DYNAMIC RESPONSE OF 2×2 PILE GROUPS TO SOIL LIQUEFACTION IN INCLINED BASE LAYER: 1G SHAKE TABLE TESTS

Behavoir of piles subjected to soil liquefaction has not been fully understood bacause of many parameters affecting on soil-pile interaction. In this paper, dynamic soil-pile interaction of a 2×2 pile group subjected to liquefaction was studied. Physical modeling test was conducted employing a newly designed and manufactured laminar shear box and Sharif University of Technology shake table facilities. SUT shake table is a 4 m× 4 m, 3DOFs facility, capable of taking models of up to 300 kN. A laminar shear box with inner dimensions of 306 cm length, 172 cm width and 180 cm height was designed and constructed at SUT. Two seperate 2×2 pile groups (one with and another without lump mass) were installed in the model to investigate the effects of level ground liquefaction with inclined base on pile groups of 2×2 including the effect of superstructure (mass) on pile group behavior. The model of soil layers consists of a level ground liquefiable layer over a sloped non-liquefiable layer. The model was shaken with a sinusoidal base acceleration having a frequency of 3 Hz and amplitude of 0.3g. The piles and the soil at near and far fields are heavily instrumented to measure various parameters during and after shaking. The results including acceleration, displacement and bending moment of some piles are presented and discussed. Also one physical model test was conducted without soil to investigate the effects of existance of liquefiable layer on dynamic response of a 2×2 pile group. The results show that exictance of the liquefied soil did nothave significant effect on the time history of the acceleration of the pile cap but increased the amplitude of pile cap displacement by an order of 10. Also it was found that the lumped mass increased displacement, while decreased acceleration amplitude of the pile cap.

Keywords:

Soil liquefaction , Shake table , Physical modeling , Earthquake , Pile group