the anode and increases the pH of the soil. This further shows that the membrane prevented over acidification of the soil.

Figure 4. pH across soil bed after 40 hours of electro-osmotic treatment. (a) Test 1: control; (b) Test 2: electro-osmosis with anion exchange membrane The pH of the drained water and the water in the anode reservoir were also measured. These values are shown in Table 3. The drained water pH corresponded with the pH of the soil near the electrodes. Both had high pH, with Test 2 showing the higher value. For Test 2, the anode reservoir was filled with deionized water up to a height equal to the soil to avoid creating a hydraulic gradient. The deionized water served as the source of water molecules for hydrolysis to take place. Because the membrane prevented the generated hydrogen ions from flowing

into the soil, the pH of the water in the anode reservoir decreased intensely. The pH was found to be below 1. This indicated that the membrane succeeded in keeping the hydrogen ions from entering the soil bed. A yellowish coloration and faint smell also formed in the water. Because the membrane has an exchange capacity limit, once it depletes, hydrogen ions may pass through it into the soil. If the membrane was depleted during the test and hydrogen ions were allowed to migrate, this could explain the low pH of the soil at the anode in Test 2. While it is not as low as that of Test 1, the soil still shows more acidity than the initial value. In the future, drainage and replacement of the water in the anode reservoir could be beneficial to avoid acidification of the soil once the membrane depletes. Table 3. pH measurements for drained water

Test 1: Control

Drained water pH 10.17

Test 2: EO + AEM

Drained water pH 10.79

Anode reservoir pH 0.5*

*The pH meter user had a minimum safe range of 1. Thus, the measurement obtained for the anode reservoir is below 1 but unreliable beyond that.

3.2 Electrical resistance and current

In accordance with the literature, the resistance of the soil increased as electro-osmosis was carried out. The resistance of the soil throughout testing was measured in one minute intervals for 40 hours. The results are shown in Figure 5. Both tests display an increasing resistance. However, Test 1 experiences a resistance 4.8 times greater than that of Test 2. The membrane does increase the resistance in Test 2 by a fixed amount; however the trends still show its positive effects.

Figure 5. Soil resistance during 40 hours of electro-osmotic treatment. (a) Test 1: control; (b) Test 2: electro-osmosis with anion exchange membrane Figure 6 shows the variation in current through the soil over time. According to Ohm’s law, the current is directly related to the resistance, thus as resistance increases the current decreases. While the current is still high compared to the initial value, and although the rate at which it decreases is low, the current can be expected to reach very low values, and even zero, if electro-osmosis is continued. This study ended after 40 hours to study the immediate effects of a membrane. If the test was continued until current reached zero the membrane would have long been depleted and its effects likely nullified by the highly acidic water in the anode reservoir. Both Figures 5 and 6 show some jumps, especially at around 1000 minutes. These are probably due to a change in lab conditions, which have been known to affect precise measurements.

7


Figure 6. Current through the soil during 40 hours of electro-osmotic treatment. (a) Test 1: control; (b) Test 2: electro-osmosis with anion exchange membrane

3.3 Settlement

A settlement gauge was placed on the center of the soil bed to measure the settlement of the sample as electro-osmosis was applied. Figure 7 shows the settlement as a function of time. The application of a direct current induced settlement on both samples. Test 2 showed increased settlement due to the use of the anion exchange membrane. Both tests show an initial high settling rate that plateaus after about 18 hours. Following this, settlement continues but at a much lower rate. Because the membrane prevented the flow of hydrogen ions into the soil bed, the absolute value of the zeta potential was not as affected and the resistance in Test 2 did not increase as rapidly as Test 1. This allowed for a higher current and, thus, higher electro-osmotic flow, leading to increased consolidation.

Figure 7. Settlement at the center of soil bed during 40 hours of electro-osmotic treatment. (a) Test 1: control; (b) Test 2: electro-osmosis with anion exchange membrane

4 CONCLUSIONS

The efficiency of electro-osmotic consolidation is significantly affected by the changes in pH in the soil, especially around the electrodes. In an effort to optimize the method to allow its commercial use, many studies have been done. This study asses the possibility of use of anion exchange membranes at the anode to isolate hydrolysis of water around the anode and prevent the flow of hydrogen ions into the soil. Two tests were performed to analyze the effects of the membrane. During these tests, the resistance, current, and settlement of the soil samples were measured. After the tests, the pH through the soil and in the drained water was also measured. The membrane showed very positive results in all respects when compared to conventional electro-osmotic treatment. The pH of the soil around the anode did not decrease as much as with in the control test. It still decrease compared to the initial value. This is likely due to depletion of the exchange capacity of the membrane. The resistance of the soil was shown to

increase at a slower rate for the test with the membrane. This further affirms that the membrane produced a positive effect. The increased settlement of Test 2 was also very positive. The use of a membrane allowed for consolidation beyond that obtainable with simple electro-osmosis. The use of membranes should be investigated further with respect to electro-osmotic consolidation. The use of an cation exchange membrane should be investigate as well as its coupled effect with the anion exchange membrane. Especial attention should be given to drainage of water during treatment. Depending on the hydraulic permeability of the cation exchange membrane used, drainage through the electrode, as was the case in this study, might not be possible. Additionally, the capacity of a membrane to prevent the flow of ions before it becomes depleted should be taken into account and investigated. While membranes might provide a significant improvement to the electrical properties of the soil, if its effects are too short it might not be sufficient to help popularize electro-osmotic consolidation. Despite using the membrane, the resistance of the soil still increased. This demonstrates the acidification of the soil around the anode is not the only force reducing electric efficiency.

5 REFERENCES

Acar Y.B., Gale R.J., Putnam G.A., Hamed J., and Wong R.L. 1990 Electrochemical processing of soils: theory of pH gradient development by diffusion, migration, and linear convection. Journal of Environmental Science and Health Part A Environmental Science Engineering 25(6), 687-714

Alshawabkeh A.N. and Bricka M. 2000. Basics and applications of electrokinetic remediation. In: Wise, D.L., Trantolo, D.J., Cichon, E.J., Inyang, H.I., Stottmeister, U. (Eds.), Remediation Engineering of Contaminated Soils. Marcel Dekker, Inc., New York, NY, pp. 95-111.

Aziz A.A.A., Doxin D.R., Usher S.P., and Scales P.J. 2006. Electrically enhanced dewatering (EED) of particulate suspensions. Colloids and Surfaces A 290, 194-205.

Bergado D. T., Balasubramaniam A. S., Patawaran M. A. B., and Kwunpreuk W. 2000. Electroosmotic consolidation of soft Bangkok clay with prefabricated vertical drains. Ground Improvement 4, 153-63.

Hu, L., Wu, H., and Meegoda, N. J. 2016. Effect of electrode material on electro-osmotic consolidation of bentonite, The 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering. Japanese Geotechnical Society Special Publication.

Hu, L., Wu, H., Meegoda, N. J., Wen, Q. 2015. Experimental and Numerical Study of Electro-Osmosis on Kaolinite under Intermittent Current. Geotechnical Engineering Journal of the SEAGS & AGSSEA 46 (4).

Lo K.Y., Ho K.S., and Inculet I.I. 1991. Field test of electro-osmotic strengthening of soft sensitive clay. Canadian Geotechnical Journal 28, 74-83.

Mahmoud A., Olivier J., Vaxelaire J., and Hoadley A.F.A. 2010. Electrical field: A historical review of its application and contributions in wastewater sludge dewatering. Water Research 44, 2381-2407.

Mitchell, J.K. 1991. Conduction Phenomena: from theory to geotechnical practice. Geotechnique, 41 (3), 299-340.

Mitchell J. K. and Soga K. 2005. Fundamentals of Soil Behavior. 3rd ed. Hoboken, New Jersey.

Rabie H.R., Mujumdar A.S., Weber M.E. 1994. Interrupted electroosmotic dewatering of clay suspensions. Separations Technology 4(1), 38-46.

Tuan P.A., Jurate V., Mika S. 2008. Electro-dewatering of sludge under pressure and non-pressure conditions. Environmental Technology 29, 1075-1084.

Yoshida H. 2000. Electro-osmotic dewatering under intermittent power application by rectification of a.c. electric field. Journal of Chemical Engineering of Japan 33(1), 134-140.

Yuan C. and Weng C.H. 2003. Sludge dewatering by electrokinetic technique: Effect of processing time and potential gradient. Advances in Environmental Research 7(3), 727-732.

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Table 1. Composition of soils used.

Component (%)

samples Clay Silt Sand

Ariake clay 23.8 57.8 18.4 Red soil 9.2 50.6 40.1

Andosol 12.6 57.9 29.5 Decomposed

19.8 54.4 25.9 granite soil

Consolidation Properties of Soft Clay Mixed with Useful Microorganisms and Application of Simple Dehydration Method

Propriétés de consolidation de l'argile douce mélangée à des microorganismes utiles et à l'application d'une méthode de déshydratation simple

Kiyoshi Omine & Satoshi Sugimoto Graduate School of Engineering, Nagasaki University, Japan, [email protected]

ABSTRACT: Influence of microorganisms on consistency property of various types of soils was investigated. It is found that the microorganisms such as lactic acid or photosynthetic bacteria influence the liquid limit and plastic limit of soils. It is also clarified that the microorganisms influence the consolidation property of clay with high content of organic matters. Dehydration of soft soils is one of methods for treating sludge, because soft clay with high water content cannot be used as geo-material. In this study, a simple dehydration method with siphon system is proposed. It is confirmed that the dehydration method is enable to decrease water content of very soft clay to near liquid limit. From the consolidation and dehydration tests of sludge in pond, it is found that mixing photosynthetic bacteria increases permeability of the soft clay and accelerates consolidation.

RÉSUMÉ : L'influence des microorganismes sur la propriété de cohérence de divers types de sol a été étudiée. On constate que les microorganismes tels que l'acide lactique ou les bactéries photosynthétiques influencent la limite de liquide et la limite plastique des sols. Il est également précisé que les microorganismes influent sur la propriété de consolidation de l'argile avec une teneur élevée en matières organiques. La déshydratation des sols doux est l'une des méthodes de traitement des boues, car l'argile molle à haute teneur en eau ne peut pas être utilisée comme matériau géométrique. Dans cette étude, une simple méthode de déshydratation avec système siphon est proposée. Il est confirmé que la méthode de déshydratation permet de diminuer la teneur en eau de l'argile très douce à une limite proche du liquide. À partir des essais de consolidation et de déshydratation des boues dans l'étang, on constate que le mélange de bactéries photosynthétiques augmente la perméabilité de l'argile molle et accélère la consolidation. KEYWORDS: Soft clay, Microorganism, Consolidation, Dehydration

1 INTRODUCTION

Many microorganisms exist in natural soils. However, the influence of microorganisms on engineering properties of soils has not been clarified sufficiently in geotechnical engineering field.

Generally, microorganisms have an important role in agricultural soils Purple non-sulfur bacteria are one type of photosynthetic bacteria, which can live and grow in light. They are widely distributed in anaerobic environments like paddy field, river, lake, pond, seawater and wastewater plants. It was found that these bacteria are effective for stimulating plant growth (Kondo et al., 2004). Lactic acid bacteria exist widely in nature. It was confirmed that lactic acid bacteria accelerate the decomposition of organic amendments in soils and increase the release of nutrients that are necessary for plant growth (Higa et al., 1989).

It is not easy to use soft clay with high water content as geo-material. Recycling of sludge is one of important issues to be solved in geo-environmental problems. There are many treatment methods of soft clay, for example, mixing with sandy soil or solidification using cement-based agent. Dehydration of soft soils is also one of method for recycling of sludge. It is important to consider reducing environmental impact.

In order to investigate influence of microorganisms on consistency property of various types of soils, lactic acid and photosynthetic bacteria are used (Omine et al., 2015). Influence of the microorganisms on the consolidation property of clay with high content of organic matters is also investigated. In this study, a simple dehydration method with siphon system is proposed. It is confirmed that the dehydration method is enable to decrease water content of very soft clay to near liquid limit. Consolidation and dehydration tests of sludge in pond are performed. The influence of photosynthetic bacteria on permeability and compressibility of the soft clay is clarified.

2 INFLUENCE OF MICROORGANISMS ON CONSISTENCY OF SOILS

2 .1 Soil samples

In order to investigate the influence of microorganisms on chemical and physical properties of soils, a laboratory experiment was conducted with three different types of soils, namely Ariake clay, red soil and andosol.. Ariake clay is a typical marine clay in Japan. Red soil (Kunigami mahji) was sampled at Okinawa in Japan. Andosol (Kuroboku soil) is a volcanic ash clayey soil , collected from Kumamoto in Japan. The grain size distributions of these soils were measured by the laser diffraction particle size analyzer and the results are shown in Table 1.

2 .2 Microorganisms

Purple non-sulfur photosynthetic bacteria were used in this study. The bacteria are on the market and cultured from paddy field soils. It is possible to culture the bacteria in a

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208.7

213.0

223.7

219.0

225.0

200

205

210

215

220

225

230

Water

Lactic

acid b

actrei

a×10

0

Photos

ynthe

tic ba

cteria

×100

Lactic

acid b

actrei

a×10

Photos

ynthe

tic ba

cteria

×10

Liqu

id li

mit

(%)

(a) Ariake clay (b) Red soil (Kunigami-mahji) (c) Andosol (volcanic ash soil)

Figure 1. Changes of Liquid Limit and Plastic Limit on each soil (×10 or 100: a dilution ratio of 10 or 100 times).

Table 2. Values of pH of soil samples with or without the bacteria.

Water Lactic acid bacteria×100

Photosynthetic bacteria×100

Lactic acid bacteria×10


Ariake clay 6.75 6.76 6.86 6.88 7.10 Red soil 5.84 5.87 5.87 6.00 5.89 Andosol 5.81 5.86 5.86 5.86 5.84

(×10 or 100: a dilution ratio of 10 or 100 times)

Table 3. Electric conductivity of soil samples with or without bacteria.

Water Lactic acid bactreia×100


Lactic acid bactreia×10


Ariake clay 3.32 3.55 3.30 3.45 3.41 Red soil 0.174 0.191 0.194 0.197 0.198 Andosol 0.149 0.189 0.194 0.224 0.233

(unit: mS/cm, ×10 or 100: a dilution ratio of 10 or 100 times)

nutrient medium containing ammonium, sodium, potassium, yeast extract etc. under sunlight and incubating under anaerobic condition for a week.

Lactic acid bacteria are also used. It is easy to culture these bacteria by mixing water, rice bran (or unpolished rice), granulated sugar and salt under anaerobic condition for a week.

2 .3 Laboratory test

A known volume of the lactic acid bacteria or photosynthetic bacteria was mixed with each soil types. The culture solutions of these bacteria were diluted with distilled water and made 10 or 100 times dilutions In consideration of a natural water condition of soils, the diluted culture solutions were mixed with 11, 12 and 20g of clay, red and ash clay soils, respectively. The bacteria inoculated soil samples were cured under constant

22


temperature of 25ºC and humidity of 90% for a week. Regarding the chemical properties of soils, pH and electric

conductivity (EC) on the soil samples mixed with distilled water of 5 times were measured in a dry condition.

Liquid limit and plastic limit tests were also performed on each soil sample for evaluating the consistency property.

2 .4 Test results

Values of pH on soil samples with or without the bacteria are shown in Table 2. pH of undiluted solutions of the lactic acid bacteria and photosynthetic bacteria were 3.16 and 8.28, respectively. Though the pH of the lactic acid bacteria was low, the pH of each sample was slightly increased in comparison with the control.

Values of EC on soil samples with or without the bacteria are shown in Table 3. After mixing the bacteria, the EC of the samples was increased due to the presence of nutrients in the the culture solution.

Changes in Liquid Limit (LL) and Plastic Limit (PL) on each soil sample with or without the bacteria are shown in Fig.1. It is confirmed that the LL and PL of all soil samples increased by adding the bacteria. This trend became clear when the dilution ratio was small, except for PL in andosol soils. It was found that the consistency of the soils depends on the bacteria.

3 CONSOLIDATION PROPERTY OF SOFT CLAY MIXED WITH PHOTOSYNTHETIC BACTERIA AND APPLICATION OF DEHYDRATION METHOD

3 .1 Soil samples and mechanical property

Pond sludge at Nagasaki prefecture is used as a sample of soft clay. Natural water content of the sludge was 144.8 %. Clay content is 47% and density of soil particles is ρs 2.73g/cm3. The sludge mixed with photosynthetic bacteria of 1 % in a mass is also prepared and cured for a week at constant temperature of 30˚C. Consistency and ignition loss of the clays are shown in Table 4. Liquid and plastic limits of the clay with the bacteria increase and plastic index of the clay with the bacteria decreases.

Table 4. Mechanical property of the sludge with or without the bacteria.

Sample Liquid limit wL (%)

Plastic limit wP (%)

Plastic index IP

Ignition loss (%)

Clay 122.1 40.6 81.5 14.9 Clay with

photosynthetic bacteria

123.0 42.3 80.7 15.0

3 .2 Consolidation property

Consolidation test was performed on specimens of the clays in a size of 60 mm in diameter and 20 mm in height. The clays in a slurry was poured into a consolidation mold.

Relationship between coefficient of permeability and consolidation pressure of the clay with or without the bacteria is shown in Fig.2. It is found that the coefficient of permeability on the clay with the bacteria increases comparing with that of the clay without the bacteria at the same consolidation pressure. Influence of the bacteria on the coefficient of consolidaiton is shown in Fig.3. The value of coefficient of consolidation also increases after mixing the bacteria.

It is considered that the photosynthetic bacteria promote a degradation of organic matters or have any activation effect. It is expected that the lactic acid bacteria also have similar effect. Similar effect of increasing permeability after adding the photosynthetic bacteria has been observed on the in-situ ground of the decomposed granite soil with low permeability (Omine et al., 2015).

Figure 2. Relationship between coefficient of permeability and consolidation pressure of the clay with or without the bacteria.

Figure 3. Relationship between coefficient of consolidaiton and consolidation pressure of the clay with or without the bacteria.

3 .3 Dehydration method with siphon

Simple dehydration method with siphon is used. A schematic diagram of the apparatus is shown in Fig.4. A container in width of 24 cm, length of 31 cm and height of 10 cm is prepared and nipple pipe is attached on the side. House with 15 mm of inside diameter is equipped with 4 pieces of acrylic string inside. Hose with 3 mm of inside diameter is connected for increasing water head. The acrylic string is used for absorption of water and stimulation of water movement to the hose with 3 mm of inside diameter. After supplying a water to the hose, siphon is applied to the clay and dehydration starts. Four sheets of cloth was placed on the bottom of the container as drainage layer and the clay in a slurry was poured

Nipple pipe

Hose with 15 mm of inside diameter installing acrylic strings

Water head

Hose with 3 mm of inside diameter

Clay

Cloth as drainage layer

Water tank

Figure 4. A schematic diagram of dehydration method with siphon.

23


into the container up to 4 cm in height. The surface of the clay is wrapped in plastic film.

Four samples with different initial water content from 150 to 500 % are prepared. Relationship between amount of total drainage water and elapsed time on the clays with different water content is shown in Fig.5. It is indicated that amount of drainage water of the clay with higher water content increases. For all conditions of the clays, the amount of drainage water becomes almost constant after 10 hours of elapsed time. Initial and final water contents of the dehydration on the clays are shown in Table 5. The liquid limit of the clay is 122.1 %. From the result, it is found that the clay with twice water content of liquid limit can decrease to water content less than liquid limit after dehydration.

In order to confirm the effect of water head on the siphon, dehydration test was performed under different length of the hose. Relationship between negative pressure and elapsed time under the water head of 2 or 8 m is shown in Fig.6. Negative pressure was measured by installing water pressure meter to the nipple pipe. The maximum negative pressure of 8 kPa was obtained in the condition of 2 m of water head. On the other hand, the maximum value was 25 kPa at the condition of 8 m of water head and several peaks was shown. The amount of total drainage water increased by 20%.

0

500

1000

1500

2000

2500

3000

3500

0 5 10 15 20 25

Am

ount

of t

otal

dra

inag

e w

ater

(g)

Elapsed time (h)

Water content w0=500%

w0=450%

w0=300%

w0=150%

Figure 5. Relationship between amount of total drainage water and elapsed time on the clays with different water content (water head: 2 m).

Table 5. Water contents of the clays before and after dehydration (water head: 2 m).

Initial water content (%) 150 300 450 500 Water content after

dehydration (%) 113.7 115.8 128.6 133.2

-30

-25

-20

-15

-10

-5

0

5 0 500 1000 1500 2000 2500

Neg

ativ

e pr

essu

re P

(kP

a)

Elapsed time (s)

2m

8m

W0=300%

Water head

Figure 6. Relationship between negative pressure and elapsed time under the different condition of water head.

Influence of photsyntheic bacteria on dehydration of the clay is investigated. Figure 7 shows relationship between amount of total drainage water and elapsed time on the clays with or without the bacteria. The amount of drainage of the clay with the bacteria water increases at the same elapsed time. It is found that the coefficient of consolidation calculated from this curve increases at the condition of the clay with the bacteria. This is the same trend in the consolidation test. It is considered that the photosynthetic bacteria have any effect for promoting a degradation of organic matters and the consolidation. The dehydration method using siphon and mixing the bactria is eco-friendly way with reducing environmental impact.

0

500

1000

1500

2000

0 5 10 15 20 25 A

mou

nt o

f tot

al d

rain

age

wat

er (g

)

Elapsed time (h)

Clay with photosynthetic bacteria

Clay

Figure 7. Relationship between amount of total drainage water and elapsed time on the clays with or without the bacteria.

4 CONCLUSION

The following conclusions are obtained from this study. 1) Liquid limit and Plastic limit of soil samples increases

after mixing the microorganism such as lactic acid bacteria or photosynthetic bacterial.

2) Coefficients of permeability and consolidation on the clay with high water content and high organic content increase by mixing the photosynthetic bacterial.

3) Simple dehydration method using siphon is proposed. The dehydration effect is much higher for the clay with high water content. The siphon effect can be increased by increase of water head.

4) It is considered that the dehydration method using siphon and mixing the bactria is eco-friendly way with reducing environmental impact.

5 ACKNOWLEDGEMENTS

The authors wish to acknowledge the financial support by Grant-in-Aid for Scientific Research (15H04039) from Japan Society for the Promotion of Science

6 REFERENCES

Kondo K. Nakata N. Nishihara E. 2004. Effect of Purple Nonsulfur Bacteria (Rhodobacter sphaeroides) on the Growth and Quality of Komatsuna under Different Light Qualities, Environment Control in Biology, Vol.42, No.3, pp.247-253 (in Japanese).

Higa T. and Kinjo S. 1989. Effect of Lactic Acid Fermentation Bacteria on Plant Growth and Soil Humus Formation. First International Conference, Kyusei Nature Farming, pp.140-147.

Omine K. Sugimoto S. and Tutsumi D. 2015 Influence of microorganisms on geo-environmental engineering properties of soils, Proc. of 14th Global Joint Seminar on Geo-Environmental Engineering, 2015, CD-ROM.

24

2.Poster session

Efficiency of improvement methods in compressible soil based on the results of geotechnical monitoring

Efficacité des méthodes d'amélioration dans le sol hautement compressible sur la base des résultats de la surveillance géotechnique

Jana Frankovská & Miloslav Kopecký Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Slovak Republic, [email protected] Peter Mušec & Viktor Janták Orgware, Bratislava, Slovak Republic

ABSTRACT: The presented paper is focused on soil improvement of highly compressible soils. The paper summarizes soil improvement methods used during the road and embankments construction in Slovakia. In the areas of Neogene sediments in Slovakia, adverse strength-deformation properties of clay layers in combination with groundwater pressure in sandy layers present a relatively high risk for the preparation and construction of cuts and embankments, as documented by examples in this paper. In order to illustrate clay improvements, the most frequently used methods in Slovakia and case studies on ground improvement are presented. Efficiency of improvement methods based on the results of geotechnical monitoring is analysed in comparable engineering-geological and hydrogeological conditions.

RÉSUMÉ: Le présent article se concentre sur l'amélioration des sols hautement compressibles. Le document résume les méthodes d'amélioration des sols utilisées lors de la construction de routes et de remblais en Slovaquie. Dans les zones de sédiments néogènes en Slovaquie, les propriétés de force-déformation des couches d'argile défavorables en combinaison avec la pression des eaux souterraines dans les couches sablonneuses présentent un risque relativement élevé pour la préparation et la construction de tranchées et de remblais, comme le montrent les exemples présentés dans ce document. Afin d'illustrer les améliorations apportées à l'argile, trois des méthodes les plus souvent utilisées en Slovaquie et quelques études de cas sur l'amélioration du sol sont présentées. L'efficacité des méthodes d'amélioration basées sur les résultats de la surveillance géotechnique est analysée pour comparable conditions d'ingénierie géologique et d'hydrogéologie. KEYWORDS: soil improvement, stone columns, vertical drains, stone drainage ribs, geotechnical monitoring.

1 INTRODUCTION

In many regions of Slovakia motorway embankments have to be built on soft silts or clays or on the surface with deposits which may contain layers of peat or organic material. The engineer may choose between two alternatives: to remove the soft soil or to improve the soil to support the embankments with acceptable settlement. Since compressible soils have usually low permeability, the time needed for the desired consolidation can be very long. Soil improvement methods used during the road embankments construction in Slovakia are introduced at two different construction sites with comparable ground conditions.

Road embankments represent a special geotechnical challenge if they comprise embankments on very soft ground (Correia et al, 2014). Various techniques for ground improvement are in use many decades to reduce the settlement of embankments and to accelerate the consolidation settlement of soft clay layers such as preloading, soil replacement, lime/cement stabilization, dynamic consolidation, vibro-stabilization, vertical drains, deep mixing methods or reinforced soil (Vaníček I. and Vaníček M. 2008). Moreover, other more innovative solutions recently developed are also available, including brick–fibre-concrete (Vaníček I. and Vaníček M. 2013), natural and synthetic fibres (Nguyen et al, 2015) or tyre powder penetration and tyre bales (Saberian M. et al, 2017, Khabiri et al, 2016, Winter, 2014). In most European countries current earth- or rock fill embankments are studied and built following well established procedures (Correia et al, 2014).

2 SOIL IMPROVEMENT METHODS USED DURING ROADS CONSTRUCTION IN SLOVAKIA

The selection of improvement techniques for a particular project depends on geological conditions, soil characteristics, rate of consolidation, and height of embankment, cost, and timelines. Other factors with impact on ground improvement method in the areas of soft and compressible soil layers are the area, depth of improvement, time available for soil treatment, and acceptable settlements. Vertical drains, stone columns, dynamic compaction, preloading, and stone drainage ribs are commonly used in geotechnical practice in Slovakia.

Vertical drains are used to achieve accelerated radial drainage and consolidation by reducing the length of the drainage paths. Stone columns are a specific type of vibro compaction techniques, in which stone aggregates are added by means of special depth vibrators (Priebe, 1995). They reduce settlements because they act as rigid inclusions within the compressible soil. The correct choice of stone column construction method and proper on-site implementation are the keys to successful improvement of soft and very soft soil. Vibro replacement stone columns are a relatively quick and effective technology for soil improvement and reinforcement. Vertical drains are generally very effective except where they are installed in organic soils, in highly stratified soils, or where serious stability problem exist (Moseley and Kirsch 2004). At the top of stone columns gravel layer is installed. Stone columns are often combined with preloading to increase efficiency of improvement system.

Prefabricated vertical drains are made of a plastic core surrounded by a geotextile that acts as a filter to prevent

31

clogging. The advantage of using this method is reduction of construction time.

Stone-filled ribs (drainage trenches) are often used as ground improvement method in soft clays in Slovakia. 3 RESULTS BASED ON GEOTECHNICAL MONITORING FOR EMBANKTMENTS

The case study is located in central Slovakia near the city Banovce nad Bebravou, the section of the motorway R2 Ruskovce – Pravotice with the length 10,8 km (Fig. 1).

The geological conditions of the tested area consist of very soft layers of Quaternary and Neogene sediments under the Paleogene sediments, mostly claystones. The line of the motorway R2 Ruskovce - Pravotice is located in the area of Neogene marine and lacustrine sediments with a varied grain size distribution. Neogene sediments are overlaid by Quaternary sediments, which consist mostly of eluvial, proluvial and fluvial sediments. The thickness of the cover of Quaternary sediments varies from tens of centimeters to several meters.

Figure 1. Locality - R2 Ruskovce – Pravotice Case studies using 3 different types of soil improvement methods in comparable ground conditions are introduced. Calculated and measured values of the settlement under embankments are compared. Calculations were done for three improvement methods. Settlement and end of primary consolidation was calculated for stone columns, stone drainage ribs (Fig. 2) and also alternatively for vertical drains.

Figure 2. Execution of stone drainage ribs

Geotechnical parameters, including pore pressures and horizontal displacement, are monitored in real time throughout the consolidation period. Ten horizontal inclinometers were installed on the selected sections of road R2 Ruskovce –

Pravotice construction (Fig. 3) with soil improvement using stone columns and stone drainage ribs.

Figure 3. Execution of horizontal inclinometers

3.1 Stone columns

Three profiles of motorway R2 Ruskovce-Pravotice were selected for comparison of efficiency of stone columns installation when improving highly compressible soil under embankments. Geotechnical monitoring using horizontal inclinometers was carried out in these profiles.

The height of embankments in km 1,475 R2 is about 8, 7 m. There are clays with medium plasticity and firm consistency above the high plasticity Neogene clays in the subsoil. Design values of geotechnical parameters are presented in Table 1. Ground water level was measured in the depth of 0, 7 m below the surface. Design and measured values of settlement and dissipation of pore water pressures in km 1,52 of R2 are presented in Table 2.

Design values of settlement for vertical drains and stone columns in km 3,964 and measured values are presented in Table 3.

Design values of settlement for vertical drains and stone columns in the km 10, 183 of R2 motorway and measured values are presented in Table 4.

To illustrate the capabilities of stone columns, field observations of ground settlement in km 3,964 of R2 motorway are shown in Fig. 4.

Table 1. Design values of geotechnical parameters

γ (kN/m3) φ (o) c (kPa) E def (MPa)

Clays CI 19,3 15 16 2,7

Table 2. Design values of settlements for measured values of settlements (MS), vertical prefabricated drains (VD) and stone columns

(SC) in the km 1, 5 of R2 motorway

Method MS VD SC

Settlement (mm) 74,1 296 202 Time for 95 % dissipation of pore pressure (days)

70 120 95

Table 3. Design values of settlements for measured values of settlements (MS), vertical prefabricated drains (VD) and stone columns

(SC) in the km 3, 98 of R2 motorway

Method MS VD SC

Settlement (mm) 55,8 229 170

32

Figure 4. Relationship between loading (construction of embankment) and settlement in km 3,965 of R2 motorway

Table 4. Design values of settlements for measured values of

settlements (MS), vertical prefabricated drains (VD) and stone columns (SC) in the km 10, 183 of R2 motorway

Method MS VD SC

Settlement (mm) 74,1 445 368 Time for 95 % dissipation of pore pressure (days)

- 160 130

The stone columns were designed to be 5 m deep and the distance between the columns was 2 m. Geotechnical structure consists of geotextile, 30 cm of gravel, geogrid, and 20 cm of gravel used at the top of the stone columns. Estimated time scale for 95 % dissipation of pore water pressure was calculated to be 80 to 130 days.

3 .2 Stone-filled ribs (drainage trenches)

Case study were selected in km 1,975 of R2 motorway. The height of embankments is about 10, 5 m. Ground conditions

consist of clays with medium and high plasticity with firm consistency. Neogene clays in the subsoil in the depth about 6 m are medium or high plastic. Ground water level was measured in the depth of 2, 7 m below the surface. Design values of the settlement for vertical drains and stone filled ribs in km 3,964 and measured values are presented in Table 5.

To illustrate the capabilities of stone filled ribs, field observations of ground settlement in km 2,08 of R2 motorway are shown in Fig. 5.

Table 5. Design values of settlements for measured values of settlements (MS), vertical prefabricated drains (VD) and stone filled

ribs (SFR) in the km 1, 975 of R2 motorway

Method MS VD SRF

Settlement (mm) 84,8 277 183

Figure 5. Relationship between loading (construction of embankment) and settlement in km 2,08 of R2 motorway

33

Vertical drains - vibro replacement stone columns were used in profiles in the km 1,475, km 3,98 and km 10, 183 of R2 motorway. Stone filled ribs were used to improve subsoil under embankment in the km 1,975 of R2 motorway.

Design values of settlements for vertical drains and stone filled ribs and measured values during the geotechnical monitoring are summarized in Fig. 6.

Figure 6. Design values of settlements and measured values during the

geotechnical monitoring for vertical drains (1,475 km, 3,98 km and 10,183 km) and stone filled ribs (km 1,975)

4 CONCLUSION

Transportation geotechnics associated with constructing and maintaining properly functioning transportation infrastructure is a very resource intensive activity. Today, there are several ground improvement methods encompassing shallow, medium and deep soil treatments and involving drainage, reinforcement and soil improvement techniques available for geotechnical engineers to choose from, contingent to construction project needs (Correia et al., 2016). Soil improvement methods are used during the road construction in highly compressible soils in Slovakia. Clay layers in combination with high plasticity and groundwater pressure present a relatively high risk for the preparation and construction of cuts and embankments. In order to illustrate clay improvements, three of the most frequently used ground improvement methods in Slovakia were analyzed in comparable engineering-geological conditions based on the results of geotechnical monitoring.

The measured values of embankment settlements during geotechnical monitoring confirmed high efficiency of vertical drains - vibro replacement stone columns used in profiles in the km 1, 475, km 3, 98 and km 10, 183 of R2 Ruskovce-Pravotice motorway. The maximum measured values of settlement were 32 %, 33 % and 37 % of maximum design values (Fig. 6). The maximum measured values of settlement using stone filled ribs to improve subsoil under embankment in the km 1,975 of R2 motorway was 46 % of design value. The measurements and predictions both show that the vertical drains significantly accelerated the rate of primary consolidation and that the magnitude of the increase was a function of the spacing of the drains.

5 ACKNOWLEDGEMENTS

This paper was supported by Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic, VEGA, grant project No. 1/0882/16.

6 REFERENCES

Correia G., Brandl H, and Magnan J-P: Earth and rockfill embankments for roads and railways: what was learned and where to go. Geotechnics of Roads and Railways (Eds: Brandl H, Adam D), Vol. 1, Wien: Österreichischer Ingenieur- und Architekenerein; 2014. p. 1–28.

Correia G, Winter, M.G. and Puppala. A. J.: A review of sustainable approaches in transport infrastructure geotechnics. Transportation Geotechnics, 7 (2016), pp. 21-28.

Moseley, M. P. and Kirsch, K.: Ground Improvement. 2nd editon, Taylor & Francis, 2004, 428 p.

Nguyen, G., Hrubešová, E. and Voltr, A.: Soil improvement using polyester fibre. Procedia Engineering, Vol. 111, 2015, pp. 596-600.

Priebe, H. J. (1995). The design of vibro replacement. Ground Engineering 28, No. 12, 31–37.

Khabiri M., M., Khishdari, A. and Ghebi E.: Effect of tyre powder penetration on stress and stability of the road embankments., Road Materials and Pavement Design, 18(4), pp. 966-979

Saberian M., Khotbehsara, M. M. and Jahandari, S., Vali, R., Li, J.: Experimental and phenomenological study of the effects of adding shredded tire chips on geotechnical properties of peat. International Journal of Geotechnical Engineering, 2017. 10 p.

Vaníček, M. and Vaníček, I.: Earth Structures: In Transport, Water and Environmental Engineering, Springer, 2008, 636 p.

Vaníček I. and Vaníček M.: Modern earth structures of transport engineering view of sustainable. 11th Int. Conf. on Modern Building Materials, Structures and Techniques, MBMST. Procedia Engineering 2013, 57:77–82.

Winter, M. G.: Construction on Soft Ground Using Lightweight Tyre Bales. In: Innovative and Sustainable Use of Geomaterials and Geosystems, ASCE Geotechnical Special Publication No. 245. Reston, VA: American Society of Civil Engineers; 2014. p. 1–8.

34


10 15 20 25

Bul

k de

nsit

y of

dry

soi

l (g

/cm

3 )

Moisture as % of dry soil weight

ρmax = 1.768 g/cm3

wopt = 15.2 %

1.800 1.750

1.700

1.650

1.600 1.550

QUALITY CONTROL OF CEMENT-IMPROVED SOIL

Le contrôle de la qualité du sol amelioré par le ciment

Monika Súľovská & Peter Turček Department of Geotechnics, Slovak University of Technology, Bratislava, Slovakia [email protected]

Zuzana Štefunková Department of Material Engineering, Slovak University of Technology, Bratislava, Slovakia

ABSTRACT: Middle plasticity clay was situated below the concrete floor of a storage hall. It was necessary to increase the bearing capacity and decrease the settlement of this soil layer. The 400 mm - thick layer of soil was improved by the addition of 5% cement. The static load tests showed that the required deformation modulus was not fulfilled. In the next step, the laboratory tests of Eoed using different initial cement content were executed. X-ray and DTA analyses of the cement content in the soil were also applied. The laboratory tests were aimed at identifying the properties of the improved clay after adding 3, 5, and 7% of cement to the varied moisture levels of the soil. The results of the compressibility of the unimproved and improved clay samples are presented in the paper.

RÉSUMÉ: L’argile de plasticité moyenne se trouvait au-dessous du plancher en béton du foyer. Il était nécessaire d’améliorer la capacité portante et de réduire l’abaissement de cette couche de sol. L’ épaisseur d’une couche de sol de 400 mm a été ameliorée par ajoutement du 5% ciment. Les essais de chargement statique ont montré que l’exigence du module de déformation n’a pas été respectée. Ensuite, les essais laboratoires Eoed avec ajoutement de la quantité variée du ciment dans le sol ont été executés. De même, l’analyse avec des rayons X et DTA a été apliquée afin de déterminer le contenu du ciment dans le sol. Les essais laboratoires ont été concentrés sur l’identification des propriétés de l’argile amelioré après addition du 3 – 5 – 7 % ciment en faisant varier l’humidité du sol. Le document présente les résultats des tests de compressibilité de l’argile amélioré et non amélioré. KEYWORDS: soil improvement, laboratory tests, compressibility of soil.

1 INTRODUCTION

The requirement to accelerate construction in unsuitable conditions (bad weather, degenerate soil conditions, etc.) leads many times to a need to improve the underlying layers of the structures. To solve these problems, technology similar to what is used to improve road construction is employed. Among the popular technologies is the addition of a certain percentage of cement into fine-grained soils. Mixing cement with soil and compacting it reduces the compressibility of the soil. The subsequent quality control of the improved soil is mostly achieved by static load tests.

Construction began on a large storage hall in Slovakia with an area of 100,000 m2 during the winter months. After the landscaping arrived, the climatic conditions unexpectedly worsened. In February, rainfall exceeded 300% of the long-term normal precipitation. The underlying layers of the future floors were improved during the rainy weather but were not protected. The adverse weather situation resulted in the suspension of work. The quality of the underlying layers was checked by static load tests after the layers had been improved. The results of the improved soil stabilization showed insufficient strength. After sampling, the properties of the original and improved soil were checked by laboratory tests.

2 LABORATORY ANALYSIS OF SOILS

Intact soil samples improved by cement were removed from the on-site construction of the factory buildings, as well as the original soil, which had not been improved by the cement. An analysis of the basic descriptive soil characteristics was conducted on the original soil samples. Based on Slovak standard STN 72 1001, the soil was classified as firm clay with a low degree of plasticity (F6 - CL). The original moisture of the

soil was more than 20%. The moisture of the improved soil with cement did not differ from the moisture of the original soil.

To determine the optimum moisture of the soil for compaction, the Proctor test (see Fig. 1) was used. The optimum moisture of the tested soil was determined to be wopt = 15.2%, which corresponded to the maximum dry density of soil ρmax = 1.768 g/cm3. The collected samples had a significantly higher moisture content than its optimal moisture should be.

Figure 1. Determination of the maximum bulk density and optimum moisture

3 OEDOMETRIC TESTS ON UNDISTURBED SOIL SAMPLES

A compressibility test using an oedometer was conducted on the original and improved soil too. As an improvement, 5% of cement was added to the soil. The results of the average deformation characteristics of the original and improved soil are collected in Table 1.

Based on the laboratory results, the following increase in the

35


0

5

10

15

20

25

30

13 14 15 16 17 18 19 20 21 22

Oed

omet

ric

mod

ulus

E

oed

(M

Pa)

Moisture of soil w (%)

Normal stress

10 - 25 kPa 25 - 50 kPa 50 - 100 kPa100 - 200 kPa

0

5

10

15

20

25

30

10 - 25 kPa 25 - 50 kPa 50 - 100 kPa 100 - 200 kPa

Oed

omet

ric

mod

ulus

E

oed (

MPa

)

Normal stress σ1 - σ2

Moisture of soil

w = 13.25 % w = 15.65 % w = 17.73 % w = 19.13 % w = 21.24 %

deformation characteristics was determined for the improved soil: • stresses in soil σ ≤ 50 kPa

326105

2532.

.

.

E

E

notoed

staboed==

• stresses in soil 50 ≤ σ ≤ 100 kPa

47.270.5

13.14==

notoed

staboed

E

E


58.162.9

19.15==

notoed

staboed

E

E

Note: Eoed, stab – oedometer modulus of the improved soil, Eoed, not – oedometer modulus of the original soil.

Based on the stress range of its own weight and the expected load from the buildings, the improvement of the soil after adding the cement was 1.5 to 2 times better. The recommended values of the deformation modulus of improved soil should not exceed Eoed = 14 MPa. Table 1. Deformation modulus of soils determined from compression tests

Normal stress Average modulus

σ1 − σ2 Improved soil Primary soil

(kPa) Eoed (MPa) Edef (MPa) Eoed (MPa) Edef (MPa)

10 − 25 35.73 16.79 3.84 1.81

25 − 50 32.25 15.16 5.10 2.40

50 − 100 14.13 6.64 5.70 2.68

100 − 200 15.19 7.14 9.62 4.52

4 COMPRESSION TESTS OF THE SOIL WITHOUT ANY IMPROVEMENT UPON COMPACTION, ACCORDING TO THE PROCTOR STANDARD

Artificially prepared samples of the soil, which was compacted according to the Proctor standard, were tested with the oedometer. The resulting average oedometer modulus corresponding to different moistures of the tested soils are evaluated in Table 2. Table 2. Average oedometer modulus of the tested soils at various moistures levels

Normal stress

Oedometer modulus Eoed (MPa)

σ1 − σ2 w = 13.25%

w = 15.65%

w = 17.73%

w = 19.13%

w = 21.24%

(kPa)

10 − 25 23.05 18.31 6.66 5.35 3.18

25 − 50 21.72 16.61 4.72 2.42 2.22

50 − 100 13.36 9.40 5.49 3.20 3.04

100 − 200 13.36 9.66 7.44 5.12 4.98

The effects of the changes in the soil moisture according to the oedometer modulus are shown in Fig. 2. The plasticity index of the soil was IP = 10 % (liquid limit wL = 30.5 % and plasticity limit wP = 20.5 %). When the soil was in its natural condition with a firm consistency, very small values of the deformation characteristics of the tested soil in all the extensities of the

normal stresses were found. When the soil stiffness was increased, it was possible to observe a decrease in the soil moisture below 17%. The consistency of soil at such a level of moisture was IC = 1.4. Decreasing the moisture below 17% significantly increases oedometer modulus of the soil.

Figure 2. Relationship between the moisture of the tested soil and the oedometer modulus

After the analysis shown in Fig. 2 and also taking into account Fig. 1, it can be stated that: • Exceeding the optimum moisture wopt occurred in samples

loaded by a normal stress of 50 kPa caused a rapid decreasing of Eoed.

• When the moisture increased, a significant decrease of Eoed of more than 5 times at a lower normal stress (< 50 kPa) was observed. When the value of the normal stress of 50 kPa was exceeded and the moisture was increased, a decrease of Eoed of approximately 3.5 times was determined.

Within the test range of the normal stress, Eoed was significantly affected by the moisture. Fig. 3 shows the relationship between the deformation characteristics and the normal stresses of the soil at various initial degrees of the soil moisture. Also, this evaluation proved the moisture around 17% as the limit value. At lower degrees of moisture, significantly different deformation parameters were detected, especially at a normal stress of up to 50 kPa.

5 IMPROVING THE SOIL CHARACTERISTICS BY ADDING CEMENT

The collected samples with a natural moisture of 20% indicated that the values of the deformation modulus of the original soil were very low. The addition of cement in the soil caused a decrease in the soil moisture, but the increase in the deformation parameters was not sufficient.

Figure 3. Dependence of normal stress and moisture on the deformation characteristics of the soil

36


0

10

20

30

40

50

60

70

80

90

100

110

10 - 25 kPa 25 - 50 kPa 50 - 100 kPa 100 - 200 kPa

Oed

omet

ric

mod

ulus

E

oed

(M

Pa)


Moisture of soil

w = 15.60 % + 5% of cement

w = 15.65 %

0

10

20

30

40

50

60

70

80

90

100

110

13 14 15 16 17 18 19 20 21 22 23 24 25

Oed

omet

ric

mod

ulus

E

oed (

MPa

)


Normal stress

10 - 25 kPa25 - 50 kPa10 - 25 kPa + 5% of cement25 - 50 kPa + 5% of cement

Very interesting results were obtained from an evaluation of the effect of the addition of 5% of cement (see Fig. 3). At a moisture level lower than 20.5% (a stiff consistency), a significant effect of the cement was observed. At the same time, the effect of the improvement increased with lower levels of the normal stress. It can be assumed that with an initial moisture content in excess of wopt + 5%, a significant decrease in the effect of the stabilization is to be expected. The resulting oedometer modules corresponding to the different moisture and cement contents in the tested soil are listed in Table 3. Table 3. Oedometer modulus of the soil improved by cement at various levels of moisture of the soil and cement contents

Normal stress

σ1 − σ2

(kPa)

Cement content

5% 3% 7%


15.60 17.95 24.56 14.10 14.27

Oedometer modulus of the improved soil Eoed (MPa)

10 − 25 101.26 36.04 6.04 31.06 93.61

25 − 50 43.85 13.22 2.70 17.84 43.11

50 − 100 20.98 10.83 3.31 18.51 24.37

100 − 200 18.71 10.37 3.90 18.66 24.06

The effects of the addition of 5% of cement in the soil on the

oedometer modulus at different levels of moisture are shown in Fig. 4. The results indicate that the impact on the cement by increasing the strength of the improved soil is limited by the degree of moisture. If the natural soil moisture content is less than 20.5%, this means that the soil has a stiff consistency, so the addition of the cement will result in increased strength. The effect of adding 5% of the cement content was reflected in the full range of the test load, but in varying degrees. The greatest rate of improvement was observed for loads up to 25 kPa.

Figure 4. Effect of addition 5% cement into the soil on Eoed at optimum degree of moisture Based on the laboratory results, the following increase in the deformation characteristics can be determined for the improved soil: • stresses in soil 10 ≤ σ ≤ 25 kPa

53.531.18

26.101%5==

notoed

staboed

E

E


94.261.16

85.48%5==

notoed

staboed

E

E


23.24.9

98.20%5==

notoed

staboed

E

E


95.16.9

71.18%5==

notoed

staboed

E

E

Note: Eoed, stab 5% – oedometer modulus of the improved soil with 5 % of cement,

Eoed, not – oedometer modulus of the original soil.

Assuming that a load is caused by objects, it is possible to expect an improvement in the properties of the soil by approximately 2 to 3 times over the soil without cement with the addition of 5% of cement at an optimum moisture. Increased moisture above the mentioned value w = 20.5% passes through the soil and forms a solid consistency. The impact of cementation on such a level of moisture is much lower or negligible. Fig. 5 indicates these results. The figure shows the dependence between the oedometer modulus of the soil with and without the added cement and the moisture at various loads. At higher values of normal stresses after exceeding the initial moisture, wopt + 5% reduces the effect of the added cement. Figure 5. Effect of moisture on the oedometer modulus for the soil without cement and the soil improved with cement

The cement added to the soil with a natural moisture content (which was between 19 to 21%) absorbed a portion of the water available for hydration. This effect will inevitably reduce the moisture of the soil itself. It is believed that an initial moisture content above the wopt + 5% should be expected to decrease in the stabilization effect. The laboratory tests showed one more interesting effect. The compressibility of the soil without the addition of the cement was less sensitive to the increase in the initial moisture. The same tendency was observed when increasing the normal stress on the soil.

The next step studied the reinforcing effect of the cement content of the soil. Tab. 3 shows the resulting values of the oedometer modules that were covered using three different amounts of cement. The treatment of this data is in Fig. 6, which graphically displays the effect of the cement content on the oedometer modules at different stages of loading. An important factor in this assessment is the virtually identical initial moisture of the samples.

Increasing the cement content in soil to 7% slightly increased the oedometer modulus at higher loads. However, this effect is not considered significant enough to make it worthwhile in many

37


0

10

20

30

40

50

60

70

80

90

100

110

10 - 25 kPa 25 - 50 kPa 50 - 100 kPa 100 - 200 kPa

Oed

omet

ric

mod

ulus

Eo

ed (

MP

a)


Moisture of soil and cement content

w = 15.65 % w = 15.60 % + 5% of cement w = 14.10 % + 3% of cement w = 14.27 % + 7% of cement

cases to increase the dose of cement. Reducing the cement content to 3% was reflected in a reduction of Eoed at lower loads (up to 50 kPa). For stresses ranging from 50 to 100 kPa, differences in the percentage of added cement are nearly negligible. The cement content in soil initially decreases the moisture content of the soil, but the cement absorbs the water and subsequently increases the strength of the soil. The results indicate that the cement content of 5% appears to be the most appropriate. Increasing the cement content is relevant only in the case of a higher load or in cases when the natural soil has a higher moisture content. Figure 6. Effect of cement content in soil on the oedometer modulus at various loads

6 THE QUALITY ASSESSMENT AND THE CEMENT CONTENT IN THE SOIL

The discussed cement and its contents were independently tested in stabilized soil. Laboratory tests of the physico-mechanical properties of the cement were carried out and supplemented by X-ray and DTA analyses. The stabilized soil was also investigated by DTA and X-ray analyses. The tested cement was used to stabilize the soil at the construction site. The properties studied and the results reached are as follows: After 28 days, the compressive strength reached 48.3 MPa. This value is in accordance with the requirements of the class of cement 42.5 MPa according to EN 197-1. • After 28 days, the compressive strength reached 48.3 MPa.

This value is in accordance with the requirements of the 42.5 MPa class of cement according to EN 197-1.

• The bulk density with a time deposit of the test samples slightly increased. After 28 days, the bulk density reached a value of around 2190 kg/m3, which corresponds to the standard values.

• After testing the cement slurry, it was found that the cement needs to reach a slurry of a normal density of 32% of the water.

• The initial setting of the cement slurry, which was observed after 195 minutes, fulfilled the limit set by the standard. The final setting occurred after 250 minutes.

• The soundness of the tested cement was 6.0 mm, which met the standard set limit of 10 mm.

• The bulk density of the fresh cement mortar was 2160 kg/m3. All the testing samples had a low scatter compared to the average.

• The X-ray analysis showed the incidence of cement clinker minerals as Alite - C3S (Tricalcium silicate), Belite - C2S (Dicalcium silicate), Brownmillerite - C4AF (Tetracalciumaluminoferrite), C3A (Tricalcium aluminate), and gypsum setting regulator (CaSO4.2H2O). Furthermore, Silica (SiO2), Calcite (CaCO3) and Portlandite Ca(OH)2 were observed. According to this composition, it can be assumed that this was Portland-composite cement CEM II.

The tests of the stabilized soil by the X-ray and DTA methods showed that the samples taken from the storage hall after the defective area of the static load tests contained less than 2% of the cement. By applying the same method to the artificially prepared samples, good agreement with the percentage of added cement was found.

7 CONCLUSION

Based on the compressibility tests of the stabilized soil, it is clear that the high moisture content of the soil after the rainy season decreased the soil parameters. The tests showed two reasons for the failure to achieve the criteria required for the static load testing. The first reason was the lower cement content as determined by the project. Instead of 5% of the cement, the samples taken from the subgrade at the construction site showed only a cement content in the range of 1 to 2%. Significant precipitation caused the natural soil moisture to exceed 20%. The laboratory experiments showed that at such a level of moisture of the unimproved original soil, the deformation properties of the soil were very low. The mixed cement decreased the soil´s moisture, but it reflected only a small increase in the Eoed. By adding cement, the deformation parameters of soil may increase 2-3 times. This effect is linked to the initial soil moisture before stabilization; the value wopt

should not be exceeded by 5%. Exceeding this level of moisture is not expected to have a major stabilization effect. 8 ACKNOWLEDGEMENTS This paper was created with the support of the Ministry of Education, Science, Research and Sport of the Slovak Republic within the Research and Development Operational Programme for the project “University Science Park of STU Bratislava”, ITMS 26240220084, co-funded by the European Regional Development Fund.

9 REFERENCES

Turček, P. – Súľovská, M. – Štefunková, Z.: Evaluation of soil layers improving below the production hall. SvF STU Bratislava, 2016, 3 p. (In Slovak)

Turček, P. – Súľovská, M. – Štefunková, Z.: Experimental research of deformation properties of fine-grained soil situated in hall subgrade. SvF STU Bratislava, 2016, 18 p. (in Slovak)

Turček, P. – Frankovská, J. – Súľovská, M.: Geotechnical design according to Eurocodes. 1th Ed., Bratislava, Engineering Advisory Centre of Slovak Chamber of Civil Engineers, 2010, 160 p. ISBN 978-80-89113-76-7 (in Slovak)

EN 197-1: Cement. Part 1: Composition, specifications, and conformity criteria for common cements. 2012. STN 72 1001: Classification of soil and rock in engineering geology and geotechnics. Slovak standard. 2010.

38


New effective construction management of the soft ground improvement

Il est nécessaire de prévoir le montant de l'affaissement à l'étape de remplissage antérieure plutôt que finale

Tae-Hyung Kim

Civil Engineering, Korea Maritime and Ocean University, Korea, [email protected]

Eun-Sang Im,

Infrastructure Researcher Center, K-water

Kwang-Yeol Lee

Civil Engineering, Dongseo University, Korea

Chang-Hoon Jung & Chang-Ho Kim

Korea Expressway Corporation

ABSTRACT: For an effective construction management of the soft ground improvement using the fill and vertical drain, there needs to be a way to predict the settlement based on the data measured at the earlier filling stage, rather than the final stage. A new method is able to predict the final settlement during the staged filling steps from any filling stage. To validate the proposed method, the settlement data measured in the field at a specific filling stage were analyzed to produce the soil parameters which are needed to predict the settlement in the new method. Then, using the obtained soil parameters, the settlement curve is predicted and compared with the measured one. The predicted settlement and the measured one are well matched. From the study, it can be confirmed that with the new method it is possible to predict settlement during the staged filling with only certain stage settlement data.

RÉSUMÉ : Il est nécessaire de prévoir le montant de l'affaissement à l'étape de remplissage antérieure plutôt que finale, pour une gestion éfficace de l'amélioration du sol mou à l'aide du remblais et des matériaux de drainage. Une nouvelle méthode peut prédire le montant de l'affaissement à toute étape du remblai dans le sol mou. Afin de vérifier cette méthode, on a estimé les paramètres du sol en analysant les données d'affaissement mesurées dans le champ à une étape de remplissage spécifique. Cette méthode qui a utilisé les paramètres du sol obtenus a prédit le montant de l'affaissement, et celui-ci a été comparé à la valeur mesurée. Celle-ci et l'affaissement prévu ont montré un bon accord entre eux. Cette étude nous amène à conclure que cette nouvelle méthode peut prédire le montant de l'affaissement pendant les étapes de remplissage avec les données d'affaissement mesurées à une étape de remplissage spécifique.

KEYWORDS Settlement, filling stage, soft ground, prediction, vertical drain.

1 INTRODUCTION

A series of construction managements are conducted in the soft ground improvement site applied filling and vertical drain (VD) to predict the final settlement. They are also used to correct the settlement predicted at the design stage, based on the measured settlement data. This is because there is a discrepancy between the settlement predicted at the design stage and the actual settlement. This discrepancy is caused by factors such as the heterogeneity of the in-situ soil, the determination problems of soil parameters used for analysis, the limits of theoretical solutions, and the variability of construction conditions.

To complement the discrepancy between the actual settlement and the predicted one, settlement prediction methods using measured data have been used extensively in practice. The hyperbolic method, Hoshino method, Monden method, and the Asaoka method are widely used in the field, and there has been a lot of research conducted on them (Tan et al., 1991; Chung et al., 2014; Edil et al., 1991).

The weak point of these methods is that they predict the final settlement only based on settlement data that was recorded after completing a certain stage fill (almost final stage) on the soft ground. For the construction of the embankment on the soft ground, most cases would plan the staged fill and load the ground gradually to secure the safety of the embankment, due to the low strength of the soft ground. Thus, for an effective construction management of the soft ground improvement using the fill and prefabricated vertical drain, there needs to be a way

to predict the settlement based on the data measured at the earlier filling stage, rather than the final stage. If the settlement can be accurately predicted according to the stage of fill, a reasonable construction management can be possible by effectively adjusting the filling period and the height.

A new method is proposed. This new method overcomes the weak point of the existing settlement prediction methods, and it can predict the final settlement as well as the settlement during the staged fill by using the settlement data measured at a certain staged fill. To validate the proposed method, the settlement data measured from a field improved with a prefabricated vertical drain in the mouth of Nakdong delta is used.

2 NEW METHOD

In a time-settlement relationship, the consolidation effect should account for the horizontal and vertical drainage. Nevertheless, the combined effects of consolidation are strongly dependent on the clay drainage depth and the drain spacing ratio. If the soft ground layer is thicker and the drain spacing is closer, the consolidation in progress is dominantly influenced by the horizontal drain, rather than vertical one (Lee and Chung, 2010). That is why the new method proposed in this study is primarily based on the horizontal consolidation solution by Barron.

)8

exp(1F

Tu h−

−= (1)

39


where Th is the horizontal consolidation time coefficient and F is the resistance coefficient as well as the sum of Fn, Fs, and Fr.

The relationship between the consolidation level and the settlement are given as follows.

)(fS

Su = (2)

where Sf is the final settlement and S refers to the settlement at an arbitrary time. Combining equation (1) and equation (2), the settlement S is expressed as equation (3).

−−=F

TSS hf

8exp1 (3)

The horizontal consolidation time coefficient (Th) and the final settlement (Sf) are given as follows.

2d

hhH

tCT = (4)

0

0log1 P

PPHe

CS cf

∆+

+= (5)

where Ch refers to the horizontal consolidation coefficient, t is time, Hd is backwater distance, Cc is compression index, e is the void ratio, H is the thickness of the soft layer, P0 is the initial effective stress and ∆P is the increasing stress (filling).

Equation (3) can be represented by substituting equations (4) and (5).

−−

∆+

+=

F

tC

HP

PPHe

CS h

d

cf 20

0 8exp1log

1

1

(6)

The settlement calculation equation (6) can be expressed at an arbitrary time in an exponential function using constant C1 and C2, as follows.

−−=

F

tCCCCS h

c 21 exp1 (7)

where, 0

0log1

1

P

PPHe

C c∆+

+= and

228

dHC −= .

The new method has the advantage of being able to reflect the site characteristics by incorporating the information obtained from the laboratory, in-situ test results, and the drain installation status which is not considered in the interpretation of the settlement in the existing methods.

C1 and C2 shown in equation (7) are constants which are calculated using in-situ experimental data. C1 is calculated based on the void ratio (e), the thickness of the soft ground (H), and the filling load (∆P). C2 is estimated based on the drain spacing ratio, drain installation equipment, drain installation depth, and the consolidation coefficient of the ground. Cc, Ch and F are the values estimated by conducting a back analysis technique through the new method on the monitored settlement data. The initial values of these are estimated based on the soil parameters obtained through the laboratory and in-situ tests.

While the existing prediction methods can only predict the final settlement the estimated Cc and Ch values using the

monitored data after a certain filling stage (usually final filling), they cannot reproduce the settlement curve during the stage of filling. The settlement curve according to filling stage is able to be predicted through the new method by using the estimated values of Cc, Ch and F. This feature is very important. The new method enables the prediction of not only the final settlement curve, but also the settlement according to the filling stage.

3 SITE APPLICATION

3.1 Description of site

The site area is located in the landfill area adjacent to the shoreline and in the mouth of the West Nakdong River. Starting from the Nakdong River, the northwest is a steep slope while the northeast is the mouth of the Nakdong River formed with alluvial delta. This stratum of ground is classified into the upper sand, cohesive soil, and the lower sand layers from the surface. The upper sand layer is composed of silt and clay, and the thickness is 5.2 ~ 11.9m. The value of N is about 0 ~ 24, which means it has a very loose to medium density, and is evenly distributed throughout the whole region. Cohesive soil is composed of silty clay with a thickness of 3.9 ~ 44.5m, and it is getting thicker in the southeast direction. The average N value is 0 ~ 5, which means it is very soft to very firm. The lower sand layer is composed of gravel sand, silty sand, and clay sand with a thickness of 1.0 ~ 22.0m. The N value is 0 ~ 44 indicating a very loose to dense state. Table 1. Soil properties at the site

Classification

Depth (m)

GL.(-) < 20

GL.(-) 20 ~ 25

GL.(-) > 25

Saturated unit weight γt (kN/m³) 16.6 16.1 18.0

Submerged unit weight γ′(kN/m³) 7.6 7.1 9.0

Specific gravity Gs 2.70 2.70 2.69

OCR 1.02 0.99 0.95

Compression index Cc 0.74 1.11 0.58

Recompression index Cr 0.09 0.13 0.07

Initial void ratio eo 1.59 1.80 1.08

Vertical consolidation coefficient Cv (cm²/sec) 1.5×10

-3 1.5×10

-3 3.0×10

-3

Horizontal consolidation coefficient Ch (cm²/sec) 3.0×10

-3 3.0×10

-3 6.0×10

-3

Horizontal permeability coefficient kh (cm/sec) 2.0×10

-7 2.0×10

-7 4.0×10

-7

Undrained shear strength Su (kPa) Su =14.95×Z+138.27

Strength increment ratio m 0.28

3.2 Final settlement prediction according to the stage of fill

In order to predict the settlement curve according to the stage of fill, using the new method, a reference stage for analysis must be selected first. For example, if three stages for an embankment construction are used in a site, then there are three choices for the references stage. Then, the soil parameters which are reflected in the site characteristics are needed. This data can be obtained from the laboratory and in-situ tests. Lastly, a PVD installation status is required. Using all of the selected data, C1 and C2 are calculated, while Cc, Ch and F are the values

40


estimated from conducting a back analysis through the new method on the monitored settlement data.

Figure 1 shows the settlement curves for the P-4 area in the site at each filling stage. The stages of A, B, and C are the first, the second, and the third stage of embankment, respectively. First figure is the settlement curve predicted by the settlement data monitored at the A filling stage. That is, the A stage is selected as the reference stage. Second and third figures are the settlement curves predicted by the settlement data monitored at the B and the C stages, respectively. Upon examining Figure, the predicted settlement curves are well matched with the monitored data for all stages. It is due to that in the P-4 area, that the settlement behavior for each filling stage tends to remain nearly constant.

Figure 2 shows the settlement curves for the P-19 area in the site at each filling stage. Like Figure 2, the stages of A, B, and C are the first, the second, and the third stages of embankment, respectively. First figure shows the settlement curve predicted by the settlement data that was monitored at the A stage of filling with actual data. Second and third figures are the settlement curves predicted by the settlement data monitored at the B and the C stages, respectively. Upon examining second and third figures, the predicted settlement curves are well matched with the actual data, because the settlement behavior for filling stage (B) is nearly the same as that of the filling stage (C). However, in viewing first figure, which is the predicted settlement curve based on the settlement data during the first A stage of filling, the settlement curves between actual and predicted are not well matched to each other. This is caused by the difference in the settlement behavior during stage A from that of stage B and C. In addition, the monitoring time during stage A is too short of a period, which means the monitored

settlement data is not enough for analysis.

Hei

gth

(m

)

2

4

6

8

Sett

lem

en

t (c

m)

0

50

100

150

200

P-4 Field Data(PBD : 2.0m)

Predicted Values at A Stage

A Stage

B Stage

C Stage

Time (Day)

0 200 400 600 800 1000 1200 1400

Sett

lem

en

t (c

m)

0

50

100

150

200

Predicted Values at C Stage

Sett

lem

ent

(cm

)

0

50

100

150

200

Predicted Values at B Stage

Figure 1. Comparisons of time - settlement curves between measured and predicted by new method at P-4 area in the site.

Hei

gth

(m

)

2

4

6

8

Sett

lem

en

t (c

m)

0

50

100

150

200

P-19 Field Data(PBD : 2.0m)

Predicted Values at A Stage

A Stage

B Stage

C Stage

Time (Day)

0 200 400 600 800 1000

Sett

lem

en

t (c

m)

0

50

100

150

200

Predicted Values at C Stage

Set

tlem

ent

(cm

)

0

50

100

150

200

Predicted Values at B Stage

Figure 2. Comparisons of time - settlement curves between measured and predicted by new method at P-19 area in the site.

4 CONCLUSION

This study proposed a new method, which is able to predict both the final settlement and the settlement during the staged filling steps from any filling stage. To verify the new method, the settlement data obtained at the field located at the mouth of the Nakdong River was used.

From the comparison results of both the predicted and the actual settlement data, it can be concluded that the new method can successfully predict the settlement curve at any filling stage, but only if the settlement behavior for each filling stage tends to remain fairly constant and the monitoring time during each filling stage is enough to obtain sufficient settlement data for analysis.

5 REFERENCES

Arulrajah, A., Nikraz, H., Bo, M.W., 2004. Factors affecting field instrumentation assessment of marine clay treated with prefabricated vertical drains, Geotext. Geomembrs, 22 (5): 415-437.

Bo, M.W., Chu, J., Low, B.K., Choa, V., 2003. Soil improvement : prefabricated vertical drain techniques, Thomson Learning Asia, Singapore, 341 p.

Chung, S.G., 1999. Engineering properties and consolidation characteristics of Kimhae estuarine clayey soil, Proc., 11th ARC on SMGE, Special Publication on Thick Deltaic Deposits, ATC-7 Workshop, Seoul, 93-108.

Chung, S.G., Kweon, H.J., Jang, W.Y., 2014. Observational method for field performance of prefabricated vertical drain, Geotextiles and Geomembrane, 42 (4): 405-416.

Lee, N.K., Chung, S.G., 2010. Reevaluation of the factors influencing the consolidation of ground by incorporating prefabricated vertical drains, KSCE J. Civ. Eng., 14 (2): 155-164.

Tan, T.S. Inoue, T., Lee. S. L., 1991. Hyperbolic method for consolidation analysis, Journal of Geotechnical Engineering, ASCE, 117 (11):1723-1737.

41

An Analysis Model of PDV-installed Deposit Consolidation Considering Varied Discharge Capacity with Depth

Ba-Phu Nguyen

Department of Ocean Engineering, Pukyong National University, Busan, 608-737, Republic of Korea

Yun-Tae Kim

Department of Ocean Engineering, Pukyong National University, Busan, Republic of Korea, Email: [email protected]

EXTENDED ABSTRACT

It is well known that consolidation rate of prefabricated vertical drain (PVD)-installed ground is closely related to the discharge

capacity (qw) of PVD, which decreases with increasing effective stress. Many theoretical and experimental researches combined with

field practices indicated that the discharge capacity variation of prefabricated vertical drain with depth significantly influenced to

excess pore water pressure dissipation or settlement rate (Hansbo 1981; Hansbo 1983; Rixner et al. 1986; Deng et al. 2013). Hansbo

(1983) and Rixner et al. (1986) presented similar results from vertical discharge capacity tests. Figure 1 shows that qw decreased

nonlinearly with increasing lateral confining stress.

0

500

1000

1500

2000

2500

0 100 200 300 400 500 600 700

Dis

ch

arg

e c

ap

acity, q

w(m

3/y

ea

r)

Lateral confining pressure (kPa)

Geodrain (1)Geodrain (2)

Alidrain

Colbond

Mebradrain

Mebradrain

MD7407 (4)

Castle Drain

Board (4)Colbond CX-1000 (1)

Colbond

CX-1000 (4)

Figure 1. Variation of vertical discharge capacity with confining stress (after Hansbo 1983 and Rixner et al. 1986)

In analytical solution of Hansbo’s approach, qw was held constant with depth, which is no true in the field case. Deng et al.

(2013) assumed that discharge capacity decreased linearly with depth and was expressed as:

1 2( )wz wo

zq q A A

L (1)

The simultaneous assumption of two parameters (A1, A2) is somewhat inconvenient when analyzing the consolidation behavior

of a PVD-improved soil deposit. In this study, we further assume that discharge capacity decreased nonlinearly with an increase in

depth, which results in an increase lateral confining pressure.

2

1wz wo

zq q A

L

(2)

In above Equations, qwo is discharge capacity at ground surface (z=0); A1, A2 and A is constant; L is PVD length in PVD-improved

42

zone. The formulation of the analytical solution for the average excess pore pressure of axisymmetric unit cell considering nonlinear

distribution of discharge capacity of PVD was solved. The solution was based on Hansbo’s procedure. The average excess pore

pressure can be described following:

18 /hT

r ou u e

(3)

where

2

1 2

w

123ln ln ln

4

h h

s o

Az Ak k Ln Ls

s k L Az L Azq A

(4)

The comparison of the degree of radial consolidations for different distribution of discharge capacity was carried out. The

results shows that the degree of radial consolidation of nonlinear distribution of discharge capacity was significant delayed, compared

with the constant case linear distribution case and the delay of consolidation rate is more obvious at a deeper depth, as shown in

Figure 2.

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10

Degre

e o

f ra

dia

l consolid

ation

(Ur%

)

Time factor (Th)

qw is constant (Hansbo 1981)

linear distribution (A1=1;A2=0.9)

Parabolic distribution (A=0.9)

qw = constant

Linear distribution with A1 = 1, A2 = 0.9

Nonlinear distribution with A = 0.9

Figure 2. Comparison of horizontal degree of consolidations for different distributions of discharge capacity

REFERENCE

1. Hansbo, S. 1981. Consolidation of fine-grained soil by prefabricated drains. Proc., 10th Int. Conf. Soil Mech. and Found. Eng., (3),

677-682

2. Deng, Y.B., Xie, K.H., Lu, M.M. 2013. Consolidation by vertical drains when the discharge capacity varies with depth and time.

Computers and Geotechnics, (48): 1-8

3. Rixner, J.J., Kraemer, S.R., and Smith, A.D. 1986. Prefabricated vertical drains. Engrg. Guidelines, FWHA/RD-86/168, Vol. I, Federal

Highway Administration, Washington.

43


Determination of bearing pressure of soil at the Abu-Dhabi Plaza construction site in Astana by a plate load test

L'évaluation de la capacité portante du sol par un essai de charge de plaque sur le site de construction

Plaza Abu-Dhabi à Astana

Askar Zhussupbekov,

Department of Civil Engineering, L.N. Gumilyov Eurasian National University, Kazakhstan, [email protected]

Abdulla Omarov,

Department of Civil Engineering, L.N. Gumilyov Eurasian National University, Kazakhstan

Ivan Morev,


Gyulnara Zhukenova,


Gulzhanat Tanyrbergenova


ABSTRACT: To prevent a tragic accident and for ensuring a safety at the construction site, when a heavy crane install and work, such as the TEREX C 6800 should assess the bearing capacity of the soil for control the ground pressure. That work carried out at a construction site of Abu-Dhabi Plaza project for prediction the ground pressure to design of temporary working place for heavy crawler crane. Among all field tests the Plate Load Test (PLT) is the best in simulation the vertically loaded soils behavior and is used for determining the ultimate bearing capacity of the soil ground and a settlement under loading. In this paper the plate load test is carried out in accordance with GOST 20276-99 “SOILS. Field methods for determining the strength and strain characteristics”. It consists of step loading a steel load plate of 300mm diameters and records the settlements corresponding to each load increment. RÉSUMÉ : Pour éviter un accident tragique et pour assurer une sécurité au chantier, lorsqu'une grue lourde installation, comme le TEREX C devrait évaluer la 6800 capacité portante du sol pour le contrôle de la pression au sol. Ce travail effectué sur un chantier de construction du projet d'Abou Dhabi Plaza par notre équipe pour prédire la pression au sol pour la conception du lieu de travail temporaire pour grue sur chenilles lourd. Parmi tous les essais sur le terrain, le test de charge de plaque (PLT) est le meilleur dans la simulation du comportement des sols chargés verticalement et est utilisé pour déterminer la capacité de support ultime du sol et un établissement en cours de chargement. Dans cet article, le test de charge en plaque est effectué conformément à GOST 20276-99 "SOLS". Méthodes sur le terrain pour déterminer les caractéristiques de résistance et de contrainte ". Il se compose de l'étape du chargement d'une plaque de charge en acier de 300 mm de diamètre et enregistre les colonies correspondant à chaque incrément de charge.

KEYWORDS: Plate load test (PLT), bearing capacity, load – settlement, silty clay.

1 INTRODUCTION

Many megaprojects are being built in Astana. One of the unique projects is the “Abu-Dabi Plaza” complex which was started to the construction from July,1 2011 in Astana. This will be the highest building in Central Asia. "Abu-Dabi Plaza" - a complex from several towers, united around the main building with a height 382 meters - 88 floors here are used several heavy crane for construction stage (see Figure 1). The purpose of this study is a determination of bearing capacity of soil on construction site where will be installed heavy cranes Terex CC6800 and Liebherr LTM1500 which shall erect in-situ structures. A plan of location of crane at construction site was design by the Arabtec Consolidated Contractors Limited Company. That company appointed the depth and location of geological boreholes for geotechnical investigation. According to site description yellowish-brown, moist, silty, very stiff clay is identified in the first depth 2 m. Clay has

medium-high plasticity. Clay below 1.5-1.8 m is medium stiff. The groundwater in boreholes not found.

Figure 1. Project Abu-Dhabi Plaza in Astana

44


Figure 2. Design information about the ground pressure from crawler crane TEREX CC6800 at the construction site Abu-Dhabi Plaza

By the calculation at the preliminary design stage ground bearing pressure are up to 14 ton/m2 or 140 kN/m2 below mats and 330 kN/m2 below crawlers. This should be checked using a plate load test to determine the bearing capacity of the soil.

2 SOIL PROPERTIES

Laboratory tests were performed on representative samples obtained from boreholes including natural moisture content, Atterberg Limits, density of soil, strength and deformation properties. Soil mechanics laboratory test results are summarized in the Tables 1 and 2.

Table 1. Soil mechanics laboratory test results on EGE -1 – Silty clay

Bor

hole

ID

Dep

th o

f sa

mpl

ing

(m

)

Atterberg limit (%)

Wat

er c

onte

nt

(%

)

Nat

ural

den

sity

of

soil

, g/

cm3

USC

S c

lass

ific

atio

n

LL PL IP w ρ

BH-1 0.5 24.0 9.0 15.0 8.9 1.99 CL

1.3 27.0 15.0 12.0 15.7 1.96 CL

BH-2 0.5 23.0 9.0 14.0 8.6 2.02 CL

1.5 25.0 14.0 11.0 16.3 1.97 CL

BH-3 0.5 22.0 8.0 14.0 7.9 2.0 CL

1.5 28.0 18.0 10.0 17.2 1.95 CL

BH-4 0.5 26.0 11.0 15.0 10.8 2.03 CL

1.5 29.0 17.0 12.0 19.6 1.98 CL

Quantity of definitions 8

Average 25.5 12.6 12.9 13.1 1.99

MIN 22.0 8.0 10.0 7.9 1.95

MAX 29.0 18.0 15.0 19.6 2.03

Table 2. Strength properties of soils on EGE -1 – Silty clay

Borhole ID

Depth of sampling (m)

Angle of internal friction (degrees)

Cohesion (kPa)

Deformation Modulus

(MPa)

BH-1 0.5 24 19 8.6 1.3 20 14 7.4 BH-2 0.5 22 20 8.1 1.5 19 16 7.2 BH-3 0.5 26 21 7.9 1.5 21 18 6.8 BH-4 0.5 20 17 7.6 1.5 18 15 7.1 Quantity of definitions 8 8 8 Average 21 18 7.59 MIN 18 14 6.8 MAX 26 21 8.6

3 PLATE LOAD TEST

For deriving setlement and strength properties, the equipment with circular plate 300 mm dia. of Controls group, Italy has been used on this site. The plate for testing rigid to avoid bending and nominally flat on the bottom (see Figure 3). To achieve a close contact of the soil with the circular plate, the plate turns twice around its vertical axis, and changing the direction for second rotation. After installing the plate is checked its horizontal position. A procedure of load test consists following: 1) Maximum pressure under the plate apply up to 0.5 MPa (50 ton/m2); 2) Applied Pressure to each load increment are: 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 MPa. Unloading occurs after loading 0.5 MPa, next unload are 0.3 MPa and 0 MPa. 3) Each load increment is continued until the stabilization of plate settlement – no more than 0.1 mm in the last hour of observation. 4) Settlement value are readed on the dial gauges every 15 minutes during the first hour of test, every 30 minutes during the second hour, then in a 1 hour before the stabilization of the soil deformation. Total quantity of load tests at construction site: a Plate Load Test 1 (further PLT-1) and Plate Load Test 2 (further PLT-2), and Plate Load Test 3 (further PLT-3) had been made (see Figure 4). According to the results of each plate load test are draw a loading and unloading curves and all test data are included in a Table 3.

Figure 3. Scheme of the installation of equipment for plate load test

1 – load plate 300mm dia; 2 – dial gauges 30 mm travel 0.01 mm divisions; 3 – hydraulic jack; 4 – digital pressure gauge 0 to 0.8 MN/m2; 5 – hydraulic pump; 6 – extension rods; 7 – ballast for the reaction.

45


Figure 4. The Plate load test (PLT) at construction site Abu-Dhabi Plaza

Table 3. Processed data of the PLT test performed with a 300 mm dia. plate in a natural silty clay

Num

ber

of lo

ad/

unl

load

ste

p

Pres

sure

to th

e pl

ate

(MPa

) an

d L

oad

(ton

/m²)

Settlements (mm) (average 3 dial gauge readings)

Loa

ding

Tim

e (m

in)

Dur

ing

the

load

ap

plie

d (m

m)

Dur

ing

load

cre

ep

(mm

)

Tot

al

sett

lem

ent

(mm

)

1 2 3 4 5 6 PLT-1

Loading

1 (0,05) 5 0.25 0.39 0.64 90

2 (0,1) 10 0.28 0.27 1.19 90

3 (0,2) 20 0.72 0.48 2.39 90

4 (0,3) 30 0.84 0.43 3.66 90

5 (0,4) 40 0.73 0.53 4.92 90

6 (0,5) 50 0.84 0.75 6.51 120

Unloading

1 (0,3) 30 0.04 0.01 6.46 15

2 (0,1) 10 0.96 0.07 5.43 15

3 0 0.75 0.04 4.64 60 PLT-2

Loading

1 (0,05) 5 1.89 0.55 2.44 90

2 (0,1) 10 1.07 1.22 4.73 90

3 (0,2) 20 2.47 2.81 10.01 120

4 (0,3) 30 1.63 3.14 14.78 120

5 (0,4) 40 1.51 2.50 18.79 180

6 (0,5) 50 0.6 3.09 22.48 180

Unloading

1 (0,3) 30 0.03 0.02 22.43 15

2 (0,1) 10 0.05 0.04 22.34 15

3 0 0.61 0.35 21.38 60 PLT-3

Loading

1 (0,05) 5 0.22 0.32 0.54 90

2 (0,1) 10 0.32 0.14 1.00 90

3 (0,2) 20 0.72 0.12 1.84 90

4 (0,3) 30 0.60 0.11 2.55 90

5 (0,4) 40 0.44 0.11 3.10 90

6 (0,5) 50 0.33 0.13 3.56 90

Unloading

1 (0,3) 30 0.02 0.01 3.53 15

2 (0,1) 10 0.15 0.02 3.36 15

3 0 0.50 0.09 2.77 60 Note: (0,05) 5 : (0,05) - Pressure to the plate (MPa); 5 - Load (ton/m²)

Results of test are presented in graph form in Figure 5 and show relationship among load-time-settlement and to predict of subgrade modulus.

Figure 5. Load-settlement diagram from PLT test

4 CONCLUSION

Factors to be considered by the engineer include number of tests needed at the site, load range, size of the plate, and a settlement. Soil conditions were natural at the time of conduction each of the tests. Locations of each test pointed by a Representative of the Client company. From results of Plate load test № 1 - the settlement at the maximum applied load 0.5 MPa (50 ton/m2) is 6.51 mm; Plate load test № 2 - the settlement at the maximum applied load 0.5 MPa (50 ton/m2) is 22.48 mm; Plate load test № 3 - the settlement at the maximum applied load 0.5 MPa (50 ton/m2) is 3.56 mm. On the results PLT-2 test the place needed to improve soil ground by compaction with gravel materials. Elasticity modulus from PLT for silty clay is finded E=21-38 MPa. The total value of load on the plate in such a stage divided by the area of the steel plate gives the value of the ultimate bearing capacity of soil.

5 REFERENCES

GOST 20276-99, 1999. Soils. Field methods for determining the strength and strain characteristics. Gersevanov Research Institute of Bases and Underground Structures (NIIOSP), Moscow.

46


Offered methods for the determination of bearing capacity of pile regarding types of foundation of Astana city

Propositions pour la détermination de la capacité d'appui de la pile concernant les types de fondation de la ville d'Astana

A.Zh.Zhussupbekov, N.T.Alibekova, A.S.Tulebekova & N.A.Toleubay Department of Design of buildings and constructions, L.N. Gumilyov Eurasian National University, Kazakhstan,

[email protected]

Zh.N.Ospanova Department of Technology of industrial and civil construction, L.N. Gumilyov Eurasian National University, Kazakhstan

N.N.Satan Department of Building materials and technology, Karaganda State Technical University, Kazakhstan

D.Khussainova Department of Civil Engineering, Nazarbayev University, Kazakhstan

ABSTRACT: The paper presented methods of determine of bearing capacity of pile: analytical method and experimental method. Discussion of using technological features, advantages and disadvantages of methods. The paper include method of determine bearing capacity of pile in problematical soil ground of Astana city. The analysis are presented that new method of determine of bearing capacity of pile gives detailed information about the process testing and makes more reliable results. And so researcher of advanced pile technologies is very important for the feature Kazakhstan geotechnic development.

RÉSUMÉ : Le document a présenté des méthodes de détermination de la capacité de tas de la pile: méthode analytique et méthode expérimentale.Discussion sur l'utilisation des caractéristiques technologiques, des avantages et des inconvénients des méthodes. Le document comprend une méthode de détermination de la capacité de palier de la pile dans les sols problématiques de la ville d'Astana. L'analyse est présentée dans le document montre que la nouvelle méthode de détermination de la capacité de tas de pile fournit des informations détaillées sur les tests de processus et donne des résultats plus fiables. Et donc le chercheur des technologies de pilotes avancées est très important pour la fonctionnalité du développement géotechnique du Kazakhstan.

KEYWORDS: pile, test, bearing capacity, method.

1 INTRODUCTION

Experience driving the piles, saved up lately, and results of their tests testify that designers overestimate length of piles on the average for 1-2 m that causes additional rise in price connected with necessity cutdowm sticking out goals by means of specially created mechanisms, and sometimes even manually. Tests of such piles «not finished» up to design marks show their quite sufficient bearing capacity (Narbut 1972).

As bearing capacity of a pile define not only a limiting condition of a material of a pile or a ground near it, but also the size of the loading corresponding admissible settlement for certain type of a construction. At that bearing capacity of a pile on soils depends on mechanical properties of soils and from a method of the device or immersing of a pile. And on a fuctioning of a pile under action of static loading the big influence is rendered with the changes occuring in the surrounding ground at driving of piles (Pilyagin A.V. and

Glushkov V.E. 1989). Besides, the numerous researches lead by various authors,

have shown, that at driving piles irrespective of depth immersing in the multilayered basis the condensed sandwich shell is formed

As at immersing a pile in sand around of it there are ring condensation in radius of 2-6 diameters of a pile depending on personal density of soils. Under an edge of a pile the condensed zone extends on depth equal 2 diameters of a pile.

And at driving piles in clay soils the pile at immersing moves apart soil, and the edge forms the condensed zone in the form of a wedge which depends on property of soil and from depth of immersing of a pile. The condensed zone under influence of resistance of underlaying layers gradually is pushed out from under an edge of a pile and placed around its lateral surface, forming a concentric environment which thickness will decrease until all stock of the grasped ground will not be spent.

Besides at driving piles in clay soils there is a sharp decrease in durability of a ground in connection with redistribution of water in times of soil and destruction of structural communications. Then during rest it is observed thixotropycal hardening of these soils, that conducts to increase in bearing ability of piles. Hardening is connected with process of redistribution of a moisture. Water environments around of the particles which are settling down about piles, gradually resolves, causing increase of durability coagulation communications and by that soil. In time this process proceeds differently, depending on features of soils, but gradually it fades. The increase in bearing capacity of the piles shipped in sandy loams, practically comes to an end later 5 days, in loams basically in 15 days, in clay 25-30 days.

During «rest» within the limits of the specified terms bearing capacity of piles raises quickly enough, and then increase hardening of soil occurs already so slowly, that it seldom has practical value.

47


The account of «rest» allows to define more precisely bearing capacity of piles and enables to appoint higher calculation resistance.

For a correct estimation kinetics increases in bearing capacity of the piles, shipped in soil, huge value the has method of its definition, in some cases even influencing on size of bearing capacity (SNIP RK 2002).

2 METHODS FOR DETERMINE THE BEARING CAPACITY OF PILE

Existing methods of definition of bearing ability of piles are divided in two basic groups:

1) the analytical methods using the theories of limiting balance, the theory of elasticity and model linear deformations of soils.

2) the experimental methods based on field tests, to which concern penetration (static and dynamic), static and dynamic tests of piles, tests of soils reference piles, pressing tests.

2.1 Analytical methods of definition of bearing capacity of piles

At an estimation of bearing ability of piles calculation on two groups of limiting state: on bearing capacity (I group) when the maximum load on a pile is calculated, and on deformations (II group) when loading on a pile depending is defined on its settlement (Citovich N.A. 1979, Dalmatov B.I. 2000).

In many methods bearing capacity is characterized as the sum of resistance under the bottom end and on its lateral surface (see Figure 1). For the first time such approach at an estimation of a maximum load on a pile has been made by Patton in 1895, and till now this way applied in native and foreign normative documents.

Figure 1. Scheme of work of a trailing pile under loading.

At a stage of design engineering the method of definition of bearing capacity of piles in conformity with SNIP RК 5.01-03-2002 under the following formula is widely used:

iicfн

cRcd hfuARF , (1)

where с - factor of operating conditions of a pile in soil, accepted equal 1;

пR - calculation resistance of soil under the bottom end of a pile, kPа, accepted with normative table 1 (SNIP RK 2002).;

A - the area lean on a soil of a pile, м2, accepted on the area of cross-section section of a pile gross or on the area of cross section unpleasant enlargement on its greatest diameter, or on the area of a pile-environment net;

U - external perimeter of cross section of a trunk of a pile, m;

if - calculation resistance i layer of a soil on a lateral surface of a pile, kPа, accepted under normative table 2 (SNIP RK 2002).;

ih - thickness i layer of the soil adjoining a lateral surface of a pile, m;

сR and cf - factors of operating conditions of a soil accordingly under the bottom end and on a lateral surface the piles considering influence of a way of immersing of a pile on calculation resistance of a soil and accepted with normative table 3 (SNIP RK 2002).

The structure of the formula (1) precisely enough reflects a fuctioning of piles in a soil and is calculated as the sum of resistance of soils under its bottom end and on a lateral surface. However, definition by this way of limiting resistance approximately as it is difficult to divide lateral and frontal resistance which are shown in full interrelation. Average skilled data normative specific frontal пR and lateral if not always answer real conditions and depend on geological conditions of a platform which can strongly change during construction.

As tables of settlement resistance in SNiP RК 5.01-03-2002 are received on the basis of processing results of tests more than 200 piles of the various kinds lead by Luga А.А., and as calculation the guaranteed least values of the given tests have been accepted. Therefore in this case results of calculations of bearing capacity of trailing piles by technique SNiP give a greater deviation from really received results, especially on weak soils.

Besides at purpose of normative sizes пR and if are not considered possible change of humidity of soils as a result of construction of a building as the specified parameters only depend on a parameter of fluidity (consistence) LI . As these characteristics (humidity of a ground, a consistence) rather essentially change even within the limits of one investigated thickness. Especially more mistakes arise at reception of settlement characteristics at small volume of researches, and the error can result as in overestimate of settlement characteristics, and understating. Therefore, the bearing capacity, determined by the calculation, requires comparison with the results of practical material obtained by field tests of piles.

2.2 Field tests of piles for bearing capacity

At designing the piles foundationss by one of the most widespread and effective methods of definition of bearing capacity is static penetration (Figure 2) (Mariupolskiyi L.G. 1984, Trofimenkov U.G. and Vorobkov L.N. 1974).

1 - screw anchoring piles; 2 - a frame; 3 - a probe; 4 and 5 - dynamometers; 6 - a jack; 7 - directing

Figure 2. Scheme of immersing of a probe at static penetration.

48


For the first time the method of definition of bearing capacity of piles according to static sounding has been regulated by native norms in 1987 (SNiP II-Б.5-67). In the further, on the basis of the lead researches, the method has been specified for various types of probes and kinds of soils (GOST 2001).

Carrying out of field test of soils is regulated by static penetration GOST 19912-2001 (GOST 2001).

At that static penetration is applied to test not frozen and thawed sandy-clay soils, 10 mm are larger than 25 % of particles containing no more.

And for research of the sandy-clay strains containing no more of 40 % coarsefragmental of a material, on depth up to 20 m dynamic penetration (Figure 3) is intended.

1 - a conic tip; 2 - a bar of a probe; 3 - an anvil; 4 - hammer;

5 - capture of hammer; 6 - the terminator of height of rise of hammer Figure 3. Scheme of installation of dynamic penetration.

By means of this method it is possible: - to dismember a cut of breeds on the layers, differing

resistance dynamic penetrаtion with high accuracy (up to 0.05); - to establish their degree of uniformity, to define parameters

of some properties and depth driving piles. Carrying out of the given field test of soils also is regulated

GOST 19912-2001 (GOST 2001). But as practice of designing of the pile bases bearing

capacity of piles certain by results of static and dynamic penetration on 25 % on the average above bearing capacity certain by calculation and more reliable results of bearing capacity of pile can be received at carrying out static test (Figure 4). However, the quantity of predesign static tests of trial piles is very limited 2-4 piles for a quarter in connection with high expenses at carrying out of the given tests.

Figure 4. Test by static loadings.

In this connection apply more mobile and not demanding high expenses a dynamic test method of piles which is applied to any kinds of piles, irrespective of their bearing capacity is more often, does not damage working capacity of piles and guarantees reception of the most exact information on bearing capacity of a pile (Figure 5). Besides the given test allows to estimate approximately uniformity soils the bases, revealing sites, described in various density and as to specify length of a pile (GOST 1994).

Figure 5. Test by dynamic loading.

3 METHOD OF DETERMINE BEARING CAPASITY OF PILE IN PROBLEMATICAL SOIL OF ASTANA

Based on the results of static tests of piles carried out on construction sites in Astana, the bearing capacity of piles, brought to an unloading draft of 6 mm (BS 1996 and BS EN 1997), corresponds to results bearing capacity of pile at dynamic tests of piles, apparently from the schedule. Therefore calculation bearing capacity of piles has been compared to results of dynamic tests of pile taking into account types of the bases (Figure 6) (Zhusupbekov 2011)..

As a result of the analysis it has been established, that bearing ability of piles at static tests dF in 98 cases (79 %) was more loading c

dF transferred to a pile at construction. The deviation dF from c

dF no more than on 10 % (both sides) has been noted 24 piles (19 %) and only in 33 cases (26 %) the deviation has made no more than 20 %. At 67 piles (54 %) value of bearing capacity at dynamic tests the loadings transferred pile at construction (Figure 6). Hence, the given bases have greater and unjustified stocks.

In addition, reliability coefficients were established for all tested piles, taking into account the type of the base (see Figure 7), on the basis of comparing the values of the dynamic tests with the estimated values of the bearing capacity in accordance with SNiP RK 5.01-03-2002 (see Table 1 and Figure 8), which take into account the working conditions of the pile in the ground.

49


Fd =Fdp

y = 1,1x

y = 0,9x

y = 1,2x

y = 0,8x

0,0

200,0

400,0

600,0

800,0

1000,0

1200,0

1400,0

0,0 200,0 400,0 600,0 800,0 1000,0 1200,0 1400,0

Fdp

Fd

Figure 6. Comparison of values of loading at construction with sizes of bearing capacity on static tests of piles.

1 type 2 type 3 type 4 type 5 type 6 type 7type 8 type EGE-1 EGE-1 EGE-1 EGE-1 EGE-1 EGE-1 EGE-1 EGE-1 EGE-2а EGE-2d EGE-2а EGE-2 EGE-2а EGE-2а EGE-2а EGE-2d EGE-4 EGE-2а EGE-3а EGE-3а EGE-3b EGE-2b EGE-2b EGE-2а

EGE-4 EGE-4 EGE-3b EGE-3c EGE-4 EGE-3а EGE-3а EGE-3c EGE-5 EGE-3b EGE-3b EGE-4 EGE-3c EGE-3c EGE-4 EGE-4

Figure 7. Zoning of the territory of Astana city according to foundation types.

Table 1. Value of factor of reliability calculations of bearing capacity

dсdd FFK

Types of basis

1 2 3 4 5 6 7 8

Value of factor

of reliability

dсdd FFK

1,22 1,23 0,81 0,85 0,91 1,00 1,02 1,03

Number of tested

piles 103 14 64 184 91 34 26 13

type 1

Kd = 1,22

type 3

Kd = 0,81

type 4

Kd = 0,85

type 2

Кd = 1,23

type 5

Kd = 0,91

type 7

Kd = 1,02

type 6

Kd = 1,00

type 8

Kd = 1,03

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0

Fdc, kN

Fd, kN

Figure 8 Comparison of values of dynamic tests with calculation sizes on SNiP RК 5.01-03-2002 taking into account types of basis

4 CONCLUSION

The analysis in the article shows that the method of determine of bearing capacity of pile makes more reliable and gives detailed information about the process of testing and the results. Actual question today is to update the national standards, harmonization with international standards. The method which described is very important for the feature Kazakhstan geotechnical development.

5 REFERENCES

Narbut R.M. 1972. Rabota svay v glinistykh gruntakh. Stroyizdat, Leningrad.

Pilyagin A.V. and Glushkov V.E. 1989. Sravneniye raschetnykh i fakticheskikh osadok svaynykh fundamentov iz piramidal'nykh svay. Materialy nauchno-tekhnicheskogo seminara «Ispol'zovaniye naturnykh nablyudeniy dlya sovershenstvovaniya proyektirovaniya fundamentov i izyskaniy v usloviyakh slabykh gruntov.: LDNTP, Leningrad. 36-47.

SNIP RK 5.01-03-2002. Pile foundation. Citovich N.A. 1979. Mekhanika gruntov (kratkiy kurs). Moscow. Dalmatov B.I. 2000. Mekhanika gruntov, 204. Mariupolskiyi L.G. 1984. Kompleksnoye issledovaniye gruntov dlya

proyektirovaniya i stroitel'stve svaynykh fundamentov. Osnovaniya, fundamenty i podzemnyye sooruzheniya: Trudy NII osnovaniy. Stroyizdat, Moscow. 56-65.

Trofimenkov U.G. and Vorobkov L.N. 1974. Polevyye metody issledovaniya stroitel'nykh svoystv gruntov. Stroyizdat, Moscow.

GOST 19912-2001. Methods of field testing by static and dynamic sounding.

GOST 5686-94. Soil. Field pile test. BS 8004:1996 Foundations. British Standards Institution. BS EN 1997-1:2004 Eurocode EC7: Geotechnical Design – Part 1:

General Rules, 166. Zhusupbekov A.Zh., Alibekova N.T., Abilmazhenov T., Morev I.,

Zhagpаr A., Iwasaki Y., Mimura M. 2011. The modern approach to research of geotechnical properties of soils. Proceedings of the 14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, Hong Kong, China, 482-488.

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