The principle and process of parallel seismic (PS) testing for the integrity testing of cemented soil columns are in- troduced in this paper. A three-dimensional (3D) finite element model (FEM) for the pile-soil system is established for impulse responses. Under saturated soil or unsaturated soil condition, several vibrating velocity-time histories at different depths in parallel hole are obtained based on the numerical simulation. It shows that the length of the pile and the one-dimensional (1D) P-wave velocity in the pile can be determined easily from the features of the mentioned velocity-time histories. By examining the slopes of the first arrival time plotted versus depth or the depth where the amplitude of the first arrival significantly decreases, the length of the pile can be determined. The effects of the 3D P-wave propagation through the saturated soil and the defect of the cemented soil column on the velocity-time histories are also investigated.
A rigorous analytical method is presented for calculating the interaction factor between two identi- cal piles subjected to vertical loads.Following the technique proposed by Muki and Sternberg,the problem is decomposed into an extended soil mass and two fictitious piles characterized respectively by Young's modulus of the soil and that of the difference between the pile and soil.The unknown axial forces along fictitious piles are determined by solving a Fredholm integral equation of the second kind,which imposes the compatibility condition that the axial strains of the fictitious piles are equal to those corresponding to the centroidal axes of the extended soil.The real pile forces and displacements can subequally be calculated based on the determined fictitious pile forces,and finally,the desired pile interaction factors may be obtained.Results confirm the validity of the proposed approach and portray the influence of the governing parameters on the pile interaction.
