Time-lapsed shear-wave velocity (V-s) tomographic images and stress in sand surrounding displacement pile during setup

摘要

This study reports model pile tests designed to characterize the underlying mechanisms of driven pile setup in dry sand by means of stress measurement with the tactile pressure sensors and spatio-temporal, shear-wave velocity (V-s) distributions using an automated high-speed tomographic imaging system. The pile-load test results demonstrate a distinct increase in the pile shaft resistance after pile setup. The measured stress and V-s in the soil surrounding the pile suggest the increase in the radial effective stress during pile loading Delta sigma(rp)', as a result of the aging-induced stiffness increase, is the dominant mechanism of pile setup. The spatio-temporal evolution of V-s distributions reveals that during initial aging (before pile installation), V-s is similar at any distance to the pile shaft and exhibits a similar aging rate S-0 in terms of stiffness increases. After pile installation, the soil exhibits a higher aging rate S-1. In addition, the ratio S-1/S-0 decreases with increasing distance from the pile shaft. A lower initial V-s and a higher aging rate S-1 are also observed for the measurements at the three sensing layers of different depths, suggesting that more soils disturbed by pile installation tend to recover at a relative higher aging rate.