better zsoil, better geotechnical analysis · · 2015-11-26better zsoil, better geotechnical...

Better ZSOIL,Better Geotechnical Analysis

——Practice of Pile Foundation Treatment Based on ZSOIL.PC

SYMPOSIUM : NUMERICS IN GEOTECHNICS & STRUCTURES

26 YEARS ZSOIL.PC

DATE :1-2.09.2011

YIN JI 1,2

Email:[email protected]

1.Shanghai Geotechnical Investigation & Design, co,.ltd.

2.GEOFEM

CONTENTS

Functions related to Pile Foundation Design of ZSOIL.PC Pile element Borehole Nodal link

Practice of Pile Foundation TreatmentGeneral information Challenge Pile static load test 3D FEM analysis

Acknowledgements

Functions related to Pile Foundation Design of ZSOIL.PCPile elementBoreholeNodal link

Functions related to Pile Foundation of ZSOIL.PCPile element

Mechanical Features of Pile element Pile element contains pile (structure

element ), lateral skin shear interface and toe compaction/tension interface

The interaction between pile and surrounding soil can be modeled with skin and toe interface, which comply with Mohr-Coulomb strength criterion

Pile (structure element ) inherits all the properties of beam element

Raft or trip foundation

Compaction/tension interface

Shear interface

Pile/Beam


Modeling of Pile element Hundreds of pile elements can be

generated “on objects” within several seconds, which usually imported from DXF files

Pile head can be automatically “link to” raft or trip foundation smartly, which can save us many hours to “merge” pile head and nodes of solid element

Axial force, moment and shear force can transfer from piles to raft , and vice versa

The length of each segment of pile should be compatible with the length of the soil element, not too large nor too small

If layout of piles change, import the modified DXF file again

Raft foundation

Pile head

Pile element


Parameters of pile element Parameters of pile (structure) is easy to

determine when the style of pile is selected

Parameters of skin and toe interface can inherit from surrounding soil. Default settings of the program can cope with most of the situation, however, accuracy is not too high

In-site test, like pile static load test with strain gauge set in different depth of pile, is necessary for “fine” analysis of pile foundation. We can gain strength and stiffness of skin interface though diagraph of shear displacement vs. skin force

To comply with design code, zero friction angle of pile skin interface is necessry

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14

桩身位移（mm）

侧摩阻力（kPa）

C1013

C1354

C1882

S22

Skin force of pile

Shear displacement

Ultimate Strength

Average stiffness

Determine the strength and stiffness of skin interface

Functions related to Pile Foundation of ZSOIL.PCBorehole

Complex spatial distribution of soil “Borehole” function helps to generate

complex spatial distribution of soil material easily without 3D surface generated.

It is convenient to add boreholes any time to update spatial distribution, which can save us many hours too

Functions related to Pile Foundation of ZSOIL.PCBorehole + Pile element

All for the sake of Engineers Step 1: hide all the soil above the

bearing layer of pile Step 2: “select visible faces”, then all

the face of bearing layer is selected Step 3: “Macro model\Point\Project\On

selected faces in direction”, then all the pile toes stand on the bearing layer

Step 4: move the pile toes some distance into the bearing layer if necessary

It is very convenient to “stick” hundreds of piles on the bearing layer

Functions related to Pile Foundation of ZSOIL.PCNodal link

Set the mind free Super structure can be connected to

the foundation by nodal link, without compatible mesh

Very fine structure model can be avoided, which will significantly increase the number of the elements of the whole model

Structure model can be established in another file .It can be assembled with soil and foundation when necessary.

Practice of Pile Foundation TreatmentGeneral informationChallengePile static load test3D FEM analysis

Practice of Pile Foundation treatmentGeneral information

Information of super structure Frame shear wall structure, 26F(105m),

basement 2F(16.5m depth)

This building will be discussed


Information of pile Pre-stressed concrete pipe pile(PHC), diameter 500mm, thickness 125mm,

length 30.0m(segment I :15m + segment II :15m), bearing capacity 2500kN Static piling method is used to drive the pile

Ground surface ,+30.86m

Bottom of basement ,+13.86m

Bottom of pile ,-16.14m

Pile length, 30m

PHC500, 15m length per segment

Static driving machine


Layout of piles 594 PHC piles are employed to support

the gravity of the building “grid” type layout is used, for the

bearing capacity of each pile is not high enough

The distance between two neighboring piles is 2.0m, which is the min. pile spacing according to the code for Chinese pile foundation


Information of geology conditions The site is mainly composed of silty clay (N/SPT=10~12, Ps/CPT= 1.5~2.5Mpa)

and middle sand (N/SPT=22~30, Ps/CPT= 10.0~15.0Mpa)

pile

Pile head level

Pile toe level

Sand, hard to penetrate

gravel, hard to penetrate

silty clay

6.96.96.86.8

6 6.6

6.56.46.76.7

6.8

66

6.3 6.3 6.3

6.7

6.96.4

6.86.9

6

6.86.6

6.9 6.6 6.8 6.1

6.86.86.76.86.86.9

6.96.2

6.36.4 6.5 6.8 6.6

6.2

6.4

6.7 6.7 6.9 6.8 6.3

Practice of Pile Foundation treatmentChallenge

According to the construction records, 200+ piles are shorter than design length (30m)

Irregularly distributed “hard layer” may be the reason7.07.57.0

7.47.5

7.5

7.3 7.5 7.4 7.5 7.3

7.6 7.3 7.3 7.4 7.3

7.5 7.5 7.3 7.5 7.4 7.37.77.7

7.6 7.8 7.7 7 7.1

7.2

7.2

7.3

7.3

7.4

7.27.1

7.27.17.77.67.6

7.5 7.5 7 7.2 7.2

7.17.27.17.5

7.5

7.27.27.2

7.1 7 7 7 7 7.2 7.2

7.47777

7 7 7

77

7.17.17777.2

79 piles are 7~8m shorter than design length 49 piles are 6~7m shorter

than design length


28 piles are 5~6m shorter than design length

5.75.1

5.7

5.4 5.3

5.65.6

5.5 5.5 5.6 5.8 5.3

84.55.55.35.3

5.5 5.4

5.55.5

6.2

5.5

5.95.55.15.35.9

4.7

4.3

4.6 4.5 4.4 4.5 4.5

4.3

4.2

4

44.5

4.2

4.2 4.1

4.54.14.2




3 3

3.63.73.2

33.1

3.6 3.4 3.7 3.5 3.6 3.43.13

3.1 3.2

3.4 3

3.3

3.2 3.1

3.2

3

3.4 3.3

3.43.33.1

3.1

3.4

3.0 3.2

3.2

3.9

3.9

3.2

3.7 3.7

2.4 2.4 2.4 2.4 2.4

2.42.42.42.4 2.4 2.4 2.4 2.4 2.42.4 2.4

2.1

2.82.9

2.82.8

2.7

2.4 2.3 2.7

2.92.72.82.72.8

2.7 2.8 2.8

2.1

2.9

2.1

22.7

2.6

2.12.5

2.6 2.3 2.9

2.92.82.9

2.32.7

2.32.42.42.7

2.4

2.4 2.5 2.6 2.4 2.9



It seems impossible to drive additional piles into the ground to compensate the lack of bearing capacity. There is no room left, even for only 1 pile.

It seems impossible to move to another site to construct the building. Kidding?

Maybe our client has to reduce the height of the building. maybe

With so many “short” piles, is the foundation safe enough to support the load of the building?


How to help our client? We need to know the exact load applied to each pile. Super structure-foundation-soil interaction theory can be employed to

calculate the load of each pile. Pile static load test can be used to determine the real bearing capacity of

piles with different length, especially the shortest piles. We can judge the safety factor of each pile. We can calculate the settlement of the building.

Practice of Pile Foundation treatmentPile static load test

We select 7.0~8.0m shorter piles to implement pile static load test. If the bearing capacity of the shortest piles is OK, of course ,the capacity of other piles will be OK. Pile static load test

Steel beam

Hydraulic jacks

Practice of Pile Foundation treatmentPile static load test

0 1000 2000 3000 4000 500040

30

20

10

0

settl

emen

t (m

m)

Load (kN)

7m shorter

Three 7.0m shorter piles are selected to test. We select the shortest piles to

represent the whole piles. According to the diagraph of load vs.

settlement, the max. load of the test is about 4750kN.

The current bearing capacity of the tested pile is 4750/2=2375kN. The design bearing capacity is

2500kN. The current bearing capacity is about

5% smaller than the design value. Is the current bearing capacity

enough ? What the 3d FEM analysis tell us?

Practice of Pile Foundation treatment3D FEM analysis

Some details should be considered in the analysis The effective length of the piles ,bearing layer and the depth into the

bearing capacity are very different. The distribution of stiffness of the super structure will affect the settlement

value. The distribution of stiffness of the super structure will affect distribution of

the settlement of the foundation. The thickness of the raft will play the positive role of the settlement

compatibility between raft and piles.


We implement the below when establish FEM model Pile element is used to model PHC pile. Pile skin and toe interface are

considered. The length of pile is set according to the construction record. For the

convenience of modeling, piles are classified to 7m, 5m and 3m shorter than design value.

Borehole method is used to determine the spatial distribution of soil layer. Mohr-coulomb model is used to descript soil mechanical behavior. The geometry of frame column and shear wall is set strictly according to

the structural design. The load applied to frame column and wall is set strictly according to the

structural analysis result.


Load applied on wall and Frame column according to structural calculation result


Frame columnwall

Shear wall

floor

floor

Frame column and wall are

connected to floor with “nodal link”


Raft

Piles with different length(7m,5m,3m

shorter than design length)

Bearing layer of piles


Max. settlement is about 5.85cm, which occurs at the corner of the shear wall core tube. This maybe the result of piles of

different length and irregularly spatial distribution of bearing layer.

Min. settlement is about 2.90cm. Max. settlement difference is about

2.95cm. Taking into account the width of the

raft(30m), the inclination of the building is about 0.1%.

The max. settlement and the inclination of the building meet the requirements of the standard（GB50007-2002）.


Axial force of pile head range from 520 to 2200kN. The average value is about 950kN. According to the pile static load test,

the calculated axial force of pile head (working load) is below the bearing capacity(2375kN).

The distribution of axial force of pile head is very different from our experience. According to our experience, max.

axial force of pile head usually occurs at corner and edge of the raft.

This maybe the result of piles of different length and irregularly spatial distribution of bearing layer.


Analysis Summary According to 3D Fem analysis, the bearing capacity of short piles, the

settlement and inclination of the building can meet the requirement of Chinese foundation standard (“code for design of building foundation” GB50007-2002).

It is necessary to conduct super structure-foundation-soil interaction analysisfor irregularly spatial distributed soil layer and piles with different length. Sometimes, experience from horizontally stratified ground can not be transplanted

to irregularly spatial distributed soil layer. It is too conservative to design pile foundation without consideration of the

contribution of raft. With the help of the method mentioned above, we can optimize the design of pile

foundation.

Acknowledgements

Thanks to the development team of ZSOIL.PC help from ZACE since 2011/01/03

YIN JI

Email:[email protected]

For some reasons, not all of the details is published in the PPT. Ideas maybe important than numbers for geotechnical engineers.

better zsoil, better geotechnical analysis · · 2015-11-26better zsoil, better geotechnical...

Documents