Study On Simplified Model Of Capillary Hysteresis Considering Air Entrapment

The soil water characteristic curve(SWCC)describes the constitutive relationship of unsaturated soil mechanics.In general,it describes the relationship between the soil suction and the soil moisture content,and more specifically,It describes the relationship between the thermodynamic potential energy of the pore water and the adsorption of the soil system.The relative indexes of unsaturated soil,such as the strength and permeability of soil,can be obtained indirectly by the soil water characteristic curve,which is widely used in practice.The traditional experiment to determine the soil water characteristic curve need more time,and the calculation model which based on the theory of unsaturated soil can be predicted conveniently.This paper introduces the theory of the internal variable theory of capillary hysteresis,which is based on thermodynamics and has a rigorous theoretical basis,can realize the calculation of any path in the hysteresis loop.However,when the model is established,the influence of inlet value is not considered,leading to the problem of infinite initial slope in the calculation result.The complete soil water characteristic curve includes the initial drying curve(IDC),the main wetting curve(MWC)and the main drying curve(MDC).After studying the drying and wetting mechanism of unsaturated soil pores,it is assumed that the pore medium is experienced after the drying/wetting cycle,when it drying again,the drainage sequence of pores doesn't change.On the basis of theory,establish a simplified model of soil water characteristic curve without any parameters and use to calculate the MDC curve.Propose a soil water characteristic curve model which can calculate for any dry and wet cycle on the basis of just knowing IDC and MWC.The model considers the effect of residual gas content,not only realizes the calculation of arbitrary high order scanning line in the main hysteretic loop composed of MDC and MWC,but also realizes the arbitrary dry/wet cycle in the range of IDC and MWC.Think the strength of the unsaturated soil considered on the basis of the saturation intensity increased the strength increment caused by the suction,proposed the unsaturated soil strength prediction formula,by defining the equivalent water content to modify the formula.Finally,the contribution of suction to unsaturated soil strength is analyzed by using the proposed formula.