Research On Dynamic Response Of Pile Driving

Dynamic pile driving is a discontinuous steady process. Pile will penetrate into a depth which is uncertain every impact in a short time. Besides, shearing stress on the pile-soil contact surface is discontinuous. It can be relieved after completion of each hammer blow and loaded again during the process of next hammer blow. It is a series of cyclic loading on the nodes. So it is a complex problem about dynamic response in the process of pile driving. Because dynamic analysis of pile involving geometric deformation, material nonlinear and contact nonlinear problem, it is difficult to carry out numerical simulations of pile dynamic driving.After summarized existing research methods and shortages on pile-soil interaction at the present stage, a dynamic simulation model has been set up, which is aimed to explore new methods and means in solving pile-soil dynamic interaction and continue to carry on research on pile dynamics under vertical load. Coupled with the theory of elastic stress waves, soil dynamics and nonlinear numerical computation method, a numerical model of pile and soil interaction has been set up taking advantage of a finite element analysis software ANSYS/LS-DYNA. Using the viscoelastic-plasticity constitutive model, the layered soil is simulated with nonlinear spring element. This model can simulate the whole pile penetration process by the response of a series of discrete time and space point. The factors are researched on dynamic response such as the dynamic soil strength reduction coefficient, penetration depth, pile diameter, concrete strength and the shaft resistance coefficient and so on. To further simulating slip and bond of pile-soil interface during the process of driving, a three dimensional fluid-solid coupling model is set up. The soil large deformations problem is solved in ALE technique. The transformational function of rigid-elastic body is applied to pile, which can not only improve the computational efficiency and can analysis stress distributing when pile is transformed into elastic body. To simulate the driving process of pile subjected to multiple hammer blows, a restart technology is used. The soil stress, deformation, the soil compacting and displacement effect during the driving process of pile was studied. The energy balance method has been used to verify the model. The influence factors on pile drivability are further discussed such as pile gravity, pile and soil friction coefficients, impact force, soil density and so on.