Recent Developments of PVD Soft Ground Improvement: Laboratory Test Results and Simulations

Abstract

This chapter focuses on the recent developments of soft ground improvement using prefabricated vertical drain (PVD) combined with surcharge, vacuum, and heat preloading in shortening the consolidation time. The laboratory tests were conducted in a large-scale consolidometer with reconstituted specimens using PVD combined with surcharge (PVD only); PVD combined with surcharge and vacuum pressure (Vacuum-PVD); PVD combined with surcharge and heat up to 90 °C (Thermo-PVD); and PVD combined with surcharge, vacuum pressure, and heat up to 90 °C (Thermo-Vacuum-PVD). Analyses were carried out to determine the flow parameters by back-calculation in terms of the horizontal coefficient of consolidation (C h) and the ratio between the horizontal permeability in the undisturbed zone (K h) to the horizontal permeability in the smear zone (K s) or (K h /K s). The C h values for reconstituted specimens with PVD, Vacuum-PVD, Thermo-PVD, and Thermo-Vacuum-PVD were 1.93 m2/year, 2.23 m2/year, 4.17 m2/year, and 4.38 m2/year, respectively, with corresponding K h /K s values of 3.0, 2.7, 1.4, and 1.1, respectively. The results of FEM numerical simulations using ABAQUS software yielded good agreement with the measured settlements and excess pore water pressures. Moreover, the higher temperatures resulted in reduced viscosity of water, which resulted in the increase in the horizontal permeability. The Thermo-PVD and Thermo-Vacuum-PVD resulted in faster rates of consolidation and higher magnitudes of settlement because of the reduction of the drainage retardation effects in the smear zone surrounding the PVD, which resulted in the reduction of K h /K s and increased coefficient of horizontal consolidation, C h.