Better Zsoil,Better Geotecnical Analysis

Solve complicated geotechnical problems caused by design changing of a high rise building under construction with zsoil.pc

YIN JI 1,2 Email:geofem@126.com

1. SGIDI 2.GEOFEM

• Background – When the foundation slab has been constructed,

the proprietor decide to change architectural design.

– The project suspended for 6+ months.

• PART 1: Geotecnical problems encontoured

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先 锋 电 机 厂

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不准测量2010年10月

上 海 第 一 机 床 厂 有 限 公 司

启迪大厦 To basement sideline 37.1m

To building sideline 12.9m

Basement sideline of our project

Basement sideline of building A,3~27F Basement sideline

of building B,3~18F

Tower location (27F)

B2F, 7.0m depth

Surrounding environment of the project

2014/8/29

• Rendering before design changing – 15F + B3F – construction eara 107541m2

• Rendering after design

changing – 27F(100m) + B3F

• They are totally different!

2014/8/29

when the foundation slab has been constructed, the proprietor decide to change architectural design.So the project suspended for 6+ months.

reinforced concrete strut

Steel lattice column to support the strut

The current status of the project

slab, 1.2~1.8m thick

2014/8/29

building location(15F eara) before design changing

building location(27F eara) after design changing

1.2~1.8m thick slab will be removed and thickened to 2.3m. area of this

region is about 2100m2

Main building location of old and new design

Ahout 117 CIP will be added here.

35m

65m

2014/8/29

Tower pile，CIP,0.8m dia.,40m length,compressive bearing

capacity Ra=3600kN

Podium tension pile，CIP,0.6m dia.,31m length,tension bearing

capacity Ra'=1400kN

Tower pile of Building A，PHC500, 20m length,compressive bearing

capacity Ra=1400kN

Podium tension pile of Building A，PHC500, 20~24m length,tension bearing capacity Ra'=420~480kN

Pile information

Sandy silt

clay & silty clay

Sandy silt interbedded with silty clay

silt clay

2014/8/29

confined aquifier,about 6m thick, water head measured -2.0m (about 6m below the surface)

bottom of foundation pit

artesian head now Dewatering is necessary for the special geological section

Added CIP (bore hole) penetrate confied aquifier.

Artesian head must be lowered to bottom of the slab for safety

consideration.

target artesian head

cement soil mixing pile waterproof curtain

CIP,0.9m dia.,22.7m length,0.2m net spacing

Reinforced concrete strut

cement soil mixing pile soil improvment

Sectional view of retaining structure of foundation pit

3rd layer strut (partially) must be removed, otherwise there is no enough space for

piling equipment.

• current 1.2~1.8m thick slab will be removed(demolition blasting)

• 3rd strut(partially) will be removed before the contact "new" slab can sustain lateral force

• artesian head must be lowered to the bottom of the slab

• removing lateral support will cause – internal force increase of

retaining structure and strut system

– additional displacement of retaining structure and surrouding environment

• dewatering will cause – additional

displacement(settlement) of surrouding environment ,especially the builing stand on the confined aquifier (Building A).

• PART 2: Analyze geotecnical problems with ZSOIL.PC

Overall analysis and Pre-analysis

• To gain the current or initial state of internal force (stress)and displacement of foundation slab, retaining structure,strut system and building nearby, the entire construction stage should be modelled.

• Deformation+Flow is necessary to analyze displacement/settlement of surrouding environment caused by dewatering.

• To gain credible and valuable displacement information, small stiffness model, such as HS-s model is necessary.

Overall analysis and Pre-analysis

• A super structure-foundation-soil model is adopted to assess the settlement of the surrounding building acurately.

• Special attention should be paid to dewatering well simulation effectively and easily.

• According to engineering experience, pumping confined water will have an impact on the far boundary.So boundary of the model shoul be more far compared with simple Deformation analysis.

FE model

2015m

70m

1262m

building A. 3~27F excavation of

our project

refined mesh coarse mesh

mesh tying here to combine incompatible mesh

underground strutcture of builing A

shear wall column

piles

super structure-foundation-soil model

of builing A

only piles under tower are considered

trestle

retaining structure, shell hinges are used to set free rotational DOFs

piles stand on confined aquifier

strut dewatering well

retaining wall, CIP， set free DOFs

between two "piles".

how to model dewatering effectively and easily?

• model dimension should be large enough? – boundary effect is significant for some software

solving dewatering problems. – model dimension will be 2015m×1260m×70m

here.

• gradient mesh and mesh tying technology is adopted to reduce number of mesh.

how to model dewatering effectively and easily?

• dewatering wells are "glued" to the overall model with kinematic constraint. – I'd like to call it "flying well". It means you can

place it anywhere you want without remeshing the overwall model.

– "flying well" can be prepared in a seperate file, and then imported to the overall model.

– dewatering plane can be adjusted easily by changing the "flying well" file.

dewatering well type A: drainage the shallow dive.only

filter tube is modelled.

dewatering well type B: lower the artesian head to 14m below the

surface.only filter tube is modelled.

dewatering well type A: drainage the shallow dive

dewatering well type B: lower the artesian head to 14m below the surface.

foundation slab

filter tube

confined aquifier

filter tube

coarse sand

high quality clay ball

clay steel tube

dewatering well structure

only filter tube part is modelled as "flying well"

dewatering plane I:only dewatering wells(type A + type B) are modelled.

type A wells are hidden here.

inactive

inactive

inactive inactive

inactive

inactive

inactive

Drive type:Deformation + FLOW

water head for dewatering well type A

water head for dewatering well type B 3

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Analysis stages

stage 1: initail state stage 2: 1st layer strut

stage 3: 1st layer soil stage 4: 2nd layer strut

Analysis stages

stage 5: 2nd layer soil stage 6: 3rd layer strut

stage 7: 3rd layer soil stage 8: bottom of excavation

Analysis stages

stage 9: foundation slab and piles stage 10: (1)remove 3rd strut entirely; (2)remove 1.2~1.8m thick foundation slab(about 2100m2); (3) dewatering, lower the artesian head to 14m below the surface

moment of retaining wall

Max.715kN.m,before removing 3rd strut Max.864kN.m,after removing 3rd strut

Max.879kN.m,dewatering 3 months

lateral displacement of retaining structure

Max.5.34cm,before removing 3rd strut Max.5.72cm,after removing 3rd strut

Max.5.76cm,dewatering 3 months

axial force of struts

Max.7572kN(3rd strut),before removing 3rd strut

Max.5278kN(2nd strut),after removing 3rd strut

Max.5578kN(2nd strut),dewatering 3 months

Max.4050kN(2nd strut),before removing 3rd strut

contour map of total head before pumping confined water

contour map of total head after pumping confined water

contour map of total head of confined aquifier after pumping confined water (4 month)

initial artesian head is -3.0m(about 6m below the ground surface)

contour map of add. settelment of ground sruface after pumping confined water (4 month)

Max. additional settlement 2.18cm

contour map of add. settelment of building A after pumping confined water (4 month)

Max. additional settlement 14.3mm of building A

7.71mm 6.08mm

Max. 14.3mm

recharge well type C:reduce the influence of surroundings

caused by dewatering.

dewatering plane II: dewatering wells(type A + type B + type C) are

modelled.type A wells are hidden here. Drive type: Deformation+FLOW

water head for dewatering well type A

water head for dewatering well type B

water head for recharge well type C

EXF for recharge well type C,active recharge

well time=165~300

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3

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165 300

contour map drawdown of confined aquifier after lowering confined water head (4 month)

contour map drawdown of confined aquifier after lowering confined water head (4 month)

recharge well type C:reduce the influence of surroundings

caused by dewatering.

contour map of add. settelment of building A after pumping confined water (4 month)

Max. additional settlement 1.91mm

7.71mm 6.08mm

• PART 3: Site construction situation

Partially removing 3rd layer strut

Constructing dewatering

ALL type A and type B wells are running. Max.3 type C(recharge well) wells are running.

? ?

?

Removing 2100m2 foundation

Added CIPs are under construction

As if August 5th, About 50/117 CIP have been casted

Monitoring data

• As if August 5th(continued pumping about 25 days), the max. settlement of building A caused by dewatering is about 3.6mm – including ahout 2mm caused by removing

foundation slab(demolition blasting) – no recharge well running, settlement prediction is

6.1~7.7mm – all recharge well running, settlement prediction is

0.3~0.4mm

Monitoring data 混1

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settlement monitoring points tower of building A

tower of building B

Monitoring data monitoring

points

settlement monitoring points

settlement increment

（mm/day） Total

（mm） increment

（mm/day） Total

（mm） F33 0.3 -3.0 F48 -0.1 -2.1 F34 0.2 -3.0 F49 0.0 -1.8 F35 0.3 -4.0 F50 -0.2 -2.7 F36 0.2 -5.1 F51 -0.4 -2.4 F37 0.0 -5.3 F52 0.0 -2.2 F38 0.3 -4.8 F53 -0.3 -1.8 F39 0.2 -5.4 F54 -0.1 -2.1 F40 0.0 -5.7 F55 0.0 -3.6 F41 0.3 -5.6 F56 -0.3 -1.5 F42 0.0 -6.0 F57 -0.4 -2.2 F43 -0.2 -2.2 F58 -0.2 -2.8 F44 -0.1 -3.2 F59 0.1 -3.6 F45 -0.3 -1.6 F60 -0.3 -2.2 F46 0.0 -2.5 F61 0.3 -2.3 F47 0.0 -2.3 tower of building A

• PART 4: Conclusion and reflection

• conclution – ZSOIL.PC can solve dewatering problems quite

well, including pumping confined water. – Recharge well can reduce the influence of

surroundings caused by dewatering significantly. – "Flying well" can simulate real dewatering well

efficiently and easily.

• reflection – Better, or at least the options available

• steel pipe pile, instead of CIP – construction without drilling – construction without dewatering

– Why not implemented • Structural engineers do not accept the same building with

different piles – vertical support stiffness of different piles(steel pipe pile vs. CIP) are

significantly different – It is hard to reconcile stiffness differences without proper tools – This problem can be solved perfectly with ZSOIL.PC, maybe next time

– Better zsoil, better geotecnical analysis and solutions

• Acknowledgement – Thank Prof. A.Truty in terms of modelling of dewatering well.