Research On Liquefaction Resistance Of Saturated Silty Foundation Reinforced By Multi-pile

The composite foundation with gravel columns is one of the widely used anti-liquefaction reinforcement measures.In recent years,in order to meet practical requirements,the combination of gravel columns with other types of piles are the common treatment methods in engineering practice.This paper takes the multi-pile composite foundation which is composed of CFG pile and gravel columns as an example,the anti-liquefaction effect and dynamic responses of the saturated silty foundation are analyzed.Main contents are as follows:(1)FLAC3D is used to numerically simulate the saturated silty foundation,the characteristics of excess pore water pressure,the ratio of excess pore water pressure,the horizontal acceleration,the vertical deformation and the post-earthquake settlement under the action of earthquake are analyzed.The results show that under the action of earthquake,the ratio of excess pore water pressure of saturated silt is relatively small in shallow and deep foundation and the foundation are not liquefied,the liquefaction is mainly concentrated in the middle of the foundation.(2)Dynamic responses and post-earthquake analysis of single pile composite foundation are analyzed.At the same time,the anti-liquefaction effect and dynamic responses of the composite foundation with gravel columns and CFG composite foundation under different pile parameters(pile length,pile diameter,pile spacing,permeability coefficient,pile stiffness),different seismic amplitudes and different additional loads are also studied.The results show that during the seismic period,compared with saturated silt,both composite foundation with gravel columns and CFG composite foundation can reduce or eliminate the liquefaction to some extent,and both soil settlement and the peak of horizontal acceleration have an obvious decrease,but the reinforcement effect of CFG composite foundation is more obvious.(3)Dynamic responses and post-earthquake analysis of the multi-pile composite foundation which is composed of CFG pile and gravel columns are analyzed.At the same time,the anti-liquefaction effect and dynamic responses of the multi-pile composite foundation under different pile parameters(pile length,pile diameter,pile spacing),different seismic amplitudes,different proportion of pile and different additional loads are also studied.The results show that in the multi-pile composite foundation,CFG pile is mainly to play the effect of distributing shear stress of the piles and gravel columns exert the effect of drainage.Multi-pile composite foundation can not only reduce the accumulation of excess pore pressure,eliminate the liquefaction effectively,but also reduce the vertical deformation and the post-earthquake settlement,it can have advantages of gravel columns and CFG pile respectively.Compared with the single pile composite foundation,the multi-pile composite foundation has the most significant liquefaction effect under the same conditions,whereas the dynamic deformation is smaller than that of the gravel columns composite foundation,which is larger than that of the CFG composite foundationWhen the proportion of CFG pile and gravel columns is 5 to 4,the reinforcement effect is relatively significant.It is suitable to select the pile spacing 4D for multi-pile composite foundation.