Wave reflection characteristics at the pile tip-soil interface under low strain dynamic condition

Abstract

The wave reflection characteristics of the pile tip-soil interface under the low-strain condition were studied for exploring the possible quantitative method of detecting and judging the support conditions of the pile base. Based on the one-dimensional wave theory, a new theoretical method was proposed for studying the relation between the upward stress wave (UW) and downward stress wave (DW) under different support stiffness (k′) of the base soil. The frequency response functions (FRFs) of the displacement, velocity, and axial force were derived, simulating the soil resistance with the viscoelastic model. When the downward velocity (vd) was a semi-sinusoidal function, the upward velocity (vu) under different support stiffness was calculated. It was shown that the FRFs reflects the reflection characteristics in the frequency domain. The FRF of velocity is the same as FRF of displacement but opposite to that of force. The relation between vu/vd and k′ is antisymmetric about the horizontal axis of logarithmic coordinate, and vu/vd decreases from 1 to −1 as k′ increases from 0 to +∞. The model experiment verified the theoretical calculation results. This research is useful for the theoretical study of the reflection characteristics at the pile tip and engineering applications.