Numerical Analysis On The Anti-liquefaction Characteristics Of Cement-soil Pile Composite Foundation

Saturated sand soil is prone to be liquefied under earthquake, which caused damage to the building or structure, How to protect sand soil liquefaction is an important subject in geotechnical engineering. Cement-soil pile is widely used in reinforcing soft foundation, construction techniques and testing of composite foundation are more mature and there is more research. Cement-Soil piles for solidating liquefied soil are currently being used by a number of practical projects, but there is a little study on the performance and strengthening mechanism of cement-soil piles, reaserch on simulating liquefaction characteristic of cement-soil pile composite foundation under earthquake is less. And, the effect of the cement-soil pile for reinforcing the liquefied sand soil is unkown.The thesis is supported by National Natural Science Foundation of China"The experimental study on mechanism of piles improving liquefiable soil (No.50578104)"and Provincial Natural Science Foundation of Shanxi"The discussion on methods for sand liquefaction estimating of compound foundation of sand pile (No.2006011046)". By the FLAC3D,different types of reinforced and un-reinforced liquefied soil model with different density are established, by the establishment of the dynamic finite difference model, pore water pressure,pore water pressure ratio and vertical displacement and surface acceleration are analyzed in non-improved and improved soil with the same density. It comes to the conclusion that: (1) In non-improved foundation, the same level soil pore pressure ratio, excess pore water pressure is basically the same, the excess pore water pressure in the same vertical plate increases with depth. Along with the increasing of density, the increasing speed of pore pressure ratio is slowing down, its peak delays in time and decreases in value;(2)Compared with the un-reinforced foundation, the pore water ratio in the region close to the cement-soil pile is slashing, range the central influence area is not declining, range the edge influence area is falling a little; (3) Z-displacement of the soil reinforced by Cement-soil pile reduces, it shows that the overall strength of the soil is improved after reinforced, liquefaction is inhibited effectively; (4)Surface acceleration of the foundation reinforced by Cement-soil pile is higher than that of the un-reinforced, under the same condition, the higher the density is , the greater the surface accelerationv is; (5)The maximum Shear stress appears in the lower pile, it should be taken seriously.The result obtained with experiments agrees with the finite different result, the rationality of the numerical model is improved, so as to lay the foundation to establish numerical calculation method of seismic response on liquefied soil reinforced by piles.