The Seismic Study On CFG Pile Composite Foundation In Saturated Loess

A lot of typical cases of seismic hazards and experimental study indicate that the liquefaction of saturated loess is major geotechnical seismic hazards of the loess area. However, to these three kinds of earthquake damage, there are not certain methods which can be followed yet in every engineering construction at present to avoid and prevent and cure that. With the development of economy, the building structure of the loess area of our country is more and more complicated, more and more large span bridges are build, therefore carrying on research to the seismic technology and improving the seismic performance by project measures have the important realistic meaning for earthquake prevention and natural disasters mitigation in the loess area of our country.This article is based on the engineering of CFG composite foundation on saturated loess at XueJiaWan of Inner Mongolia. It is aimed at calculation the bearing capacity value of CFG composite ground and weather the liquefaction happened and how the stress of pile changed.First, the past study in saturated loess indicates that saturated loess is more easier to liquefy than saturated sand or saturated clay. Then, it generated the liquefaction principle; the increasing model of hole pressure; the standard of saturated loess liquefaction; the distinguish method of loess liquefaction; according to analysis, the loess may liquefy when earthquake happened. Then it introduced the working principle of CFG composite ground and calculate the bearing capacity value of CFG composite ground.Second, it introduced the effective stress- dynamic analysis method on pile-soil system. The finite element method is relatively ripe, can carry on non-linear analysis and three-dimensional solid model analysis, well considers the contact status nonlinearity between pile and soil, analyses conveniently the influence for pile-soil dynamic interaction system by using different value of various kinds of mechanics parameters. So the modeling method by universal finite element procedure ADINA is discussed. These issues mainly include confirmation of the range and artificial border of the soil ground, selection of damping model, The elastio-plastic constitutive model based on Drucker-Prager yield criterion is used for the soil. The lumped mass element is used to simulate upload which could consider inertial force of upload impacted on pile-soil interaction system.According to the finite element theory and the modeling method, the three dimensional finite element solid phantom is established, Its computation content including following several parts: the pile body's static stress and strain and the bearing stratum's maximum stress; The single pile compound system's hole pressure 's response, judges whether the saturated loess level liquefied; CFG pile's stress and strain response; The dynamic response of CFG pile compound ground when the pore-water pressure is not considered , then saturated loess CFG pile compound ground is considered.According to analysis, it drawed the following conclusion: First, saturated loess CFG pile compound ground bearing capability satisfies the design value through the dead load experiment. Next, liquefies through the mechanical analysis saturated loess will liquefy in earthquake which max acceleration is 0.2g , the pile body in the load bearing process, the pile-head and the pile bottom place by the stress concentration, the pile body appears the tensile stress, but dose not achieves destruction standard. of concrete.