geotechnical report and foundation recomendation

8/18/2019 Geotechnical Report and foundation recomendation

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GEOTECHNICAL SUB-SURFACE INVESTIGATION

AND FOUNDATION RECCOMENDATION REPORT

FOR

G+4 and G+7 CONDOMINIUM BUILDINGS



Addis Ababa Housing Construction office

Geotechnical Sub-Surface Investigations and Foundation Recommendations for G+4and G+7 condominium Building

BEST Consulting Engineers plc April 2014

TABLE OF CONTENTS

Page

1 INTRODUCTION ................................................................................................... 4

1.1 Background ........................................................................................................4

1.2 Scope of Work and Objective..............................................................................4

1.3 Location .............................................................................................................4

2 METHODOLOGY .................................................................................................. 6

2.1 Rotary Core Drilling ............................................................................................6

2.2 In-situ Tests ........................................................................................................6

2.3 Sampling ............................................................................................................6

2.3.1 Disturbed Soil Sampling .........................................................................6

2.3.2 Undisturbed Soil Sampling .....................................................................6

2.4 Laboratory Testing..............................................................................................7

2.5 Ground water monitoring...................................................................................8

3 GEOLOGIC AND SEISMIC SETTINGS OF THE AREA ............................................... 9

3.1 Regional and Site Geology ..................................................................................9

3.1.1 Regional Geology ...................................................................................9

3.1.2 Subsurface/Site Geology ...................................................................... 10

3.2 Regional Seismicity of the area ......................................................................... 10

3.2.1 Country seismicity overview................................................................. 11

3.2.2 Region seismicity overview .................................................................. 12

4 GEOTECHNICAL INVESTIGATION AND LABORATORY TESTING .......................... 13

4.1 Introduction ..................................................................................................... 13

4.2 Summary of the Geotechnical Investigation...................................................... 14

4.3 Geotechnical characterization of the subsurface material................................. 15

4.4 In situ Field Testing........................................................................................... 16

4.5 Sampling .......................................................................................................... 20

4.5.1 Disturbed Samples ............................................................................... 214.5.2 Undisturbed Samples........................................................................... 21

4.6 Laboratory Testing............................................................................................ 21

4.7 Ground water Level Measurement ................................................................... 26

4.8 Damage due to expansive soils ......................................................................... 26

4.8.1 Mitigation measures ............................................................................ 27

4.8.2 Treatment of Expansive Soils................................................................ 27

5 FOUNDATION ANALYSIS ................................................................................... 28

5.1 Introduction ..................................................................................................... 28

5.2 Isolated Foundation.......................................................................................... 28




Geotechnical Sub-Surface Investigations and Foundation Recommendations for G+4and G+7 condominium Building


5.2.1 Bearing Pressure Based on UCS............................................................ 28

5.2.2 Bearing Pressure Based on SPT N-Values for Isolated square Footing ... 30

5.3 Allowable Bearing capacity for Mat Foundation................................................ 37

5.4 Bearing Capacity using Settlement Criterion ..................................................... 38

6 CONCLUSION AND RECOMMENDATION ........................................................... 41

6.1 Subsurface geotechnical materials .................................................................. 41

6.2 Foundation seat and allowable bearing Capacity ............................................ 41

6.3 Material for backfill and compaction criteria .................................................. 43

6.4 Settlement consideration ................................................................................ 43

6.4.1 Seismic Consideration.......................................................................... 44

6.5 Considerations to Minimize Expansion Effect .................................................. 44

6.6 Other Consideration ........................................................................................ 45

REFERENCES ............................................................................................................ 46

LIST OF TABLES

Table 3-1: Seismic Hazard Rating (Gouin, 1976) ................................................................... 12

Table 4-1: Coordinate and Depth of Boreholes .................................................................... 13

Table 4-2: Summary of the Geotechnical Investigations Carried Out ................................... 14

Table 4-3: Distribution of the geotechnical layers in the boreholes...................................... 15

Table 4-4: Standard Penetration Test Results ...................................................................... 16

Table 4-5: Summary of UCS Test Result of undisturbed soil Samples.................................... 21

Table 4-6: Laboratory test results of disturbed soil samples................................................. 22

Table 4-7: Swelling pressure test result ............................................................................... 26

Table 4-8: Hydrometer analysis results on selected disturbed soil samples.......................... 26Table 5-1: Allowable Bearing Pressure Based on UCS Test Result of Soil Samples for Layer2.29

Table 5-2: Measured and adjusted SPT N values .................................................................. 31

Table 5-3: Allowable Bearing Pressures Based on SPT N-Value............................................. 36

Table 5-5-4: Allowable Bearing Pressures for Mat foundation Around G+7 Buildings ........... 38

Table 5-5: Bearing Pressure analysis using settlement criteria around BH-150..................... 40

Table 6-1: Summary of bearing capacity for Mat foundation ............................................... 42

APPENDICES

Appendix 1: Borehole Logs

Appendix 2: Laboratory Test Result

Appendix 3: Allowable Bearing Pressure Analysis Sheets




Geotechnical Sub-Surface Investigations and Foundation Recommendations for G+4 & G+7 Condominium Building


4

1 INTRODUCTION

1.1 Background

BEST Consulting Engineers private limited company has made a contract agreement with

Addis Ababa Housing Construction office to perform geotechnical investigations and provide

foundation recommendations for G+4 and G+7 Condominium buildings for Koye Feche

Project III Building site.

The building site is subdivided into different Parcels; accordingly twenty four boreholes (BH-

131 to BH-155) were sunk in Parcel 26 building area to a maximum depth of 10.0 meters and

15.0 meters below the natural ground for G+4 and G+7 buildings respectively.

The geotechnical investigations comprises of core drilling, in-situ tests such as Standard

Penetration Tests (SPT), monitoring of ground water, collection of representative samples,

and subsequent laboratory tests on representative samples to determine the engineering

properties of the sub-surface materials. Moreover, the coordinates of each borehole was

provided by the client and the ground elevation data were acquired using hand held GPS.

The field investigation was conducted from March 23 to March 24, 2013.

This report deals with the regional geology, site geology, methodology employed, laboratory

tests conducted to determine the engineering properties of the subsurface strata including

analyses and interpretation of test results. This report also encompasses foundation

recommendation including type of foundation, bearing layer, foundation depth, and

allowable bearing pressure for Parcel 26 building area.

1.2 Scope of Work and Objective

The scope of the geotechnical investigations include core drilling, in-situ tests, collection of

representative samples, subsequent laboratory testing, and ground water monitoring. The

prime objectives of the investigation are:-

a) To investigate the sub-surface geology of the proposed construction site and

identify the various soil horizons within the influence zone of foundation.

b) To carry out in-situ tests to determine the strength of the various soil horizons

within the influence zone of foundation.

c) To collect representative samples (disturbed and undisturbed) for subsequent

laboratory tests to determine the engineering properties.

d) To characterize the sub-surface materials into various geotechnical layers based

on combined parameters such as, visual description of soils/rocks, in-situ tests,and laboratory test results.

e) To provide safe and economic foundations, that is, type of foundation, bearing

layer, depth and width of foundation, and allowable bearing capacity.

1.3 Location

The project site is located in Addis Ababa, Akaki Kaliti Sub-City, around Koye Feche locality.

The project site is characterized by flat to rolling ground with an average elevation of 2205m

a.s.l.






5

Figure 1-1: Location map of the condominium site






6

2 METHODOLOGY

2.1 Rotary Core Drilling

Rotary core drilling was employed using wire line rig having the capacity to perform boring

operation to the required standard and quality in accordance with ASTM D 2113 – 93, ASTM

D 1452 – 80 (95), and BS 5930: 1981.Dry drilling method was employed in soil formations using inner lining single core barrels

fitted with appropriate size tungsten carbide bits at the bottom. This will enable the drilling

to achieve good quality core recovery. In rocky section, double core barrel fitted with

diamond bit was utilized. Water was pumped down to the bit through hollow drill rods to

cool the bit and flushing the cuttings up the borehole.

Equipments to conduct in-situ tests and sampling such as SPT apparatus including split

spoon sampler, Shelby Tubes, water pump, rods, casings, and a wide range of heavy-duty

tools were used during the drilling operations. An electric water meter was utilized in

monitoring the ground water level.

Materials recovered from the boreholes were placed in core boxes, labeled, logged andphotographed by digital camera according to their depths of recoveries. Core boxes were

stored in a safe place and carefully transported to BEST Consulting Engineers Plc central

laboratory. The core box samples will be kept for the next six (6) months and then will be

disposed if the client didn’t inform the company.

2.2 In-situ Tests

Standard Penetration Test (SPT) was conducted using a standard hammer, under an impact

of an automatic sliding hammer weighing 63.5kg falling freely from a height of 760mm in

accordance with ASTM D 1586 – 99 and BS 5930: 1981. The test was carried out starting

from 1.50m depth below natural ground level (NGL).

Blow counts for a total penetration depth of 450 mm from the bottom of a cleaned boreholewere recorded. Counts for the first 150 mm penetration were discarded since the ground is

considered to be disturbed during drilling activity prior to the test. SPT N-values for the last

300mm penetration are considered for computing the bearing capacity after applying the

necessary corrections.

2.3 Sampling

Disturbed and undisturbed soil samples were collected from the drilled bore holes at the

required depths and locations. Representative soil samples were collected as per ASTM and

BS standards, using the relevant samplers. Samples were recovered from split spoon sampler

after every SPT, Shelby-Tube and from core box.

2.3.1 Disturbed Soil Sampling

At the end of each SPT operation, the sampler tube is removed and disassembled to collect

representative disturbed sample for further laboratory tests. The disturbed samples were

properly sealed in plastic bags or small containers for NMC (Natural Moisture Content)

determination and other index tests. When the split spoon sample is in sufficient and not

found for a particular geotechnical layer, disturbed samples are also taken from core boxes.

2.3.2 Undisturbed Soil Sampling

Undisturbed Soil Samples are taken from cohesive materials encountered during drilling by

means of Shelby-Tube sampler. The samples are taken by applying static force and pressing






7

a Shelby Tube having an internal diameter of 80mm and length of 600mm. The top and

bottom of the Shelby tube samples were immediately wax sealed and covered with

polyethylene bags and labeled with necessary information for subsequent laboratory testing

to determine the engineering properties which are essential for providing the foundation

recommendations. All undisturbed samples were taken after dry boring and before SPT tests

to avoid disturbances.2.4 Laboratory Testing

BEST Consulting Engineers PLC (Private Limited Company) has a material testing laboratory

staffed with well-trained technician and engineers, in Addis Ababa. The laboratory is well

equipped by calibrated and certified ELE branded laboratory equipment to conduct various

index and engineering laboratory tests.

The following laboratory tests were conducted on different type of samples recovered from

boreholes in accordance with acceptable standards (such as, ASTM, AASHTO and BS

Standards).

Classification Tests

Classification tests are performed on collected representative samples for verification of the

field classification of the major soil types encountered during the investigation. A minor soil

type, if not critical, may be given a visual classification, instead of performing classification

test for reference. The classification tests performed for this project includes:

- Hydrometer and Sieve Analysis: - consist of determining the gradation of a

sample in accordance with AASHTO T-88.

- Atterberg Limit:- consist of the determination of the liquid limit, Plastic Limit

and Plasticity Index in accordance with AASHTO T89 and T90. If the soil is found

to be non-plastic, then the liquid limit shall not be performed, and the AASHTOgroup index shall be reported as zero.

Special Tests

These tests are performed on undisturbed soil samples, and/or split-spoon samples to

obtain additional information about the soils and their condition. In addition special tests

also include the analysis water samples. This information is used in analysis of conditions

and preparation of recommendations for design and construction. The special tests

performed for this project includes:

- Moisture content Test: determination of moisture content in accordance with

AASHTO T265, on representative samples of soil from each major stratum in each

boring.

- Unit Weight Determination: consist of the determination of the unit weight by

measurement of the length and diameter as performed in accordance with the

appropriate part of ASRM D-2937.

- Unconfined Compression Strength Test of soil: consist of performing the

unconfined compression test in accordance with ASTM D-2166. The test include

initial and final moisture content test, unit weight determination, visual description

of the soil, average strain at failure and average rate of strain of failure. This test






8

shall be performed on 3-inch undisturbed samples unless other types are specifically

approved in advance.

2.5 Ground water monitoring

The ground water level in each borehole was monitored before starting and after

completion of every day drilling activity. Presence of drilling water in boreholes, particularlyin cased ones, is often misleading with actual ground water level. Ground water level

measurements will only be reliable if measured for a reasonable period of times after

completion of the borehole.






9

3 GEOLOGIC AND SEISMIC SETTINGS OF THE AREA

3.1 Regional and Site Geology

3.1.1 Regional Geology

Addis Ababa city is situated in the western margin of the main Ethiopian Rift and representsa transitional zone between the Ethiopian Plateau and the rift with poorly defined

escarpment.

The geology of Addis Ababa area is represented by four volcanic units dominated in the

lower part by basaltic lava flows (Addis Ababa basalt), followed by a pyroclastic sequence,

mainly formed by ignimbrites (Addis Ababa Ignimbrite), followed by central composite

volcanoes (Central Volcanoes unit), and finally small spatter cones and lava flows (Akaki

unit).

Based on the Geologic Map of Addis Ababa City (Mulugeta H/Mariam et. al 2007), the

following volcanic formations are found in the project and surrounding area:-

1. Quaternary Olivine phyric Basalt (Qb): this unit is exposed in the northerncentral and southern part of Addis Ababa geologic map. It is grey in color on fresh

outcrop and becomes reddish brown up on weathering.

2. Quaternary Scoria (QSc): These scoria cones are found as either cones or simple

domes. Mostly, they are layered and sometimes contain grey Scoraceous basalt

bombs. This unit is mainly cut by basaltic dyke of different orientation.

3. Quaternary black cotton soil (Qs):

4. Chelekleka BASALT (Tb2): the oldest geological unit, found along the river course

(e.g. Akaki River and its tributaries). It is represented by layered BASALT

intercalated with scoria pyroclastic rock.

5. Tertiary sediments (Ts): Out crops are mainly observed at the banks of the river

and small creeks. It generally forms very gentle slope and lower topography. It is

overlain by the young Quaternary basalt and overlay the Repi basalt. The

maximum thickness is about 9 m which is around Akaki area.

6. Wechecha Yerer-Furi IGNIMBRITE (Ti3): locally covers the products of the

composite central volcanoes of Wechecha and Furi. The sequence is constituted

by different flow units, consisting of pale-green to pale-yellow welded and crystal

rich ignimbrites.

7. Lower ignimbrite and pyroclastic rock (Ti2): it is grey and black colored and

shows columnar jointing. The rock is medium to fine grained and is composed ofsanidine phenocrysts and fine grained ground mass. The top layer is very loose

massive ash deposit which is whitish in color.






10

Figure 3-1: Regional Geology of the area

3.1.2 Subsurface/Site Geology

The sub-surface geology of the proposed building sites is simple and fairly correlated in allthe boreholes sunk. Visual description of core samples was made following widely used and

practiced international procedures (such as, ASTM D 2488 – 93, BS 5930: 1981).

The top part of the project site is represented predominantly by soft to medium stiff, dark

grey, highly plastic CLAY with thickness ranging from 0.70m to 2.40m. This unit is underlain

in all the boreholes investigated by, dominantly, medium stiff to stiff, grayish brown, moist

and highly plastic Silty CLAY soil. The bottom part of the area is covered by light gray, slightly

weathered, dominantly closely to medium jointed, fine grained BASALT; this unit is

encountered from BH-151 to BH-154 only. Detailed descriptions of the sub-surface geology

encountered in all the boreholes are presented in the log sheets and cross sections attached

with this report (Appendix 1).

3.2 Regional Seismicity of the area

Stability and foundation of any civil engineering structures should be evaluated for seismic

stability. Information on the seismicity can be obtained from different sources that are

either from seismicity history of Ethiopia (seismicity zone map), regional location of the

country or localized or site specific study if it is needed. To do site specific earthquake hazard

analysis it demands detail study of faults by measuring slip rate, rupture length and depth of

energy release which are non-existence for this particular case.






11

3.2.1 Country seismicity overview

Earthquake is a common phenomenon that occurred daily in different magnitude and

frequency all over the world. In Ethiopia the afar depression and the Main Ethiopian Rift

(MER) which is part of the East African rift is where these earthquake epicenters were

aligned. Among them the 1960 Awasa earthquake (M=6.1), the 1961 Kara Kore earthquake,the 1969 Serdo earthquake (M=6.3), the 1983 Wendo Genet earthquake, the 1985 Langano

earthquake and the 1989 Dobi graben earthquake (M=6.5) were significant ones and some

of them were fatal. The current volcanic activities and the resulting geologic phenomena’s in

Afar and Main Ethiopian Rift (MER) are good manifestations for tectonically dynamic nature

of the zone.

Figure 4.1: Seismic zoning map of Ethiopia

This zone is also under earthquake magnitude (I100) of 7.4 to 6.5 on Richter scales and with

ground acceleration 10.0 to 4.6% g (Table 3-1). On both scales show that with thismagnitude seismic motion has minor damage.






12

Table 3-1: Seismic Hazard Rating (Gouin, 1976)

3.2.2 Region seismicity overview

From regional point of view the Global Seismic Hazard Assessment Program (GSHAP) which

was effective from 1992 to 1999 has produced digital data of Peak ground Acceleration

(PGA) and reports specific for several test areas including East African rift system. As per

GSHAP the project site is also located on the moderate seismic area of the country

characterized by a PAG of 0.8to 1.0m/s2 (Fig.4-2) over 50 years’ time.

Figure 3-2: Map that shows Peak ground Acceleration (After GSHAP, 1992-1999).

To generalize, the project site is located within the western rift margin of the country with

moderate seismic activity. Based on the Ethiopian Seismic Hazard Map (Gouin P 1976), the

area falls under Zone 2 corresponding moderate damage with VII MM intensity scale and

based on GSHAP it is located within a Peak Ground Acceleration (PGA) zone ranging from 0.8

to 1.0m/s2which is classified as seismically moderately vulnerable for potential damage.






13

4 GEOTECHNICAL INVESTIGATION AND LABORATORY TESTING

4.1 Introduction

The field geotechnical investigation had been performed with the help of core drilling,

sampling, insitu and laboratory testing. A total of twenty four (24) boreholes were drilled in

the building area and the co-ordinates and depths of the drilled boreholes are presented inTable 4-1.

Table 4-1: Coordinate and Depth of Boreholes

Sr.

No.BH-ID Easting Northing

Elevation

(m a.s.l)

Depth drilled

(m)

Boreholes at G+4 Building Sites

1 BH-143 480709.8739 985034.2030 2205 10

2 BH-144 480682.4774 985020.2660 2204 10

3 BH-145 480656.3469 985030.2021 2204 10

4 BH-146 480642.9868 985056.2095 2205 10

5 BH-147 480621.5830 985045.5805 2206 106 BH-148 480633.1591 985018.9585 2205 10

7 BH-149 480626.4520 984993.2795 2205 10

8 BH-150 480599.2936 984979.6320 2205 10

Boreholes at G+7 Building Sites

1 BH-131 480534.9863 985010.7899 2207 15

2 BH-132 480550.7011 985038.8251 2207 15

3 BH-133 480576.0159 985051.8397 2207 15

4 BH-134 480601.3875 985064.4364 2207 15

5 BH-135 480633.6238 985081.9554 2206 15

6 BH-136 480659.0453 985095.7982 2206 15

7 BH-137 480681.7767 985105.4902 2206 15

8 BH-138 480712.6727 985104.3926 2206 15

9 BH-139 480725.1287 985081.4795 2206 15

10 BH-140 480739.2475 985054.0753 2205 15

11 BH-141 480750.5019 985029.5674 2205 15

12 BH-142 480723.4073 985015.7022 2204 15

13 BH-151 480602.9246 984951.7569 2204 15

14 BH-152 480576.4438 984937.2897 2203 14

15 BH-153 480599.2936 984979.6320 2204 15

16 BH-154 480599.2936 984979.6320 2206 15






14

Figure 4-1: Location of the boreholes on Google image

From the above Google image, symbols with red circle represent borehole locations for G+7

buildings and the blue circles are borehole locations for G+4 buildings.

4.2 Summary of the Geotechnical Investigation

The detailed geotechnical investigations carried out including drilling, in-situ tests, and

laboratory tests were summarized and presented in Table 4-2.

Table 4-2: Summary of the Geotechnical Investigations Carried Out

Geotechnical investigations carried out Quantity

Inter borehole movement and setup of drilling equipment 24

Core drilling in ALL formation for G+4 80

Core drilling in ALL formation for G+7 239

Standard Penetration Tests (SPT) 186

Disturbed soil samples 149

Undisturbed samples 24

Ground water level measurement 24

Relative surface elevation of boreholes using hand held GPS 24

Core boxes and photographing of cores in core boxes 65

Laboratory Tests

Grain size analysis 149

Hydrometer analysis 12

Atterberg Limits 149

Free Swell 149






15

Geotechnical investigations carried out Quantity

Natural Moisture Content (NMC) 149

Unit weight 102

Specific gravity 149

Swelling pressure 4

Unconfined Compressive Strength of soil 24

4.3 Geotechnical characterization of the subsurface material

Based on visual description, in-situ and laboratory test results, the sub-surface geology is

sub-divided into various geotechnical layers. Accordingly, the geotechnical investigation

reveals the occurrence of three homogenous geotechnical layers.

Layer 1: Soft to Medium stiff, highly plastic CLAY

The top most part of the building site is covered by soft to medium stiff, dark grey,

highly plastic CLAY with a maximum thickness of 2.40 around BH-140 and BH-141

(Table 4-3).

Layer 2: Medium stiff to stiff, Silty CLAY

This layer is characterized by medium stiff to stiff, grayish brown, moist and highly

plastic Silty CLAY soil. It is encountered in all the boreholes underlying the top layer

1; the average field SPT N-values/300mm is 9.7 (Table 4-4).

Even if the soil is class is MH in USCS, after having discussion with the client and by

considering the nature of the soil type and the hydrometer analysis result, it has

been decided to set the soil in CH soil class.

Layer 3: Moderately to slightly weathered, fine grained BASALT

This layer is characterized by light gray, dominantly slightly weathered to fresh,

closely to medium spaced joints, fine grained BASALT. It is encountered in few of the

boreholes drilled (Table 4-3).

Table 4-3: Distribution of the geotechnical layers in the boreholes

BH-IDDepth of occurrence (m)

Layer 1 Layer 2 Layer 3

Around G+4 Buildings

BH-143 0.00 – 2.00 2.00 – 10.00 -

BH-144 0.00 – 2.00 2.00 – 10.00 -

BH-145 0.00 – 1.50 1.50 – 10.00 -

BH-146 0.00 – 1.50 1.50 – 10.00 -

BH-147 0.00 – 1.50 1.50 – 10.00 -

BH-148 0.00 – 1.50 1.50 – 10.00 -

BH-149 0.00 – 1.50 1.50 – 10.00 -

BH-150 0.00 – 2.00 1.30 – 10.00 -


BH-131 0.00 – 1.50 1.50 – 15.00 -






16

BH-IDDepth of occurrence (m)

Layer 1 Layer 2 Layer 3

BH-132 0.00 – 1.50 1.50 – 15.00 -

BH-133 0.00 – 1.50 1.50 – 15.00 -

BH-134 0.00 – 1.50 1.50 – 15.00 -

BH-135 0.00 – 0.70 0.70 – 15.00 -

BH-136 0.00 – 1.40 1.40 – 15.00 -

BH-137 0.00 – 1.50 1.50 – 15.00 -

BH-138 0.00 – 1.50 1.50 – 15.00 -

BH-139 0.00 – 2.20 2.20 – 15.00 -

BH-140 0.00 – 2.40 2.40 – 15.00 -

BH-141 0.00 – 2.40 2.40 – 15.00 -

BH-142 0.00 – 2.30 2.30 – 15.00 -

BH-151 0.00 – 1.50 1.50 – 13.45 13.45-15.00

BH-152 0.00 – 1.00 1.00 – 11.00 11.00-14.00

BH-153 0.00 – 1.50 1.50 – 11.80 11.80-15.00

BH-154 0.00 – 1.50 1.50-12.80 12.80-15.00

4.4 In situ Field Testing

The only insitu test conducted in the drilled boreholes is Standard Penetration Test (SPT)

using a standard hammer, under an impact of an automatic sliding hammer. The test was

carried out starting from 1.5m depth below natural ground level (NGL). Accordingly, a total

of one hundred eighty six (186) SPT tests were carried out. Summary of the SPT test results

are given in Table 5-4 below.

Table 4-4: Standard Penetration Test Results

Sr.

No BH-ID Depth (m)Material Description

Measured

SPT values

SPT N-

values/

300mm


1 BH-143

1.55-2.00 CLAY 2/1/2 3

3.10-3.55

Silty CLAY

2/2/3 5

4.55-5.00 3/4/5 9

6.00-6.45 4/5/6 11

7.55-8.00 4/6/9 15

9.00-9.45 5/7/8 15

2 BH-144

1.50-1.95 CLAY 2/1/3 4

3.00-3.45

Silty CLAY

1/2/3 5

4.50-4.95 2/2/3 5

6.00-6.45 3/4/4 8

7.50-7.95 3/4/5 9

9.00-9.45 4/4/5 9

3 BH-145

1.55-2.00

Silty CLAY

2/2/3 5

3.10-3.55 1/2/4 6

4.55-5.00 2/3/5 8

6.00-6.45 3/4/6 10






17

Sr.


Measured

SPT values

SPT N-

values/

300mm

7.50-7.95 3/4/8 12

9.00-9.45 3/5/8 13

4BH-146

1.55-2.00

Silty CLAY

2/2/2 4

3.10-3.55 2/2/3 5

4.55-5.00 2/3/4 7

6.00-6.45 3/3/5 8

7.55-8.00 3/4/5 9

9.00-9.45 4/5/6 11

5 BH-147

1.55-2.00

Silty CLAY

1/2/3 5

3.10-3.55 2/2/2 4

4.55-5.00 3/4/6 10

6.00-6.45 3/4/3 7

7.55-8.00 3/5/7 129.00-9.45 4/5/8 13

6 BH-148

1.55-2.00

Silty CLAY

2/1/3 4

3.10-3.55 2/2/4 6

4.55-5.00 2/4/6 10

6.00-6.45 3/4/5 9

7.55-8.00 3/3/4 7

9.00-9.45 3/3/5 8

7 BH-149

1.55-2.00

Silty CLAY

1/2/2 4

3.10-3.55 2/2/4 6

4.55-5.00 3/5/6 11

6.00-6.45 4/5/7 12

7.55-8.00 4/6/8 14

9.00-9.45 5/7/8 15

8BH-150

1.55-2.00 CLAY 3/2/11 13

3.10-3.55

Silty CLAY

2/3/5 8

4.55-5.00 3/5/7 12

6.00-6.45 5/7/10 17

7.55-8.00 6/8/10 18

9.00-9.45 6/7/11 18


1 BH-131

1.55 – 2.00

Silty CLAY

1/1/2 33.00 - 3.45 2/3/4 7

4.50 – 4.95 2/3/6 9

6.00 - 6.45 2/4/6 10

7.50 – 7.95 3/5/6 11

9.00 - 9.45 3/4/5 9

10.5 - 10.95 3/4/6 10

12.00 - 12.45 3/5/6 11

13.5 - 13.95 4/5/5 10

2 BH-1321.50-1.95

Silty CLAY 1/2/3 5

3.10-3.552/3/3

6






18

Sr.


Measured

SPT values

SPT N-

values/

300mm

4.50-4.95 2/2/4 6

6.00-6.45 2/3/3 6

7.55-8.00 Clayey Silty SAND 3/3/4 7

9.00-9.45

Silty CLAY

2/4/4 8

10.50-10.95 2/3/6 9

12.00-12.45 3/3/6 9

13.50-13.95 3/4/7 11

3 BH-133

1.55-2.00

Silty CLAY

2/1/2 3

3.00-3.45 2/3/4 7

4.50-4.95 2/2/4 6

6.00-6.45 2/2/3 5

7.50-7.95 2/3/4 7

9.00-9.45 2/3/5 810.50-10.95 3/3/6 9

12.00-12.45 3/4/6 10

13.50-13.55 4/4/7 11

4 BH-134

1.55-2.00

Silty CLAY

1/2/3 5

3.00-3.45 2/3/4 7

4.50-4.95 2/3/6 9

6.00-6.45 6/5/10 15

7.55-7.95 3/3/5 8

9.00-9.45 3/3/4 7

10.55-11.00 2/3/5 8

12.00-12.45 3/3/5 8

13.55-14.00 3/4/6 10

5 BH-135

1.50-1.95

Silty CLAY

1/2/2 4

3.00-3.45 2/2/3 5

4.50-4.95 3/3/3 6

6.00-6.45 3/3/5 8

7.55-7.95 3/4/6 10

9.00-9.45 3/6/7 13

10.50-10.95 2/3/5 8

12.00-12.45 3/4/6 10

13.50-13.95 4/6/6 12

6 BH-136

1.55-2.00

Silty CLAY

2/2/2 4

3.00-3.45 2/3/5 8

4.50-4.95 3/4/5 9

6.00-6.45 4/5/5 10

7.55-7.95 4/4/6 10

9.00-9.45 3/5/6 11

10.50-10.95 3/5/7 12

12.00-12.45 4/5/6 11

13.50-13.95 4/6/7 13

7 BH-137 1.50-1.95 Silty CLAY 1/1/2

3






19

Sr.


Measured

SPT values

SPT N-

values/

300mm

3.00-3.45 2/3/3 6

4.50-4.95 2/2/5 7

6.00-6.45 2/4/5 9

7.50-7.95 3/3/5 8

9.00-9.45 3/5/5 10

10.50-10.95 2/5/7 12

12.00-12.45 3/6/6 12

13.50-13.95 4/5/6 11

8 BH-138

1.50-1.95

Silty CLAY

1/1/2 3

3.00-3.45 2/3/4 7

4.50-4.95 2/4/7 11

6.00-6.45 2/4/7 11

7.50-7.95 3/4/6 109.00-9.45 3/3/3 6

10.55-11.00 3/4/6 10

12.00-12.45 4/5/6 11

13.50-13.95 5/6/7 13

9 BH-139

1.50-1.95 CLAY 2/2/2 4

3.00-3.45

Silty CLAY

2/2/4 6

4.50-4.95 2/3/4 7

6.00-6.45 2/4/8 12

7.50-7.95 2/3/4 7

9.00-9.45 3/4/6 10

10.50-10.95 3/5/6 11

12.00-12.45 4/5/6 11

13.50-13.95 3/6/7 13

10 BH-140

1.50-1.95 CLAY 1/2/3 5

3.00-3.45

Silty CLAY

2/2/3 5

4.50-4.95 2/3/5 8

6.00-6.45 3/4/5 9

7.50-7.95 3/4/6 10

9.00-9.45 2/4/6 10

10.50-10.95 3/5/6 11

12.00-12.45 Silty CLAY 4/4/6 1013.50-13.95 4/5/7 12

11 BH-141

1.50-1.95 CLAY 1/1/2 3

3.00-3.45

Silty CLAY

2/3/3 6

4.50-4.95 3/3/4 7

6.00-6.45 2/4/6 10

7.50-7.95 3/5/5 10

9.00-9.45 3/5/6 11

10.50-10.95 4/4/5 9

12.00-12.45 3/5/6 11

13.50-13.954/6/6

12






20

Sr.


Measured

SPT values

SPT N-

values/

300mm

12 BH-142

1.55-2.00 CLAY 1/2/2 4

3.00-3.45

Silty CLAY

2/3/3 6

4.50-4.95 2/3/5 8

6.00-6.45 3/4/6 10

7.50-7.95 3/3/5 8

9.00-9.45 3/5/6 11

10.50-10.95 3/4/5 9

12.00-12.45 4/4/6 10

13.50-13.95 4/5/6 11

13 BH-151

1.55-2.00

Silty CLAY

1/2/3 5

3.10-3.55 2/4/5 9

4.50-4.95 3/5/6 11

6.00-6.45 3/6/8 147.55-8.00 3/7/9 16

9.00-9.45 5/8/10 18

10.55-11.00 6/9/10 19

12.00-12.45 6/8/11 19

14 BH-152

1.55-2.00

Silty CLAY

2/2/3 5

3.10-3.55 3/3/5 8

4.55-5.00 4/5/6 11

6.00-6.45 3/5/7 12

7.55-8.00 4/7/9 16

9.00-9.45 6/8/9 17

10.55-11.00 R 50

15 BH-153

1.55-2.00

Silty CLAY

1/2/3 5

3.10-3.55 3/5/6 11

4.55-5.00 4/5/6 11

6.00-6.45 4/6/6 12

7.55-8.00 2/3/4 7

9.00-9.45 3/3/5 8

10.55-11.00 4/7/9 16

16 BH-154

1.50-1.95

Silty CLAY

2/3/4 7

3.10-3.55 2/3/5 8

4.50-4.95 3/4/6 106.00-6.45 4/5/9 14

7.50-7.95 5/6/9 15

9.00-9.45 7/8/10 18

10.55-11.00 4/5/6 11

12.00-12.45 3/6/8 14

4.5 Sampling

A total of one hundred seventy three (173) representative samples were collected from the

drilled boreholes for subsequent laboratory tests.






21

4.5.1 Disturbed Samples

A total of one hundred forty nine (149) representative disturbed soil samples were collected

from split spoon sampler and core box. At the end of each SPT operation, the sampler tube

is removed and disassembled to collect representative disturbed sample for further

laboratory tests.

4.5.2 Undisturbed Samples

Twenty four undisturbed samples were collected by applying static force and pressing a

Shelby Tube having an internal diameter of 80mm and length of 600mm (in accordance with

ASTM D 1587 – 94 and BS 5930: 1981). The top and bottom of the Shelby Tube samples

were immediately wax sealed and covered with polyethylene bags and labeled with all

relevant information for subsequent laboratory testing to determine their geotechnical

properties. To avoid disturbances, all undisturbed samples were taken after dry boring and

before SPT.

4.6 Laboratory Testing

Representative disturbed and undisturbed soil samples collected from the boreholes were

brought to BEST Consulting Engineers Plc Central Laboratory and subjected to different kind

of quantitative and qualitative tests.

The laboratory testing on the disturbed soil samples include Atterberg Limits, sieve analyses,

hydrometer analysis, moisture content, specific gravity and free swell tests. Undisturbed

samples collected were also subjected to Unconfined Compressive Strength (UCS) tests,

Swelling pressure and Bulk density measurements.

Summary of all the laboratory test results are presented in Table 4-5 to Table 4-8 and the

details in Appendix 2.

Table 4-5: Summary of UCS Test Result of undisturbed soil Samples

BH ID. Depth (m)

Bulk Unit

Weight

(KN/m3)

Dry Unit

Weight

(KN/m3)

Moisture

Content (%)

UCS

(KPa)

Cu

(KPa)


BH - 143 2.50-3.10 17.19 11.66 47.39 51.11 25.56

BH - 144 2.50-3.00 17.41 11.31 53.90 53.80 26.90

BH - 145 2.50-3.10 16.41 10.35 58.51 58.98 29.49

BH - 146 2.50-3.10 16.08 10.84 48.43 42.12 21.06

BH - 147 2.50-3.10 15.95 10.45 52.68 55.30 27.65

BH - 148 2.50-3.10 16.77 11.23 49.30 49.44 24.72

BH - 149 2.50-3.10 16.12 10.63 51.66 64.50 32.25

BH - 150 2.50-3.10 17.50 11.44 52.90 61.87 30.94

Around G+7 Building

BH - 131 2.50-3.00 16.53 10.85 52.44 57.12 28.56

BH - 132 2.50-3.00 17.49 12.20 43.33 96.95 48.48

BH - 133 2.50-3.10 17.76 12.20 45.62 45.19 22.60

BH - 134 2.50-3.10 16.02 11.02 45.27 83.40 41.70

BH - 135 2.50-3.00 17.50 11.61 50.75 56.27 28.14

BH - 136 2.50-3.00 17.09 12.16 40.56 62.86 31.43

BH - 137 2.50-3.00 17.22 11.50 49.77 58.30 29.15

BH - 138 2.50-3.00 16.69 10.69 56.08 70.16 35.08






22

Table 4-6: Laboratory test results of disturbed soil samples

SrNo

BH-ID Depth (m) NMC GsWet Sieve Analysis

(AASHTO T27)

AtterbergLimit

(AASHTOT89&90) USCS

FreeSwell(%)

2.mm0.425mm

0.075mm

LL PL PI


1 BH-143 1.50-2.10 52.17 2.62 99.7 99.0 98.6 93 51 42 CH 200

2 BH-143 3.10-3.70 45.90 2.63 99.7 99.6 99.0 91 51 40 CH 190

3 BH-143 4.50-5.10 51.35 2.60 98.3 97.3 95.8 89 50 39 CH 150

4 BH-143 9.00-9.60 40.77 2.57 96.3 95.5 94.6 98 52 46 CH 180

5 BH-144 1.50-2.10 42.92 2.63 77.2 75.3 74.3 81 48 33 CH 160

6 BH-144 3.00-3.60 47.19 2.61 99.5 98.8 98.3 84 50 34 CH 170

7 BH-144 4.50-5.10 35.92 2.58 99.7 99.1 97.5 86 50 36 CH 150

8 BH-144 9.00-9.60 43.81 2.60 84.7 83.7 83.2 95 51 44 CH 190

9 BH-145 1.50-2.10 53.61 2.63 95.4 95.1 94.7 93 50 43 CH 180

10 BH-145 3.10-3.70 51.15 2.60 97.4 97.3 97.1 112 58 54 CH 200

11 BH-145 4.50-5.10 49.89 2.58 99.9 99.7 98.9 71 49 22 CH 130

12 BH-145 6.00-6.60 43.96 2.61 97.5 97.0 96.5 89 51 38 CH 150

13 BH-145 9.00-9.60 41.96 2.62 99.0 98.7 98.1 93 52 41 CH 190

14 BH-146 3.10-3.70 50.00 2.6 93.6 92.9 91.5 97 52 45 CH 180

15 BH-146 4.50-5.10 50.78 2.58 99.8 99.7 99.3 105 55 50 CH 160

16 BH-146 6.00-6.60 43.18 2.60 97.0 96.0 95.4 87 48 39 CH 190

17 BH-146 9.00-9.60 40.12 2.57 93.2 90.7 88.7 71 38 33 CH 140

18 BH-147 1.50-2.10 44.84 2.60 92.5 90.2 89.3 91 47 44 CH 190

19 BH-147 3.10-3.70 49.82 2.62 96.7 95.0 94.0 102 44 58 CH 180

20 BH-147 4.50-5.10 44.14 2.59 97.0 95.8 94.3 93 51 42 CH 140

21 BH-147 6.00-6.60 42.49 2.58 95.6 94.7 93.9 84 47 37 CH 170

22 BH-147 9.00-9.60 40.66 2.61 96.2 95.0 93.6 78 47 31 CH 150

23 BH-148 3.10-3.70 46.22 2.60 98.8 98.4 98.1 90 56 34 CH 190

24 BH-148 4.50-5.10 52.45 2.58 98.0 96.7 95.7 72 52 20 CH 140

25 BH-148 6.00-6.60 42.54 2.63 95.2 93.9 92.9 81 43 38 CH 160

26 BH-148 9.00-9.60 44.98 2.61 99.2 98.7 97.9 98 53 45 CH 170

27 BH-149 1.50-2.10 31.15 2.64 94.8 93.9 93.4 86 47 39 CH 190

28 BH-149 3.10-3.70 25.90 2.58 99.3 97.8 96.8 85 49 36 CH 140

29 BH-149 4.50-5.10 31.62 2.62 99.6 99.0 98.4 82 45 37 CH 150

30 BH-149 9.00-9.60 46.62 2.60 99.8 99.3 97.6 90 49 41 CH 180

BH - 139 2.50-3.00 18.66 13.09 42.55 48.98 24.49

BH - 140 2.50-3.00 18.14 12.78 41.92 94.37 47.19

BH - 141 2.50-3.00 16.63 10.73 54.94 92.98 46.49

BH - 142 2.50-3.00 16.85 12.07 39.57 102.40 51.20

BH - 153 2.50-3.10 16.63 10.96 51.68 79.11 39.56

BH - 154 2.50-3.10 17.02 11.80 44.25 62.02 31.01

BH - 151 2.50-3.10 16.55 10.45 58.27 75.36 37.68

BH - 152 2.50-3.10 17.61 10.87 62.03 80.04 40.02






23

SrNo


(AASHTO T27)

AtterbergLimit

(AASHTOT89&90) USCS

FreeSwell(%)

2.mm0.425mm

0.075mm

LL PL PI

31 BH-150 3.10-3.70 45.60 2.61 98.7 98.3 98.0 102 66 36 CH 190

32 BH-150 4.50-5.10 46.36 2.64 99.5 99.3 98.6 99 51 48 CH 170

33 BH-150 6.00-6.60 29.57 2.59 96.5 95.7 95.1 91 50 41 CH 150

34 BH-150 9.00-9.60 41.69 2.61 96.8 96.2 95.1 86 45 41 CH 140


35 BH-131 1.50-2.10 41.77 2.62 90.7 88.0 87.5 83 46 37 CH 130

36 BH-131 3.00-3.60 43.47 2.59 98.7 98.4 97.9 89 48 41 CH 150

37 BH-131 4.50-5.10 39.50 2.61 98.66 98.3 97.0 84 49 35 CH 160

38 BH-131 6.00-6.60 48.74 2.60 98.4 97.8 96.3 72 44 28 CH 140

39 BH-131 7.50-8.10 43.19 2.59 97.5 97.3 96.7 88 47 41 CH 17040 BH-131 9.00-9.60 38.16 2.58 99.7 99.4 99.0 90 52 38 CH 150

41 BH-131 10.5-11.10 37.60 2.59 99.5 98.6 97.9 87 50 37 CH 160

42 BH-131 12.0-12.60 22.22 2.61 99.3 99.0 97.9 87 46 41 CH 180

43 BH-131 13.5-14.10 39.64 2.57 98.8 97.9 96.8 72 45 27 CH 120

44 BH-132 1.50-2.10 43.61 2.58 99.6 99.5 99.0 94 50 44 CH 160

45 BH-132 3.00-3.60 24.06 2.61 96.6 95.9 95.4 106 57 49 CH 150

46 BH-132 4.50-5.10 40.97 2.63 99.5 98.9 98.0 105 55 50 CH 180

47 BH-132 6.00-6.60 41.47 2.61 99.5 99.3 98.5 96 51 45 CH 140

48 BH-132 7.50-8.10 33.99 2.58 28.3 20.0 11.6 36 26 10 SM 30

49 BH-132 9.00-9.60 33.49 2.62 90.6 89.7 88.4 71 41 30 CH 12050 BH-132 10.5-11.10 31.67 2.58 99.5 98.9 98.5 101 52 49 CH 190

51 BH-132 12.0-12.60 35.58 2.57 99.4 98.7 97.9 84 47 37 CH 130

52 BH-132 13.5-14.10 20.48 2.56 99.5 98.9 98.0 94 50 44 CH 190

53 BH-133 1.50-2.10 41.33 2.61 91.4 90.4 89.9 104 54 50 CH 180

54 BH-133 3.10-3.70 45.70 2.64 99.6 98.9 98.0 95 50 45 CH 160

55 BH-133 4.50-5.10 35.93 2.60 85.8 84.8 84.2 93 49 44 CH 200

56 BH-133 6.00-6.60 39.47 2.57 93.9 92.4 91.4 100 55 45 CH 180

57 BH-133 7.50-8.10 43.28 2.59 84.8 83.5 82.3 71 43 28 CH 140

58 BH-133 9.00-9.60 35.97 2.60 99.8 99.3 98.8 80 49 31 CH 160

59 BH-133 10.5-11.10 27.46 2.57 94.6 94.0 92.7 96 51 45 CH 13060 BH-133 12.0-12.60 29.17 2.59 98.5 97.9 96.3 98 52 46 CH 150

61 BH-133 13.5-14.10 41.92 2.57 99.6 98.9 93.4 72 39 33 CH 120

62 BH-134 1.50-2.10 48.45 2.60 81.4 79.6 78.8 90 49 41 CH 180

63 BH-134 3.10-3.70 37.59 2.61 99.6 99.2 98.6 95 50 45 CH 160

64 BH-134 4.50-5.10 41.43 2.58 99.6 98.9 98.2 94 51 43 CH 150

65 BH-134 6.00-6.60 38.26 2.62 93.6 93.0 91.5 89 48 41 CH 160

66 BH-134 7.50-8.10 40.10 2.60 98.5 97.9 97.0 101 53 48 CH 180

67 BH-134 9.00-9.60 35.08 2.58 99.9 99.7 98.4 87 48 39 CH 150

68 BH-134 10.5-11.10 39.23 2.59 99.5 98.9 98.0 98 50 48 CH 170

69 BH-134 12.0-12.60 35.66 2.57 99.7 99.2 98.8 91 50 41 CH 150






24

SrNo


(AASHTO T27)

AtterbergLimit

(AASHTOT89&90) USCS

FreeSwell(%)

2.mm0.425mm

0.075mm

LL PL PI

70 BH-134 13.5-14.10 31.49 2.59 98.3 97.9 97.0 93 48 45 CH 130

71 BH-135 1.50-2.10 38.57 2.63 95.5 94.8 93.7 80 50 30 CH 190

72 BH-135 3.00-3.60 43.78 2.61 99.6 99.0 98.4 98 55 43 CH 160

73 BH-135 4.50-5.10 43.29 2.59 99.4 98.6 97.8 89 49 40 CH 190

74 BH-135 6.00-6.60 34.98 2.61 99.4 98.6 98.0 93 52 41 CH 170

75 BH-135 7.50-8.10 30.37 2.60 99.5 98.4 97.6 81 44 37 CH 180

76 BH-135 9.00-9.60 38.52 2.57 99.8 99.6 98.7 79 44 35 CH 140

77 BH-135 10.5-11.10 41.93 2.59 95.6 93.9 93.1 82 48 34 CH 170

78 BH-135 12.0-12.60 38.75 2.58 99.7 99.2 98.3 79 43 36 CH 150

79 BH-135 13.5-14.10 31.89 2.57 99.5 98.9 98.1 99 53 46 CH 130

80 BH-136 1.50-2.10 40.18 2.62 93.8 93.2 92.3 64 38 26 CH 160

81 BH-136 3.00-3.60 38.46 2.63 99.5 98.2 96.9 83 53 30 CH 170

82 BH-136 4.50-5.10 41.77 2.60 99.5 98.8 98.2 90 49 41 CH 130

83 BH-136 6.00-6.60 43.69 2.58 92.6 90.9 90.0 83 47 36 CH 150

84 BH-136 7.50-8.10 36.84 2.56 97.8 97.3 96.5 74 46 28 CH 170

85 BH-136 9.00-9.60 30.26 2.59 92.1 91.4 90.3 78 40 38 CH 190

86 BH-136 10.5-11.10 38.24 2.61 99.4 98.5 97.7 82 47 35 CH 180

87 BH-136 12.0-12.60 36.18 2.58 99.4 99.1 98.4 81 50 31 CH 150

88 BH-136 13.5-14.10 39.84 2.60 99.7 99.5 98.8 80 50 30 CH 130

89 BH-137 1.50-2.10 30.13 2.64 95.1 94.1 93.2 94 49 45 CH 150

90 BH-137 3.00-3.60 56.06 2.61 94.0 93.6 92.5 92 48 44 CH 180

91 BH-137 4.50-5.10 47.68 2.59 99.4 98.4 96.0 82 43 39 CH 140

92 BH-137 7.50-8.10 42.19 2.61 98.7 97.8 95.7 85 47 38 CH 180

93 BH-137 10.5-11.10 43.66 2.57 98.4 98.0 97.5 104 54 50 CH 160

94 BH-137 13.5-14.10 44.45 2.62 99.8 99.3 97.2 85 50 35 CH 100

95 BH-138 1.50-2.10 48.23 2.63 94.6 93.6 93.1 89 50 39 CH 170

96 BH-138 3.00-3.60 38.23 2.60 99.5 98.7 98.1 84 47 37 CH 160

97 BH-138 4.50-5.10 42.47 2.62 100.0 99.9 99.2 92 54 38 CH 160

98 BH-138 7.50-8.10 46.72 2.60 99.5 98.6 97.6 84 49 35 CH 180

99 BH-138 10.5-11.10 38.27 2.58 88.0 87.0 86.4 77 45 32 CH 140

100 BH-138 13.5-14.10 40.16 2.57 100.0 99.8 99.1 85 49 36 CH 100

101 BH-139 1.50-2.10 47.18 2.64 91.4 87.0 84.4 75 39 36 CH 160

102 BH-139 3.00-3.60 50.47 2.61 91.8 91.4 91.3 96 49 47 CH 160

103 BH-139 4.50-5.10 35.14 2.62 94.9 93.8 93.1 97 50 47 CH 170

104 BH-139 7.50-8.10 51.97 2.58 98.0 97.5 96.4 71 41 30 CH 40

105 BH-139 10.5-11.10 44.65 2.62 98.4 97.8 96.1 93 43 50 CH 150

106 BH-139 13.5-14.10 37.64 2.64 99.6 98.6 97.4 91 43 48 CH 190

107 BH-140 1.50-2.10 48.24 2.64 89.6 88.7 87.7 84 46 38 CH 160

108 BH-140 3.00-3.60 49.38 2.60 95.6 94.2 92.6 82 43 39 CH 180

109 BH-140 4.50-5.10 46.86 2.58 91.7 90.9 90.4 90 48 42 CH 160






25

SrNo


(AASHTO T27)

AtterbergLimit

(AASHTOT89&90) USCS

FreeSwell(%)

2.mm0.425mm

0.075mm

LL PL PI

110 BH-140 7.50-8.10 40.79 2.61 99.5 99.3 98.6 101 52 49 CH 150

111 BH-140 10.5-11.10 40.98 2.58 98.8 98.4 97.6 88 46 42 CH 170

112 BH-140 13.5-14.10 36.91 2.60 92.6 90.5 88.5 75 40 35 CH 140

113 BH-141 1.50-2.10 47.27 2.63 95.0 93.5 91.6 91 48 43 CH 150

114 BH-141 3.00-3.60 34.18 2.60 88.2 87.6 87.4 107 57 50 CH 200

115 BH-141 4.50-5.10 34.12 2.61 99.6 98.7 97.9 85 46 39 CH 150

116 BH-141 7.50-8.10 45.62 2.58 97.6 96.8 95.7 83 48 35 CH 180

117 BH-141 10.5-11.10 35.33 2.61 93.1 92.4 91.1 85 43 42 CH 170

118 BH-141 13.5-14.10 26.62 2.64 96.6 94.6 91.8 74 39 35 CH 140

119 BH-142 1.50-2.10 34.71 2.64 99.5 98.8 98.2 95 50 45 CH 130

120 BH-142 3.00-3.60 42.74 2.59 90.5 89.2 88.4 92 49 43 CH 160

121 BH-142 4.50-5.10 42.24 2.58 99.6 98.9 98.2 99 53 46 CH 190

122 BH-142 7.50-8.10 37.82 2.60 99.6 98.9 98.4 90 54 36 CH 180

123 BH-142 10.5-11.10 35.21 2.61 99.8 99.0 98.2 78 41 37 CH 150

124 BH-142 13.5-14.10 39.96 2.58 98.6 97.2 95.7 88 49 39 CH 170

125 BH-151 1.50-2.10 42.70 2.64 99.7 99.1 98.5 96 51 45 CH 170

126 BH-151 3.10-3.70 55.91 2.60 99.6 99.0 98.4 87 47 40 CH 150

127 BH-151 4.50-5.10 42.15 2.62 99.7 99.5 98.8 98 55 43 CH 190

128 BH-151 7.50-8.10 44.44 2.60 98.6 98.2 97.8 90 54 36 CH 140

129 BH-151 12.0-12.60 41.49 2.60 93.9 92.6 91.6 82 47 35 CH 130

130 BH-152 1.50-2.10 50.26 2.62 98.9 98.4 97.7 93 53 40 CH 170

131 BH-152 3.10-3.70 53.54 2.63 99.6 98.9 98.1 99 52 47 CH 190

132 BH-152 4.50-5.10 42.25 2.61 93.3 91.5 90.9 95 42 53 CH 160

133 BH-152 7.50-8.10 42.31 2.58 99.0 98.5 97.9 90 49 41 CH 180

134 BH-152 10.4-11.00 44.89 2.60 72.8 69.2 67.6 59 30 29 CH 120

135 BH-153 1.50-2.10 47.90 2.63 99.3 99.1 98.1 103 54 49 CH 190

136 BH-153 3.10-3.70 49.42 2.60 99.8 99.3 97.7 83 46 37 CH 130

137 BH-153 4.50-5.10 35.56 2.58 99.5 98.9 98.3 92 49 43 CH 160

138 BH-153 6.00-6.60 37.92 2.60 94.3 94.2 93.9 97 51 46 CH 190

139 BH-153 7.50-8.10 31.72 2.59 99.5 98.7 97.8 90 53 37 CH 180

140 BH-153 9.00-9.60 36.46 2.61 99.2 98.6 98.0 99 51 48 CH 200

141 BH-153 10.5-11.10 35.35 2.61 99.4 98.9 98.2 91 51 40 CH 140

142 BH-154 1.50-2.10 36.32 2.63 95.4 94.8 94.1 96 39 57 CH 160

143 BH-154 3.10-3.70 34.56 2.64 98.6 98.4 97.5 93 53 40 CH 130

144 BH-154 4.50-5.10 35.14 2.59 99.4 98.6 97.7 88 52 36 CH 180

145 BH-154 6.00-6.60 38.90 2.61 99.6 98.8 97.8 92 50 42 CH 150

146 BH-154 7.50-8.10 34.17 2.59 99.2 99.0 98.1 75 46 29 CH 120

147 BH-154 9.00-9.60 25.72 2.57 99.5 98.4 97.0 82 45 37 CH 190

148 BH-154 10.5-11.10 27.10 2.62 99.1 98.7 97.5 98 51 47 CH 170

149 BH-154 12.0-12.60 36.19 2.60 98.2 97.8 96.5 70 38 32 CH 160






26

Table 4-7: Swelling pressure test result

Sr. No BH-ID Depth, m NMC Swelling Pressure, Kpa

1 BH - 131 2.50-3.10 52.44 37.0

2 BH - 135 2.50-3.10 50.75 42.2

3 BH - 142 2.50-3.00 39.57 45.7

4 BH - 146 2.50-3.10 48.43 39.5

Table 4-8:

Hydrometer analysis results on selected disturbed soil samples

Sr No BH-ID Depth (m)

HYDROMETER TYPE 152H

Sand%

(2.00 – 0.075mm)

Silt%

(0.075 – 0.002mm)

Clay%

(< 0.002)

1 BH-131 3.00-3.60 3.1 34.9 62.0

2 BH-132 3.00-3.60 5.4 31.6 63.0

3 BH-136 3.00-3.60 4.0 39.0 57.0

4 BH-137 3.00-3.60 7.9 28.1 64.05 BH-139 3.00-3.60 10.2 30.8 59.0

6 BH-141 3.00-3.60 14.0 30.0 56.0

7 BH-143 4.50-5.10 4.8 31.2 64.0

8 BH-145 3.10-3.70 4.0 30.0 66.0

9 BH-148 3.10-3.70 2.9 31.1 66.0

10 BH-149 4.40-5.00 2.4 29.6 68.0

11 BH-151 4.50-5.10 2.5 29.5 68.0

12 BH-154 3.10-3.70 3.2 28.8 68.0

4.7 Ground water Level Measurement

When encountered, ground water level is measured every day before and after 24 hour

from completion of drilling activity. There was no groundwater occurrence in all the drilled

boreholes up to the target depth.

4.8 Damage due to expansive soils

Potentially expansive soils were identified in the building site during the geotechnical

investigation. Expansive soils are prone to change in volume because of the presence or

absence of moisture, which can cause the soils to shrink or swell, resulting in damage to

structures or infrastructure. The change in volume exerts stress on building foundations andother loads placed on these soils.

The most obvious way in which expansive soils can damage foundations is by uplift as they

swell with moisture increases. Swelling soils lift up and crack lightly-loaded, continuous strip

footings, and frequently cause distress in floor slabs and because of the different building

loads on different portions of a structure's foundation, the resultant uplift will vary in

different areas; such differential movement of the foundation can also cause distress to the

framing of a structure. Besides, Shallow pipes buried in the zone of seasonal moisture

fluctuation, are exposed to enormous stresses by shrinking soils. If water or sewage pipes

break, then the resultant leaking moisture can aggravate swelling damage to the nearby

structures.






27

4.8.1 Mitigation measures

The best way to avoid damage from expansive soils is to extend building foundations

beneath the zone of water content fluctuation. The reason is twofold: first, to provide for

sufficient skin friction adhesion below the zone of drying; and second, to resist upward

movement when the surface soils become wet and begin to swell.

Another way of mitigating expansive soil problems is to collect surface runoff and to limit

surface infiltration during the rainy season; proper design and construction of surface

drainage systems will be crucial.

Soils shrink and swell - because the moisture content changes from dry to moist and vice

versa. Thus, shrinking and swelling can be reduced if the moisture content is kept stable.

Damage from shrinking and swelling soils can also be reduced or prevented with proper

foundation design. Several design alternatives are:

–Drilled pier and beam: Drilled pier and beam systems are designed to isolatethe structure from expansive soil movements.

– Stiffened slab-on-grade: Designed to provide a rigid foundation to protect

the structure from differential soil movement.

– Monolithic wall and slab: Designed to provide a rigid foundation to resist

differential soil movement.

– Modified continuous footings, walls, and basement construction. Design to

provide a rigid foundation to resist differential soil movement.

4.8.2 Treatment of Expansive Soils

To avoid damage from the expansive soils, soils can also be treated in different ways, both

before and after construction. The different treatment techniques are:

• Removal of expansive soil and replacement with a non-expansive material is a

common method of reducing shrink-swell risk. If the expansive soil or stratum is

thin, then the entire layer can be removed.

• Pre-wetting a site can eliminate an expansive soil problem if the high moisture

content can be maintained.

• Chemical treatment: Lime stabilization can be used.






28

5 FOUNDATION ANALYSIS

5.1 Introduction

Foundation analysis refers to the determination of the bearing layer and depth, allowable

bearing pressure and type of foundation that could be adopted safely and economically.

Factors such as the load to be transmitted to the foundation and the subsurface condition ofthe soil have been considered in selecting the foundation type.

As can be observed from the detailed geotechnical logging, the subsurface formation of the

project site comprises of three different geotechnical layers:

The top most part of the building site is covered by medium stiff, dark grey, highly

plastic Silty CLAY with a maximum thickness of 2.40m (Layer 1).

Medium stiff to very stiff, grayish brown, moist and highly plastic Silty CLAY soil. It is

encountered in all the boreholes underlying the top layer 1 (Layer 2).

Light gray, moderately to slightly weathered, dominantly with closely spaced joints,

fine grained BASALT; this layer is encountered in four of boreholes only, i.e. BH-151to BH-154 (Layer 3).

Layer 1 is the high plastic soil that is unsuitable as foundation soils as far as the nature of the

material is concerned. Among the three layers the possible seat of the foundation footings

is Layer 2, which is highly plastic Silty CLAY soil; but, the impact of the expansive soil on the

foundation shall be considered and appropriate mitigation measures and treatments shall be

met.

Allowable bearing pressures for the selected foundation layers shall be discussed based on

correlation of the relative compaction of the insitu ground as indicated from SPT and

laboratory UCS tests.

5.2 Isolated Foundation

Isolated footings are the simplest to construct and economical type of foundations. The

allowable bearing capacity of these types of footings can be determined using different

methods; in the different methods insitu tests (SPT N-Values), laboratory tests and visual

identification can be used to determine the allowable bearing capacities for this project.

5.2.1 Bearing Pressure Based on UCS

Unconfined compressive tests were conducted on twenty four undisturbed soil samples (8

on G+4 and 16 on G+7 Building sites) taken from all the boreholes sunk. Unconfined

compression tests are conducted to determine the undrained shear strength value, Cu of thesoil. The undrained shear strength of the soil, Cu, can be determined from unconfined

compressive strength (UCS) of soil as follows:

Cu

The net ultimate bearing pressure for vertical loads on clay soils is normally computed as a

simplification of either the Meyerhof or Hansen bearing capacity equations (Bowles, 1997).

For cohesive soils, changes in ground water levels do not affect theoretical ultimate bearing

capacity. For the most critical stability state (Ø = 0), which is created when the foundation

load is applied so rapidly, the immediate bearing capacity is independent of the location of

the water table. This is in contrast to the long term stability in which the value of the drained

= ½ UCS






29

shear strength cd, and drained friction angle Ød should be considered. The ultimate bearing

capacity of the footings can be calculated using:

qult = 5.14Cu(l + s'c + d'c) + q

Where qult = Ultimate bearing capacity in unit of Cu

Cu = Undrained shear strength of soil

s'c = Shape factor = 0.2(B/L)

d'c = Depth factor = 0.4(D/B)

q = Overburden pressure which is neglected since there will

probably be footing excavation.

B = Width of the foundation

L = Length of the foundation

D = Depth of the foundation

Designing a foundation on the basis of ultimate bearing capacity, a suitable factor of safety

should be used to determine the allowable pressure so that the foundation system may besafe against shear failure. For isolated footing foundations, a factor of safety of 2 to 3 is

commonly used under normal loading conditions. Thus, for the project buildings we have

taken a factor of 3.0. The allowable bearing capacity is determined using:

qall = qult

Table 5-1: Allowable Bearing Pressure Based on UCS Test Result of Soil Samples for Layer2.

/FS

The allowable bearing capacities calculated from UCS results are presented in Table 5-1

below. Here, the bearing capacity is computed for different widths of foundation at a depth

of 2.5m on Layer 2; average Cu value, within the blocks, has been taken for the bearing

capacity analysis.

BH-ID BLOCK

NO Width,

B in m

Depth

( m)

OB,

Mean

Ƴbulk

KN/m3

Mean Cu

(KPa)

OB.

Press.q,

KPa

qa (KPa),

Hansen


Around BH-

143, & BH-144B-299

2

2.5

17.30 26.23 43 84

2.5 17.30 26.23 43 86

3.0 17.30 26.23 43 83

Around BH-

145 &BH-146 B-303

2

2.5

16.24 25.27 41 81

2.5 16.24 25.27 41 833.0 16.24 25.27 41 80

Around BH-

147 &BH-148B-304

2

2.5

16.34 26.18 41 84

2.5 16.34 26.18 41 85

3.0 16.34 26.18 41 82

Around BH-

149&BH-150B-308

2

2.5

16.81 28.26 42 89

2.5 16.81 28.26 42 91

3.0 16.81 28.26 42 88


Around BH-

131 &BH-132 B-306

2

2.5

17.01 38.52 43 117

2.5 17.01 38.52 43 120

3.0 17.01 38.52 43 115






30

Around BH-

133 &BH-134B-305

2

2.5

16.89 32.15 42 100

2.5 16.89 32.15 42 102

3.0 16.89 32.15 42 99

Around BH-

135 &BH-136 B-302

2

2.5

17.29 29.78 43 94

2.5 17.29 29.78 43 96

3.0 17.29 29.78 43 93Around BH-

137 &BH-138 B-301

2

2.5

16.95 32.11 42 100

2.5 16.95 32.11 42 102

3.0 16.95 32.11 42 98

Around BH-

139, BH-140 B-300

2

2.5

18.40 35.84 46 111

2.5 18.40 35.84 46 114

3.0 18.40 35.84 46 109

Around BH-

141 &BH-142B-298

2

2.5

16.74 48.84 42 144

2.5 16.74 48.84 42 148

3.0 16.74 48.84 42 142

Around BH-151 &BH-152

B-309

2

2.5

17.08 38.85 43 118

2.5 17.08 38.85 43 121

3.0 17.08 38.85 43 116

Around BH-

153 &BH-154 B-307

2

2.5

16.82 35.28 42 108

2.5 16.82 35.28 42 111

3.0 16.82 35.28 42 107

5.2.2 Bearing Pressure Based on SPT N-Values for Isolated square Footing

The SPT N-values/300mm should be adjusted for different factors before employing them

for computing the allowable bearing pressure. The SPT N-values are converted to N70

standard energy ratio value (Bowles, 1988) using:

N'70 = CN x N x n1 x n2 x n3 x n4

Where N'70 = adjusted N

CN = adjustment for overburden pressure

(p''o/p'o)1/2

p'o = overburden pressure

p''o = reference overburden pressure (95.76kPa or

1.0kg/cm2)

n1 = Er/Erb (where Er is average energy ratio that depends onthe drill system and Erb is the standard energy ratio).

n2 = Rod length correction

Rod length > 10 m = 1,

Rod length 6-10 m = 0.95,

Rod length 4-6 m = 0.85,

Rod length 0-4 m = 0.75

n3 = sampler correction (1.00 in this case)

n4

= borehole diameter correction (1.00 in this case)






31

The depths below NGL, SPT N-values, adjusted N-values (i.e., N’70

Table 5-2: Measured and adjusted SPT N values

) and the calculated design

N-values are given below.

Sr.

NoBH-ID Depth (m)

SPT N-values/ 300mm Adjusted N-values

Around G+4 Building

1 BH-143

1.55-2.00 3 3

3.10-3.55 5 5

4.55-5.00 9 9

6.00-6.45 11 10

7.55-8.00 15 12

9.00-9.45 15 12

2 BH-144

1.50-1.95 4 4

3.00-3.45 5 5

4.50-4.95 5 56.00-6.45 8 7

7.50-7.95 9 7

9.00-9.45 9 7

3 BH-145

1.55-2.00 5 5

3.10-3.55 6 6

4.55-5.00 8 8

6.00-6.45 10 9

7.50-7.95 12 10

9.00-9.45 13 10

4BH-146

1.55-2.00 4 4

3.10-3.55 5 5

4.55-5.00 7 7

6.00-6.45 8 7

7.55-8.00 9 7

9.00-9.45 11 9

5 BH-147

1.55-2.00 5 5

3.10-3.55 4 4

4.55-5.00 10 10

6.00-6.45 7 6

7.55-8.00 12 10

9.00-9.45 13 10

6 BH-148

1.55-2.00 4 4

3.10-3.55 6 6

4.55-5.00 10 10

6.00-6.45 9 8

7.55-8.00 7 6

9.00-9.45 8 6

7BH-149

1.55-2.00 4 4

3.10-3.55 6 6

4.55-5.00 11 11

6.00-6.45 12 11

7.55-8.00 14 12






32

Sr.

No BH-ID Depth (m) SPT N-values/ 300mm Adjusted N-values

9.00-9.45 15 12

8BH-150

1.55-2.00 13 13

3.10-3.55 8 84.55-5.00 12 12

6.00-6.45 17 16

7.55-8.00 18 15

9.00-9.45 18 14

Around G+7 Building

1 BH-131

1.55 – 2.00 3 3

3.00 - 3.45 7 7

4.50 – 4.95 9 9

6.00 - 6.45 10 9

7.50 – 7.95 11 9

9.00 - 9.45 9 7

10.5 - 10.95 10 7

12.00 - 12.45 11 7

13.5 - 13.95 10 6

2 BH-132

1.50-1.95 5 5

3.10-3.55 6 6

4.50-4.95 6 6

6.00-6.45 6 6

7.55-8.00 7 6

9.00-9.45 8 6

10.50-10.95 9 612.00-12.45 9 6

13.50-13.95 11 7

3 BH-133

1.55-2.00 3 3

3.00-3.45 7 7

4.50-4.95 6 6

6.00-6.45 5 5

7.50-7.95 7 6

9.00-9.45 8 6

10.50-10.95 9 6

12.00-12.45 10 6

13.50-13.55 11 7

4 BH-134

1.55-2.00 5 5

3.00-3.45 7 7

4.50-4.95 9 9

6.00-6.45 15 14

7.55-7.95 8 7

9.00-9.45 7 6

10.55-11.00 8 6

12.00-12.45 8 5

13.55-14.00 10 6

5 BH-135 1.50-1.95 4 4






33

Sr.


3.00-3.45 5 5

4.50-4.95 6 6

6.00-6.45 8 77.55-7.95 10 8

9.00-9.45 13 10

10.50-10.95 8 6

12.00-12.45 10 6

13.50-13.95 12 7

6 BH-136

1.55-2.00 4 4

3.00-3.45 8 8

4.50-4.95 9 9

6.00-6.45 10 9

7.55-7.95 10 8

9.00-9.45 11 9

10.50-10.95 12 9

12.00-12.45 11 7

13.50-13.95 13 8

7 BH-137

1.50-1.95 3 3

3.00-3.45 6 6

4.50-4.95 7 7

6.00-6.45 9 8

7.50-7.95 8 7

9.00-9.45 10 8

10.50-10.95 12 912.00-12.45 12 8

13.50-13.95 11 7

8 BH-138

1.50-1.95 3 3

3.00-3.45 7 7

4.50-4.95 11 11

6.00-6.45 11 10

7.50-7.95 10 8

9.00-9.45 6 5

10.55-11.00 10 7

12.00-12.45 11 7

13.50-13.95 13 8

9 BH-139

1.50-1.95 4 4

3.00-3.45 6 6

4.50-4.95 7 7

6.00-6.45 12 11

7.50-7.95 7 6

9.00-9.45 10 8

10.50-10.95 11 8

12.00-12.45 11 7

13.50-13.95 13 8

10 BH-140 1.50-1.95 5 5






34

Sr.


3.00-3.45 5 5

4.50-4.95 8 8

6.00-6.45 9 87.50-7.95 10 8

9.00-9.45 10 8

10.50-10.95 11 8

12.00-12.45 10 6

13.50-13.95 12 7

11 BH-141

1.50-1.95 3 3

3.00-3.45 6 6

4.50-4.95 7 7

6.00-6.45 10 9

7.50-7.95 10 8

9.00-9.45 11 9

10.50-10.95 9 6

12.00-12.45 11 7

13.50-13.95 12 7

12 BH-142

1.55-2.00 4 4

3.00-3.45 6 6

4.50-4.95 8 8

6.00-6.45 10 9

7.50-7.95 8 7

9.00-9.45 11 9

10.50-10.95 9 612.00-12.45 10 6

13.50-13.95 11 7

13 BH-151

1.55-2.00 5 5

3.10-3.55 9 9

4.50-4.95 11 11

6.00-6.45 14 13

7.55-8.00 16 13

9.00-9.45 18 14

10.55-11.00 19 13

12.00-12.45 19 12

14 BH-152

1.55-2.00 5 53.10-3.55 8 8

4.55-5.00 11 11

6.00-6.45 12 11

7.55-8.00 16 13

9.00-9.45 17 13

10.55-11.00 50 32

15 B-153

1.55-2.00 5 5

3.10-3.55 11 11

4.55-5.00 11 11

6.00-6.45 12 11






35

Sr.


7.55-8.00 7 6

9.00-9.45 8 6

10.55-11.00 16 11

16 B-154

1.50-1.95 7 7

3.10-3.55 8 8

4.50-4.95 10 10

6.00-6.45 14 13

7.50-7.95 15 12

9.00-9.45 18 14

10.55-11.00 11 8

12.00-12.45 14 9

After adjusting the N-values based on the above formula, the design N-values are calculated

as the average of N-values which are found in between ½ B above and 2B below the

proposed foundation depth. B is the width of the foundation.

The bearing capacity for the soil layer is calculated from the SPT N- values using Meyerhof’s

equation as follows (Bowles, 1997):

qa = N'/F2(1 + F3/B)2Kd , B>F4

Where qa = Allowable bearing pressure for

Settlement limited to 25 mm.

Kd = 1+0.33D/B < 1.33

F2 = 0.06

F3 = 0.3

F4

= 1.2

B = Width of foundation

D = Depth of foundation

The following allowable bearing pressures are calculated from a depth of 2.0 to 3.0m below

the ground level for different width for settlement limited to 25mm. Here, the SPT on rock

head is considered as refusal and given N value of 50 for bearing capacity computation, for

other depths see Annex 3.






36

Table 5-3: Allowable Bearing Pressures Based on SPT N-Value

BH-IDBlockNumber

Depth offoundation

belowNGL (m)

Width of foundation (B), m

2 2.5 3 4 5

Al lowable Bearing Capaci ty (Qall) in Kpa

Around G+4 Building

Average ofBH-143,144 B-299

2.0 169 160 168 163 154

2.5 178 190 175 169 159

3.0 203 213 195 175 163

4.0 224 223 215 205 172

Average ofBH-145,146

2.0 179 170 169 164 155

B-303

2.5 189 191 177 170 160

3.0 208 208 196 176 164

4.0 219 219 211 202 173


2.0 187 177 171 161 152

B-304

2.5 197 193 178 166 156

3.0 219 217 192 172 161

4.0 221 214 206 197 170


B-308

2.0 242 230 222 207 196

2.5 255 251 238 215 202

3.0 257 255 242 222 207

4.0 269 261 252 240 219

Around G+7 Building

Average ofBH-131,132 B-306

2.0 176 168 161 148 140

2.5 186 182 168 154 145

3.0 209 200 177 159 148

4.0 211 196 191 178 154


2.0 193 183 167 149 137

2.5 203 188 174 152 141

B-305 3.0 232 208 178 157 145

4.0 219 199 192 174 152


2.0 183 174 170 164 153

2.5 193 192 180 170 160

B-302

3.0218 212 197 175 162

4.0 223 222 214 197 172


2.0 194 185 178 162 160

B-301 2.5 205 202 186 173 165

3.0 244 231 193 179 169

4.0 244 224 216 210 181


2.0 192 183 173 165 161

B-3002.5 203 196 181 176 166

3.0 226 214 198 182 171

4.0 225 221 213 206 182

Average of 2.0 182 173 165 158 147






37

BH-IDBlockNumber

Depth offoundation

belowNGL (m)

Width of foundation (B), m

2 2.5 3 4 5

Al lowable Bearing Capaci ty (Qall) in Kpa

BH-141,142B-298

2.5 192 188 173 162 151

3.0 222 209 185 168 1554.0 221 216 208 190 164


B-308

2.0 234 222 221 212 232

2.5 246 250 237 223 238

3.0 280 277 254 262 245

4.0 292 288 278 304 259


B-307

2.0 244 232 211 193 186

2.5 257 238 220 199 185

3.0 284 256 231 206 190

4.0 270 254 245 227 200

The above bearing capacity analysis is computed for different depths and widths of

foundation footings for Layer 2 around G+4 and G+7 Buildings.

5.3 Allowable Bearing capacity for Mat Foundation

A mat foundation is commonly used where the base soil has a low bearing capacity and/or

the column loads are so large that more than 50 percent of the area is covered by

conventional spread footings. It is common to use mat foundations having basements both

to spread the column loads to a more uniform pressure distribution and to provide the floor

slab for the basement.

The bearing capacity values obtained for isolated foundation for the G+7 buildings may smallfor the proposed design load; in such cases, mat foundation will be the best choice. The

bearing capacity for the soil layer is calculated from the SPT N-values using Meyerhof’s

equation as follows (Bowles, 1997):

qall = (N55/0.08)( Ha/25)Kd For Mat foundation

Where qa = Allowable bearing pressure.

Kd = 1+0.33D/B < 1.33

∆Ha = Allowable settlement (In our case 75mm)

F2 = 0.08

F3 = 0.3F4 = 1.2

B = Width of foundation

D = Depth of foundation

The following allowable bearing pressures are calculated at a depth of 3.00m below the

natural ground level for different widths for settlement limited to 75mm. A permissible

settlement of 50, 75 and 100mm are recommended by different authors and standard

(Bowles, EBCS, U.S. Army Corps etc).






38

Table 5-5-4: Allowable Bearing Pressures for Mat foundation Around G+7 Buildings

BH-ID

Width, m

10 15 20 25 30 35 40 45 50 55 60

Allowable Bearing Capacity

BH-131&132 288 280 275 273 271 270 269 268 268 267 267

BH-133&134 288 280 275 273 271 270 269 268 268 267 267

BH-135&136 288 280 275 273 271 270 269 268 268 267 267

BH-137&138 288 280 275 273 271 270 269 268 268 267 267

BH-139&140 288 280 275 273 271 270 269 268 268 267 267

BH-141&142 288 280 275 273 271 270 269 268 268 267 267

BH-151&152 495 480 472 468 465 463 461 460 459 458 457

BH-153&154 371 360 354 351 349 347 346 345 344 344 343

5.4 Bearing Capacity using Settlement Criterion

As far as the properties of the project soils concerned, as depicted from laboratory tests

settlement shall have to be addressed properly.

Compressibility and stiffness of cohesive soil is strongly strain level dependent. But in

addition, it is also influenced by the relative rates of loading and drainage of excess pore

pressure. Compressibility and stiffness of cohesive soil is commonly expressed in a number

of ways:

• Compression Index (Cc)

• Coefficient of volume compressibility (mv)

• Undrained Young’s Modulus (Eu)

• Drained Young’s Modulus (E’)

The Compression Index (Cc) is routinely used in the calculation of settlements of normally

and lightly over-consolidated clays. The predicted compression of such materials is strongly

dependent on the value of pre-consolidation pressure used in the calculation.

In the design of any foundation, one must consider the safety against bearing capacity

failure as well as against excessive settlement of the foundation. In the design of mostfoundations, there are specifications for allowable levels of settlement.

The settlement of a foundation can have three components: (a) elastic settlement Se, (b)

primary consolidation settlement Sc, and (c) secondary consolidation settlement Ss. The

total settlement St can be expressed as:

St= St + Sc + Ss

For any given foundation, one or more of the components may be zero or negligible.

Consolidation settlement, Sc, is a time-dependent process that occurs due to the expulsion

of excess pore water pressure in saturated clayey soils below the groundwater table and is

created by the increase in stress created by the foundation load.






39

The consolidation settlement Sc due to this average stress increase can be calculated as

follows:

Dh= Cc'H[log(Pf/Po)]/(1+eo)

Consolidation test had been conducted on soil sample collected from the surrounding area

for consolidation settlement analysis. Table below show total settlement estimated basedon consolidation test result for different square footings with width, B located within Layer

2. The settlement is computed for Allowable Bearing Capacities ranging from 125 to 350Kpa

around BH-112 as shown in the Table below. If maximum total settlement of 50mm is

considered, it can be selected any footing widths for any required load excreted on the

foundation soil without causing unwanted settlement.

From the settlement analysis of the foundation soil (See table below), the shaded areas are

permitted both in terms of shear and settlement for the given depths and widths (taking the

maximum settlement limit i.e. 50mm).




Geotechnical Sub-Surface Investigations and Foundation Recommendations for G+4 and G+7 Condominium Building

BEST Consulting Engineers plc January 2014

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Table 5-5: Bearing Pressure analysis using settlement criteria around BH-150




Geotechnical Sub-Surface Investigations and Foundation Recommendations for G+ 4 and G+7 Condominium Building


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6 CONCLUSION AND RECOMMENDATION

As a result of field and laboratory activities carried out and the analysis of the available data

and test results, the following engineering recommendations can be made:

6.1 Subsurface geotechnical materials

Sub-surface geotechnical investigation was conducted for G+4 and G+7 Condominium

Buildings that includes drilling of twenty four (24) boreholes, sampling, insitu and laboratory

testing. Based on visual description, in-situ and laboratory test results, the sub-surface

geology is sub-divided into three geotechnical layers. Accordingly, the geotechnical

investigation revealed the occurrence of three quasi homogenous geotechnical layers.

Layer 1: Soft to Medium stiff, highly plastic CLAY

The top most part of the building site is covered by soft to medium stiff, dark grey,

highly plastic CLAY with a maximum thickness of 2.40 around BH-140 and BH-141

(Table 4-3).Layer 2: Medium stiff to stiff, Silty CLAY

This layer is characterized by medium stiff to stiff, grayish brown, moist and highly

plastic Silty CLAY soil. It is encountered in all the boreholes underlying the top layer

1; the average field SPT N-values/300mm is 9.7 (Table 4-4).

Even if the soil is class is MH in USCS, after having discussion with the client and by

considering the nature of the soil type and the hydrometer analysis result, it has

been decided to set the soil in CH soil class.

Layer 3: Moderately to slightly weathered, fine grained BASALT

This layer is characterized by light gray, dominantly slightly weathered to fresh,closely to medium spaced joints, fine grained BASALT. It is encountered in few of the

boreholes drilled (Table 4-3).

6.2 Foundation seat and allowable bearing Capacity

Among the three geotechnical layers identified, the possible seat of the foundation footings

is Layer 2, which is grayish brown, highly plastic Clayey SILT.

The bearing capacity of the bearing layer is computed based on both the SPT N-Value and

using the laboratory UCS value. The allowable bearing capacity results obtained for isolated

foundation are given in tables Table 5-1 and 5-3. Since SPT reflects the bearing capacity ofthe whole materials under the influence depth of the foundation layer i.e. 0.5B above and

2B below the foundation depth and normally reflects the actual site condition of the

foundation layer , the bearing capacity computed from SPT are more reliable for this

project.

For the G+4 buildings: Based on the geotechnical site investigation and bearing capacity

analysis, it is recommended that the foundation footings shall seat on layer 2 starting from

2.0m from the surface after considering the bearing capacities appropriate for the design

load according to table 5.3; however, the effect of the expansive soil shall be considered

and appropriate mitigation measures and/or treatment techniques (discussed in section






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4.8) shall be adopted to protect the buildings from damage due to the expansive nature of

the subsurface material.

To avoid the damage due to the expansive soils on the building, it is highly recommended

to improve the ground by replacing at least 1.5m of the subsurface material, starting from

the bearing depth (about 2.0m from the surface), with suitable non-expansive material

with a compaction of 95% standard proctor density for every 25cm fill or to extend the

depth of the foundation footings below 3.0m from the bearing depth (bearing depth is

about 2.0m from the surface) to pass the moisture fluctuation zone. In addition, proper

drainage system shall be constructed to collect surface runoff and to limit surface

infiltration during the rainy season.

For the G+7 buildings: Since the allowable bearing capacity values obtained are small (as

seen in Table 5-3 above) and the foundation material is also highly expansive soil, mat

foundation shall be used or the foundation ground shall be improved by imported non-

expansive granular material; mat foundation will be the best choice in order to avoid any

differential settlements that may happen in the building area.

A mat foundation is commonly used where the base soil has a low bearing capacity and/or

the column loads are so large that more than 50 percent of the area is covered by

conventional spread footings. Improving the foundation ground and to use mat

foundation on top of it will also be the best choice in order to avoid any differential

settlements that may happen in the building area and future failure of the buildings.

The swelling pressure test result (Table 4-8) shows that, the value of the swelling pressure is

small; the smaller value could be because of the current condition of the soil, i.e. the soil was

saturated during the test and it may already been expanded soil. Therefore , if it is possible

to maintain the current moisture content of the soil, during and after construction, the

building will be safe from the impact of swelling pressure from the subsurface material.

Table 6-1: Summary of bearing capacity for Mat foundation

BH-ID

Width, m

10 15 20 25 30 35 40 45 50 55 60

Allowable Bearing Capacity

BH-131&132 288 280 275 273 271 270 269 268 268 267 267

BH-133&134 288 280 275 273 271 270 269 268 268 267 267BH-135&136 288 280 275 273 271 270 269 268 268 267 267

BH-137&138 288 280 275 273 271 270 269 268 268 267 267

BH-139&140 288 280 275 273 271 270 269 268 268 267 267

BH-141&142 288 280 275 273 271 270 269 268 268 267 267

BH-151&152 495 480 472 468 465 463 461 460 459 458 457

BH-153&154 371 360 354 351 349 347 346 345 344 344 343

Remark: the building area is characterized by the presence of highly expansive, thick clay

soil; therefore, proper mitigation measures and/or treatment technique shall be

implemented to avoid any differential settlement that may happen in the building area






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6.3 Material for backfill and compaction criteria

In general, materials for the backfilling should be non expansive granular, not containing

rocks or lumps over 150mm in greatest dimension, free from organic matter, with plasticity

index (PI) not more than 10. The backfill material should be laid in lifts not exceeding 250mm

in loose thickness and compacted to at least 95% of the maximum dry density at optimum

moisture content as determined by modified compaction test (Proctor) (ASTM D-1557).

In case of improving the foundation by imported selected material, following any excavation

activity, and prior to any fill placement, proof rolling should be performed. It is commonly

recommend to a vibratory roller use with appropriate static weight. Compaction of the fill

materials should continue until the roller has made at least ten passes over all areas of the

site and the soils appear to be relatively firm and unyielding. Half of the roller passes should

be perpendicular to the direction of travel of the other passes. Proof rolling should be

closely monitored by the concerned engineers to observe for unusual deflection of the soils

beneath the compacting equipment. If unusual or excessive deflection is observed, then the

areas should be undercut to firm soils and backfilled with structural fill placed in maximum

one-foot thick lifts. Backfill soils should be of the same composition and be compacted to

the same criteria as structural fill soils.

In confined construction areas, proof rolling and compaction of fill materials can be

compacted with manually operated vibratory compaction equipment. But, it should meet

the compaction criteria.

The following issues should also be addresses in the compaction processes:

- The compaction work shall be checked by inspecting or testing in order to insure

that the nature of the fill material, its placement water content and the

compaction procedures are consistent with those prescribed. The commoninsitu compaction checking tests are dry density and moisture content.

- The procedures for fill placement and compaction shall be selected in such a

way that stability of the fill is ensuring during the entire construction period and

the natural subsoil is not adversely affected.

- The source of fill material shall be appropriately tested to ensure that it is

suitable and adequate for the intended purpose. The type, number and

frequency of the tests shall be selected according to the type and heterogeneity

of the material.

6.4 Settlement consideration

In the design of any foundation, one must consider the safety against bearing capacity

failure as well as against excessive settlement of the foundation. In the design of most

foundations, there are specifications for allowable levels of settlement. Here, the maximum

settlement is recommended not to exceed 50mm.

Settlement analysis was done around BH-150 based on consolidation test result. Based on

the settlement analysis of the foundation soil (tables 5-5 in previous chapter), around BH-

150, for foundation depth less than or equal to 2m, the foundation fails totally by

settlement before shear, i.e. settlement is critical; for foundation depth greater than 2.0m,

the settlement will be permissible taking the maximum settlement limit i.e. 50mm;






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however, settlement becomes critical for higher contact pressures. Generally, it can be

concluded that the foundation fails by settlement before shear; settlement is critical.

6.4.1 Seismic Consideration

In Ethiopia the afar depression and the Main Ethiopian Rift (MER) which is part of the East

African rift is where earthquake epicenters were aligned. The current volcanic activities and

the resulting geologic phenomena’s in Afar Depression and Main Ethiopian Rift (MER) are

good manifestations for tectonically dynamic nature of the zone.

Though seismic activity in the region (Addis Ababa) has not witnessed any serious

earthquakes, the project site is situated in a seismically medium dangerous part of the

country. So that it cannot rule out of the possibility of damaging earthquake from the

adjacent rift.

To generalize, the project site is located within the western rift margin of the country with

moderate seismic activity. Based on the Ethiopian Seismic Hazard Map (Gouin P 1976), the

area falls under Zone 2 corresponding earthquake magnitude (I100) of 7.4 to 6.5 on Richterscales and with ground acceleration 10.0 to 4.6% g and based on GSHAP it is located within

a Peak Ground Acceleration (PGA) zone ranging from 0.8 to 1.0m/s2

6.5 Considerations to Minimize Expansion Effect

which is also classified

as seismically moderately vulnerable for potential damage.

To minimize Expansion effects where it is not economically feasible to remove expansive

materials or to support foundations below depths of possible expansion, the effects can be

minimized as follows:

Since large seasonal changes in soil moisture are responsible for swelling, schedule

construction during or immediately after a prolonged rainy period when there will

be less potential volume change in the future.

Grade beams should contain sufficient steel reinforcement to resist the horizontal

and vertical thrust of swelling soils.

Provide impervious blankets and surface grading around the foundations to prevent

infiltration of surface water.

Locate water and drainage lines so that if any leakage occurs, water will not be

readily accessible to foundation soils thereby causing damage.

Construct proper drainage system to collect surface runoff and to limit surface

infiltration during the rainy season.

Avoid planting deep rooted trees since they will extract the moisture of the

subsurface material and cause differential settlement.

Maintenance programs shall be directed toward promoting uniform soil moisture

beneath the foundation during and after construction.

Consider stabilization of the foundation soils.






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6.6 Other Consideration

This report has been prepared for the exclusive use of Addis Ababa Housing Construction

office for G+4 and G+7 Condominium Buildings in Koye Feche III project area (Parcel 26

Building area) specific application for the geotechnical aspects. Our conclusions and

recommendations have been rendered using generally accepted standards of geotechnicalengineering and geological practices.

As a general remark, the following supplementary consideration shall be considered during

foundation construction:

• It is advisable to verify the nature and actual depth of occurrence of the bearing

layers when construction of the building starts and make adjustments if

necessary. Our conclusion and recommendation do not reflect variations in the

subsurface conditions that are likely to exist in the region of our borings and in

unexplored areas of the site. These variations are due to the inherent variabilityof the subsurface conditions of the geology of the area. If variations become

apparent during construction, it will be necessary to re-evaluate our conclusions

and recommendations based upon our on-site observations of the conditions.

• Exposure to the environment may weaken the subsurface material at the

foundation bearing level if the foundation excavations remain open for long

time.

• It is recommended to design an effective rainwater drainage system to get rid of

the consequences of the rainwater percolation into the layers. The site should

be graded so as to direct rainwater and water away from all planned structures.

If drastic changes are found on the subsurface geology and also if there is a change in the

design or the location of the proposed substructures, the recommendations presented in

this report must not be considered valid unless the changes are reviewed whether the

changes are consistent with the intent of our recommendations.

Finally, it should be noted that the results and recommendations of this report are solely

based on the site geotechnical investigation through core drilling of 24 boreholes including

insitu SPT test, collected samples and laboratory testing and assuming that the subsurface

conditions do not significantly deviate from those encountered.






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REFERENCES

1. Arora, 2003. Soil Mechanics and Foundation Engineering, 6th

2. ASSHTO, 1996, Standard Specification for Highway Brdiges, 16

edition

th

3. ASTM, American Society for Testing and Materials

edition, American

Association of States Highway and Transportation officials, D.C

4. Bowels, 1997, Foundation Analysis and Design

5. CIRIA, 1995. Construction Industry Research Information Association Report No. 143,

SPT Methods and Use

6. Donald, P. Coduto, Foundation Design Principles and Practice. Second edition

7. NAVFAC DM7-02 Foundations and Earth Structure






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APPENDICES






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Appendix 1

Borehole Logs and Cross Sections






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Appendix 2

Laboratory Test Results






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Appendix 3

Allowable Bearing Pressure Analysis

Sheets

geotechnical report and foundation recomendation

Documents