Dynamic FEM Analysis On Composite Foundation Of Rigid-Flexible Combined Pile

In recent years, the dynamic characteristics analysis of combined pile composite foundation has become the focus of one of the hot issues. Based on the field dynamic test of composite foundation under the action of blasting seismic, three-dimensional finite element model is established. According to the on-site investigation reports and the results of the field dynamic test, calculation parameters of numerical simulation can be obtained. The paper studied dynamic characteristics and dynamic time-history response of CFG pile composite foundation, cement-soil pile composite foundation and CFG core pile and cement-soil loop pile combined pile composite foundation under the action of the blasting seismic. The main conclusion can be obtained as follows:(1) According to the field test, under the same explosion energy and focal depth, the dynamic characteristics of composite foundation depend on the soil property, pile stiffness distribution and the upper part load size. The peak acceleration of each measuring point reduce significantly with the load increase on the upper, the farther the focal distance to composite foundation, the smaller the peak acceleration at the same location.(2) According to the field test, under the same explosion energy, the focal location and the type of composite foundation influences the frequency and damping ratio, however,the rule is not very clearly. The vibrate frequency and damping ratio depends on the soil property and pile property between focal and measuring points.(3) According to the on-site investigation reports, basic parameters is obtained.Compared calculation results of numerical simulation with field test, the static deformation modulus of soil is adjusted. Combined with dynamic analysis text of composite foundation,dynamic elasticity modulus and damping ratio is obtained.(4) By means of the modal analysis for composite foundation, natural frequencies of the three kinds of composite foundation is obtained, compared the frequency of cement-soil pile composite foundation and CFG core pile and cement-soil loop pile combined pile composite foundation with CFG pile composite foundation, ranges from-8.17%~8.42%.Compared the frequency of numerical simulation and the field test, ranges from-0.38%~26.97%.(5) By means of the analysis of numerical simulation and the field tests of composite foundation for different location or different depth piles and soils between pile, the rules are obtained, which is that under the same explosion energy, focal location and depth and the upper part load, the change rule of the acceleration time-history curves of numerical simulation and the field tests is similar with the distance and depth increase, and the response of numerical simulation is smaller than the response of the field tests.