Centrifuge and Numerical Modelling of Sand Compaction Pile Installation

Abstract

This thesis presents the results and findings of a research study undertaken to investigate the strength set-up phenomenon due to the installation of sand compaction piles (SCPs). Centrifuge experiments were conducted where model SCPs were installed in-flight and measurements of stress, pore pressure and strength were taken. The results suggested that SCP installation has a considerable influence on the surrounding clay, where substantial strength increases were observed over time. The strength enhancement was more significant if excess pore pressures were allowed to dissipate between successive pile installations. Coupled consolidation finite element analyses were carried out to simulate the SCP installation using ABAQUS/Standard V6.6. Reasonable agreement was obtained between the numerical and centrifuge results of the radial stresses and pore pressures. The numerical results were processed to show the computed soil strength improvement profiles with radial distance from the pile, which were then used to define and quantify the extent and magnitude of the strength set-up. A logarithmic function was adopted to approximate these strength improvement profiles with various soil strength and stiffness parameters, from which a simple and practical method was proposed for predicting the SCP-induced set-up effect. As a validation exercise for the numerical simulation of time-dependent deep penetration problems, a finite element study was also performed to examine the rate effects associated with the operation of the cone penetrometer.