Impacts of matric suction equalization on small strain shear modulus of soils during air drying

Abstract

In this study, a weight-control bender element system has been developed to investigate the impact of matric suction equalisation on the measurement of small strain shear modulus (Gmax), during an air-drying process. The setup employed is capable of measuring the shear wave velocity and the corresponding Gmax of the soil sample in either an open system in which the soil sample evaporates freely or in a closed system that allows the process of matric suction equalisation. The comparison between measurements of Gmax in the open and closed systems revealed underestimations of Gmax when matric suction equalisation was ignored due to the non-uniform distribution of water content across the sample cross-sectional area. This study also investigated the time required for matric suction equalisation tse to be established for samples with different sizes. The experimental results indicated two main mechanisms, driving the matric suction equalisation in a closed system during an air-drying process, namely the hydraulic flow of water and the flow of vapour. While the former played the key role when the micro-pores were still saturated at the high range of water content, effects of the latter increased and finally dominated when more air invaded the micro-pores at lower water contents.