Dynamic Incremental Theory For Initially Deformed Pile-Soil System

By coupling incremental elastic deformation theory with available pile-soil dynamic theory, the influences of initial stress-strain state on dynamic characteristics are studied in depth within the following fields:(1) By utilizing the incremental elastic deformation theory, the influence of initial longitudinal strain state on the dynamic response of an end bearing pile embedded in isotropic saturated soil is investigated. The governing equations for soil, based on the Biot’s poroelasticity theory, are derived in cylindrical coordinates and the pile is modeled using one-dimensional elastic theory. The analytical solutions of pile impedance, frequency response of twist angle and time history of velocity response are obtained by using the separation of variables technique. Finally, a parametric study of the influence of initial strains on the torsional impedance, twist angle and velocity response at the top of the pile is undertaken and discussed.(2) The influence of radially inhomogeneous initial strain field caused by the interfacial pressure at the interface of pile-soil medium on the dynamic response of pile and initially homogeneous soil is discussed based on the theory related to the dynamics of initially stressed bodies. The radially variation rule of shear modulus and physical parameters of soil caused by the initial strain field is deduced. The analytical solution of longitudinal dynamic impedance of soil is obtained by subdividing the soil domain into a number of annular vertical zones and introducing the plane strain and complete P-S (pile-soil) contact assumptions. A comparison between previous solutions and the present one is also carried out.. The longitudinal impedance of pile top and velocity response in frequency and time domains, are then obtained. The parametrical study of interfacial pressure on the dynamic response of P-S system is undertaken within relative lower frequency domain.(3) The longitudinal dynamic response of pile with variable section in layered soil medium is studied. The analytical solutions of longitudinal dynamic characteristics at the top of pile are obtained. The effect of layered property of initial deformation state, together with the effect of section change on the characteristics of reflected signal at the top of pile is discussed.(4) By employing "layer discrete method", the dispersion relation of torsional wave propagation in radially inhomogeneously strained pile-soil structure is investigated. The corresponding eigen-value problem is formulated and numerically solved by employing the "bisection method". The effects of influence parameters such as the number of layer and initial interface pressure is discussed according to the numerical results.