Numerical Simulation Of Anti-liquefaction Characteristics Of Gravel Pile Composite Foundation

Liquefiable sand soil improved by gravel pile which is the most economical and the most effective has been widely used in construction projects at present, however, relevant theory has not been advanced, especially study on the liquefaction resistance of gravel pile composite foundation has fallen far behind the engineering practice. There are two types of settlement computation method for liquefiable sand soil improved by gravel pile, one is analytical method and the other is indoor experimental method. Numerical simulation method is relatively uncommon.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)". In the paper, liquefiable sand soil under earthquake action is numerically simulated using by the three-dimensional finite difference program"FLAC3D"(Fast Lagrangian Analysis of Continua), and the influence of pile diameter, pile spacing and relative denseness of sand on the liquefaction resistance of liquefiable sand soil unimproved and improved by gravel pile is discussed, and compared with the result of shaking table tests . The result shows that:(1) The distribution of pore pressure ration is different along depth, the pore pressure ration is bigger in middle and smaller in upper and lower whether the numerical model of liquefiable soil improved by gravel pile or not .(2) The excess pore water pressure increases with the depth whether the numerical model of liquefiable soil improved by gravel pile or not .(3) The larger the relative denseness of sand, the stronger the liquefaction resistance whether the numerical model of liquefiable soil improved by gravel pile or not .(4) The effective influence drainage domain of single stone columns is a circling platform with narrow up side and wide underside . It is less than 2 times pile diameter in lower ; it is about 3 times pile diameter in middle and more than 3 times pile diameter has no obvious effect ; it has obvious effect more than 5 times pile diameter in upper.(5) In the process of earthquake action , the pore water pressure and pore pressure ratio keep stable after the peak value has reached in non-improved liquefaction soil ; but the dissipation of the pore water pressure and pore pressure ratio starts after the peak value has reached in liquefiable soil improved by gravel pile , which shows that the drainage effectiveness of stone columns is very remarkable.(6) The peak of pore pressure ration of middle and lower in the numerical model of liquefiable soil improved by gravel piles and the shaking table tests is almost equal, which proves the result of the numerical model of liquefiable soil improved by gravel piles is reliable.(7) The liquefaction resistance of the numerical model of liquefiable soil improved by gravel pile and the drainage capacity of gravel pile decrease sharply with the increase of pile spacing.