Vacuum consolidation and soil-water characteristic curves of clay

Abstract

The objectives of this study are to investigate the influence of vacuum consolidation on undrained shear strength of fine-grained soil and its soil-water characteristic curve (SWCC), as well as investigate the strength improvement differences between surcharge preloading and vacuum preloading. Kaolin was used and first made into a slurry with the addition of water. The slurry was subjected to different pre-consolidation pressures in a consolidation tank to simulate surcharge preloading. Consolidated kaolin samples were trimmed into cylindrical specimens that measured a diameter of 38 mm and a height of 76 mm. To determine the SWCC, several specimens were placed in the pressure plate device and subjected to various matric suctions. The undrained shear strength of the soil specimens was determined using unconfined compression (UC) test.

In this study, w-SWCC, θW-SWCC and S-SWCC representing SWCC in terms of gravimetric water content (w), volumetric water content (θW) and degree of saturation (S), respectively, are plotted. From S-SWCC, the air-entry value (AEV) of the soil specimens subject to different pre-consolidation pressures was determined. From the UC test, stress-strain curves were plotted for soil specimens that were subject to different pre- consolidation pressure and matric suction.

The undrained shear strength of the kaolin specimens under different pre-consolidation pressures and matric suction was determined. The UC test results were also used to determine the relationships between undrained shear strength and various parameters (degree of saturation, water content, void ratio, liquidity index and matric suction) and compared with existing literature.

Suggestions for further study are also included at the end of the report.