Dynamic multi-step outflow method for tests on hydraulic properties of unsaturated soils

Hydraulic properties of unsaturated soils play an important role in the studies on unsaturated soils. Because the traditional testing method takes a long time, a dynamic multi-step outflow method for fast determination of hydraulic characteristics of unsaturated soils is proposed. The method is based on the thermodynamic mixture of theoretical models proposed by Wei & Dewoolkar to derive saturation evolution equations to describe the non-equilibrium unsaturated soil by conducting two dynamic multi-step flow experiments on silt and silt clay samples. The dynamic evolution equations for saturation are soved according to the test results, and when the samples are in equilibrium state, the soil water characteristic curve and permeability function are obtained. This method does not solve the initial boundary values, just needs test data of dynamic multi-step outflow to solve the evolution equations for saturation, and thus hydraulic parameters of the samples are obtained. Compared with other methods, this method is more simple and effective.