cigos2010-do duc thang.pdf

8/10/2019 CIGOS2010-Do Duc Thang.pdf

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PERFORMANCE OF THE

SWALLOW FOUNDATIONS ON THESOFT SOIL IMPROVED BY PILES

AND THE TOP-BASE METHOD

MSc. Do Duc Thang, Senior lecturer of University ofCivil Engineering Ha Noi

TADITS Space Structure Joint Stock Company

(Viet Nam)

The second presentation at CIGOS 2010 Conference - Paris Nov 2010The second


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Abstract:

Foundations of the multi-story buildingsconsist of number of structural

components for various functions such asdiaphragm wall, basement, pile cap andpiles. All of these components are likely to

have the bearing capacity of load.


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At present, however, the foundation design is

only consider the separate work of eachcomponent for each major function withoutconsidering the simultaneous work of all

these components as their attribute.

Moreover, most foundations have beenanalysed and designed without taking intoaccount the load reduction due to soil

removed while building the basement. Thisleads to the waste in the design andconstruction of the foundation of the multi-

storey bulidings.


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In this report, the results of researchconducted at TADITS (A company

specialized in developement newconstruction technology in Vietnam) will bediscussed with the purposes to find out anew foundation system which fully exploitsthe bearing capacity of each component

such as pile, raft, diaphragm wall and thesoft soil improved underneath the raft.


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As a result, the costs and the constructiontime significantly reduce.

This report also mentions some efficient

applications of soil improvemet method,namely Top-base, for increasing thebearing capacity of the soil and

simultaneously cut down the number ofpiles mainly used to reduce the settlement.


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1. Introduction:

In Vietnam, multi-storey buildings- about15 storeys or more- currently are under

construction in many big cities to meet theneeds, activities, trade which is rapidlyincreasing in the society.


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For the multi-storey building, they usuallyhave several basements with the function forthe car parking, or the place that supply someessential services to residents in the building.

Therefore, the foundation of such buildingsinclude many components to meet thedifferent functions of the works such as the

diaphragm wall which keeps the stablity ofthe foundation pit during the basementconstruction, the raft and the piles.


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The present popular design philosophy isto consider these components are workingindependently as if they only exist next toeach other in term of mechanics withouttaking into account the simultaneous work

as a unified structure.


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This report will concern some researchresults of TADITS as well as sucessfullyconducted at several building in VietNam

towards applying a new foundation systemthat consist of pile, raft and diaphragm wallsystems to support the multy-storeybuildings on the soft soils.

For this reason, the construction cost andtime of such buildings is significantlydroped.


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2. Contents: 2.1. Some comments:

From 1994 to 2005, TADITS Companyparticipated positively in the process ofdeveloping of the pile driving technology

by hydraulic hammer, construction thelarge diameter bored piles as well as the

inspection work to determine the loadbearing capacity of driven pile and thebored pile which has the bearing capacity

up to 2000 3000 ton.


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These have been adapting the need of the

construction of foundations for thebuildings from 20 to 30 storeys in Vietnam.

Initialy we started to do as a sub-contractor for the several foreign

foundation companies such as: BachySoletanche (France), Soilmec (Canada),

Rodio (Italy), B&B (Germany) ....Presently,we have mastered the design andconstruction work as well as the pile

quality evaluation work.


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- In 2007, we received the Technologytransfer from Top-base company TBS inKorea.

Seeing several buildings up to 30 storeyswith three basements were constructed inSeoul with the raft foundation on the top-basewithout using concrete piles we have soughtto find the feasible solution to design andconstruct such foundation with the purpose tobring economic efficiency and the safety forthe multi-storey building projects in Vietnam.


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- According to the sucessful application ofTopbase solution on the soft soil of somebuildings up to 11 storeys in Hanoi, Hai

Phong and Thanh Hoa as well as thestatic load test results of thosefoundations, it shows that the bearingcapacity of the initial soil is increased form2 to 3 times.

We have designed and constructed thissoil treatment for the following projects:


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With the building more than 10 storeys onthe soft soil, it is not feasible if we use

shallow foundation on the Top-base layerdue to the high consolidation setlementthat last for several years, even more than

hundreds of year and beyond theallowable limit value.

In this cirrcumstances, the following soilimprovement sollutions were used:


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Based on a new awareness of theadvantages when considering the

simultaneous interaction between shallowfoundation and friction piles calculated

settlement reduction theory, we proposeda new improvement soil solution by usingtop-base layers and concrete piles

underneath the shallow foundationtion.


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This solution has important role infoundation engineering practice with anessential condition is that the soft soil as

well as top-base layers must have theadequate load bearing capacity to supportthe building.


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In this case, the settlement reductiontheory will be applied to exploit the bearingcapacity of piles by using the minimum

safety factor (1) instead of 2 or 3.

This means that the bearing capacity of

piles calculated towards the settlementreduction theory will increase from 2 to 3

times.


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We have applied this new designphylosophy on some projects and get thefollowing results:

1. Some foundations designed towards theour design concepts


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(Ocean View Manor Vung Tau city - 2009)


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(Constrexim Holding 2009)


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(Yen Phuc Hospital 2010)


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(South Building of HaDo Group 60ATruong Son Ho Chi Minh city 2010)


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2. The technical and economic efficiencygained:


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Based on the tecnical datas above, it isclear that economic efficiency is high whenapplying our design concept.

For multy-storey buildings, however, using

such foundations needs to considerthoughtfully because it is rather difficult todetermine exactly the interactive

mechanism between piles, rafts and thetop-base due to their different stiffinesswhen support the building loads.


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For that reason, we proposetwo following main types of

mechanisms to ensure theirsimultaneous interaction.


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* Option 1

For buildings less than 40 meter high orwithout strict requirements of settlement,we will use the friction piles calculatedtowards settlement reduction pilemechanisms to work together with the

shallow foundation on the soft soilsimproved by top-base method.


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It is known that, friction pile increase thebearing capacity during settlement and

gain the ultimate capacity when itssettlement about 10% diammeter of pile

prior to fail if the settlement progress.

Initially, buliding load transfer to piles via

shallow foundation, then the piles willdevelop settlement.


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As a result, the soft soils improved by topbase will take partly load.

When settled, the soil consolidationhappens. This lead to the soil the bearing

capacity increased, so the actual loadtransfer upon piles reduced.

This mechnism will be irterative until thesoil is stable.


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For building over 40 meter high, or require

strict differential settlement, we willsuggest using bearing piles to reduce thesettlement and install settlement

controlling elements (SC elements) insideand upon the pile top with the purpose tocontrol and ensure the simultaneousmechanism of the pile and the shallowfoundation.


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For SC elements, we will design andfabricate to support a certain load andhave the suitable settlement like theshallow one for which the designer plan.

This mechanism is explanied as below.Firstly, because of the stiffiness of the SCelements are small comparision to the

soils improved by topbase layer, so mostof the buliding load will transfer to the soil.


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Then the soil will settle easily andconsolidate gradually due to the small

stiffiness of the SC elements.

At the time when we do not want the raft totake further load, the whole movementcycle of the SE elements finishes and the

pile caps combine firmly to the piles.


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From this point onwards, the increaingload will transfer mainly on piles and thesettlement increase very small becausethe bearing pile prevent the downwarddisplacement of the foundation.

At present, there were two projectsdesigned and calculated towards the

above design philosophy with the SCelements.


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We hope that in the nextworkshop there will have the

practical results to report tocolleagues who are interested in

this field.


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In summary, with a new design

phylosophy and the willingness to applythe suitable construction technologies(Top base method) for shallow foundation

combined piles on the soft soils, we canbring the significantly economic andtechnical efficiency in the foundation

design and construction in Vietnam.


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Thank you very much!

And I am looking forwards

to receiving your opinionson my report!

cigos2010-do duc thang.pdf

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