Assessing the performance of prefabricated vertical drain with vacuum and heat preloading

Abstract

ABSTRACT: This paper presents the effects of vacuum and heat preloading of a prefabricated vertical drains (PVD) that are used to accelerate consolidation of soft Bangkok clay. Laboratory model tests were conducted in small-scale consolidometers with undisturbed and reconstituted specimens of untreated (PVD), vacuum-treated (vacuum-PVD) and temperature treated (thermo-PVD) materials. The flow parameters were back-calculated using the Hansbo (Ground Engineering, 12, No. 5, 16–25, 1979) method in terms of the horizontal coefficient of consolidation (Ch) and the ratio of the horizontal hydraulic conductivity in the undisturbed zone (Kh) to the horizontal hydraulic conductivity in the smear zone (Ks) or (Kh/Ks). From the results of the laboratory tests, the increased hydraulic conductivity of the smear zone of undisturbed specimens using vacuum-PVD and thermo-PVD resulted in a decrease in Kh/Ks of about 11 and 12%, and an increase in Ch of 2 and 13%, respectively. On the other hand, the increased hydraulic conductivity of the smear zone of the reconstituted specimens using vacuum-PVD and thermo-PVD resulted in a decrease in Kh/Ks of about 20 and 22%, and an increase in Ch of 34 and 54%, respectively. The horizontal coefficient of consolidation of PVD with vacuum pressure was higher than for the untreated PVD due to the increased horizontal hydraulic conductivity in the smear zone. In addition, the higher temperatures led to reduced viscosity of water, which was attributed to the increase in the horizontal hydraulic conductivity within the smear zone surrounding the PVD. The high temperatures combined with PVD yielded faster rates of consolidation and higher magnitudes of settlement.