In-Situ And Laboratory Investigations Of Stress-Dependent Permeability Function And SDSWCC From An Unsaturated Soil Slope

Abstract

Permeability function of an unsaturated soil, k(y), where y is suction, is a vital hydrogeological property that governs seepage in various geotechnical problems. Owing to considerably long test duration, direct measurement of k(y) is often avoided if at all possible. Instead, numerous semi-empirical predictive equations have been developed to determine k(y) indirectly. However, effects of drying-wetting history and net normal stress are not generally considered, casting doubts on the validity of some semi-empirical predictive equations. In this paper, stress-dependent k(y) and stress-dependent soil-water characteristic curve (SDSWCC) of a decomposed silty clay are investigated under both field and laboratory conditions. To measure effects of drying and wetting on k(y) directly, an in-situ one-dimensional (1D) permeability test was carried out using the instantaneous profile method on a saprolitic hillslope in Hong Kong. In the laboratory, a new 1D stress-controllable soil column was developed to determine stress-dependent k(y) and SDSWCC on block samples taken from the same hillslope. Effects of drying-wetting cycle(s) and net normal stress on measured stress-dependent k(y)s and SDSWCCs are explored and analysed. By comparing measured and predicted k(y)s, the predictability of some existing semi-empirical equations is evaluated.