Effective Stress Analysis Of Seismic Responses Of Pile Groups In Liquefiable Soils

The study on pile-soil dynamic interaction in liquefiable soils is one of the front topics in geotechnical engineering. There are some simplified design methods for predicting the bearing capacity of the pile in liquefiable soils under seismic loading, but these methods have not been verified by physical data during the real earthquake or the model test. In order to set up countermeasures for protecting against and mitigating earthquake disaster, the research for the seismic design of pile foundation built in liquefiable soils is significant.Based on the method of effective stress analysis and the sand model of multiple-inelastic spring model, the pile-soil interaction of pile groups in liquefiable soils is discussed in this dissertation. Three models of pile-soil system were established for simulation. The dynamic response characteristics and the development rules of pore water pressure and acceleration were investigated under different boundary conditions and earthquake motions. Some main achievements of this dissertation are reached as follows:(1) The soil liquefaction has something to do with earthquake intensity. The stronger earthquake, the soil is easier to liquefy. Moreover, the upper layer soil liquefied before the lower layer.(2) The horizontal displacement of piles is obviously larger when the soil is liquefied. The stronger earthquake, the larger horizontal displacement is. The liquefaction soils sieves seismic wave selectively. Different seismic waves have different range of attenuation when they traverse the liquefaction soils.(3) The horizontal displacement and bending moments of piles are influenced by the boundary condition. According to the results, the horizontal displacement of piles is larger under viscosity boundary, but the bending moments of piles is smaller than hinge joint boundary.(4) The maximum bending moments of the pile are on 1/3 part near bottom. The maximum relative displacement between pile and soil are at the part of soil surface.(5) The speed of pore water pressure development is relative to the input seismic wave, but the boundary condition and pile interval have little influence.(6) The horizontal displacement and bending moments of the pile groups are larger than those of single pile.These results from simulation are agreement with centrifuge tests. So these results can provide references for the seismic design of pile groups foundation built in liquefiable soils. Also some results can be used to direct reinforce and treatments of pile groups on the liquefiable soils.