The effects of soil shrinkage during centrifuge tests on SWCC and soil microstructure measurements

Significant soil shrinkage occurred during SWCC (soil-water characteristic curve) measurement using centrifuge methods and thus affects the soil microstructure. This paper deals with an experimental investigation aimed at correcting for SWCC measurements with soil shrinkage considered and at studying the evolution of the microstructure induced by soil consolidation along drying path. Microstructure evolution of samples subjected to different pressure heads is determined using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) techniques. The relationship between the soil microstructural features and the soil mechanical and hydraulic properties is explained from the microstructure point of view. The results show that after the centrifugation ended, the height shrinkages of the soil samples were 10.36, 8.86, 6.39, 4.16, and 2.37 mm, while the corresponding initial bulk densities were 1.30, 1.36, 1.46, 1.55, and 1.68 g/cm³. The corrected volumetric water contents were higher than the uncorrected values at a specific pressure head. The soil shrinkage, void ratio, and degree of saturation changed at a decreasing rate as the pressure head gradually increased. These changes occurred because of the greater compressibility of the macropores, which allowed for consolidation, and because the water in the macropores was removed at a relatively low pressure head. The drastic decrease in the pore volume and the dominant diameter of such macropores inhibited further and obvious soil consolidation at a higher pressure head and inhibited the flow of water out of the soil matrix.