D05

Performance of Pile Foundations under Lateral Spreading eventsusing Centrifuge and Numerical Analysis〇Anurag SAHARE, Kyohei UEDA, Ryosuke UZUOKAIntroduction
Lateralspreading

duetoliquefaction induced

1-3Single Pile

10 Degree Slope

1-4

2X2 Group Pile

10 Degree Slopemechanism in piled foundations has been the cause ofPart 2: Non-liquefiable layer underlain by liquefiablemajor failure of many structures in the past earthquakes,

layer

which represents a complex loading scenario involving

Cases

Pile arrangement

Sloping Grounda soil-pile-structure interaction. Piled foundations are

2-1

Single Pile

5 Degree

2-2

2X2 Group Pile

5 Degree2-3Single Pile

10 Degree

2-4

2X2 Group Pile

10 Degree

subjected to lateral kinematic and inertial loading
generated during an earthquake shaking event leading
to the lateral spreading of soil in liquefiable soil strata.
Though most of the past research on kinematicinteraction of piled foundations focus on the mild slope
conditions so as to induce limited amount of lateral
spreading in order to study the soil-pile interaction,
which may induce significantly lesser moments leading
to a much safer design. In this paper, an effort has been
made to deal with kinematic interaction in pile group
foundation due to the mechanism of liquefaction
induced large lateral spreading events and is comparedwith the mild ground sloping condition. The soil pile
structure interaction also tends to differ based on thestiffness of soil layer and hence the failure mechanism

Centrifuge Test
The dynamic centrifuge tests were conducted at
Centrifuge facility at Disaster Prevention ResearchInstitute (Kyoto University) at 50G using the laminarcontainer. Toyoura sand is used for all the cases whichis saturated using Metolose at 50cst. The soil model isprepared by air pluviating the soil at a relative densityof 50% for the liquefiable layer and a slightly cementeddense sand is used to achieve a non-liquefiable soillayer. Figure 1 shows the typical soil model used for thecentrifuge test.

may be completely different in case of pile foundation
surrounded by the dense or non-liquefiable sand.
Different Cases studied
Following cases are considered in the present paper
Part 1: With different sloping ground condition toinduce different kinematic interactions between the pileand the surrounding soil
Table 1: Difference in sloping ground (Uniform sand)
Cases

Pile arrangement

Sloping Ground

1-1

Single Pile

5 Degree Slope

1-2

2X2 Group Pile

5 Degree Slope

Fig.1. Typical Soil Model used for the centrifuge test

Numerical Analysis
The two dimensional effective stress model FLIP
ROSE

(FiniteLiquefactionelement

analysis

Process/Responseofprogram

ofsoil-structure

systems during Earthquakes) based on finite element
theory is used for the numerical analysis. The model iswidely used to study the degree of damage suffered by
the structure resting on liquefiable ground. The soil
element is modeled using multi-spring model which
represents the nonlinear stress-strain relationship. The
pile element is modeled as nonlinear beam element.

Fig. 4. Bending Moment at the end of shaking along theNonlinear spring elements are used to consider thepile length for all 4 casesinteraction between pile and the surrounding soil. The
numerical analysis is carried out in two stages. Initiallythe static or self-weight analysis is carried out followedby the dynamic analysis to capture the soil-system
response during the lateral spreading event under theseismic loading.
Results and Discussions (for uniform ground)Fig. 5. Maximum Lateral displacement along the pilelength for all 4 cases
As seen from Fig. 2,3,4 and 5 (from the finite element
analysis), the response of single pile and 2X2 grouppile seems to differ significantly based on the different
kinematic interactions. The single pile behavior isfound to be more susceptible to large lateral spreading
Fig. 2. Single Pile with 10 degree sloping groundwith the significant increase in moments along the pilelength which may induce the formation of plastic
hinges where the moments due to kinematic interaction
alone is close to the resisting plastic moment values.
Similarly, the soil pile system response differs
significantly with the presence of denser sand layer(non-liquefiable layer) which imparts large pressure to
the pile surface with plastic hinge formation near thenon-liquefiable layer.
References

Fig. 2. Single Pile with 10 degree sloping ground

Flip Rose Ver.7.4. (2017) User Manuals.