Shear strength due to unsaturated conditions for vacuum consolidation works

Abstract

Vacuum Consolidation is a soil improvement technique that applies vacuum pressure to the soil which will create a negative pore-water pressure that will produce suction in the soil mass. The suction will then cause change in volume, increase in density, increase of shear strength and stability to the soil mass of the treated area. The objectives of this project were to study the effects of suction pressures on shear strength of soils and to propose ranges of suction pressure for vacuum consolidation works in Malaysia. SoilVision Version 1.0 software was used to analyse sixteen (16) soil samples by predicting their soil-water characteristic curves (SWCC) and shear strength curves based on the particle-size data. The results of the particle-size distribution curves, the soil-water characteristic curves and the variation of shear strength with soil suctions are presented. The results show that the rate and the total increment of shear strength with respect to the soil suction are influenced by the air-entry value (AEV) and the value of effective angle of friction (F’), respectively. As for the case study of Deep Water Port Project in Sarawak, the results show that the increment of shear strength with respect to suction contributes about 23.9% to 29.2% of the total increment of the shear strength; the rest comes from the effect of the consolidation of the soil layers. The ranges of vacuum pressures with respect to the desired shear strength for soils of various effective angles of friction are also proposed for vacuum consolidation works.