Abstract:At present,the coefficient of earth pressure at rest (K₀) of collapsible loess is unable to reflect the influence of pressure and water content.In order to obtain the calculation method of K₀ under coupling conditions of pressure and moisture,experimental research of variation rules of K₀ during the wetting process for original loess was carried out.Firstly,a concept of wetting level was introduced to describe the moisture condition of soil.Secondly,stepped wetting tests were performed on loess under net vertical pressure to investigate the correlation between K₀ and the wetting level,matric suction,as well as vertical strain.Lastly,the conclusion of stepped wetting tests was verified through centrifugal model tests for the loess collapsibility.The experimental results showed that: 1) the concept of wetting level,reflecting the initial condition of moisture content and the process of wetting of loess,had a specific physical meaning;2) K₀ of original loess increased linearly with increasing wetting level.Additionally,the rate of increase of K₀ depended on the vertical pressure;the greater vertical pressure the slower the rate of increase;3) during the wetting process under different but constant vertical pressure,K₀ increased linearly with decreasing suction.However,the greater the vertical pressure the slower the rate of increase.The influence of matric suction on K₀ was similar to that of wetting level;4) data on ε(vertical strain) versus K₀ during wetting processes under different vertical pressures were distributed in a narrow range,which could be described using a hyperbolic curve.There was a small difference between the ε-K₀ curves of different pressure and water action sequences.On the basis of stepped wetting tests,an empirical formula for K₀ was established with the vertical pressure,wetting level and vertical strain as independent variables.