| It is one of important core research subjects in loess mechanics that the special sensitivity of collapsible loess to water. Understanding and reflecting the properties of deformation of increasing dampness correctly will has important values of theoretical guidance and practical application for engineering construction in loess district. Based on the present research results, a method to establish the constitutive law for collapsible deformation is proposed by studding the collapsible loess in Lanzhou.Started form the mechanism of collapsible deformation, the plastic property was analyzed according to the structural theory of collapsible deformation. Furthermore, the ZSM model is quoted in this paper, the mechanical model for collapsible deformation of loess was established. Through applying the conventional triaxial immersion tests, the properties of deformation of increasing dampness were studied, which was under different collapsible effects.In the paper, the moisture content of increasing dampness is regarded as an internal stress, and the collapsible volume yield surface and the shear yield surface are obtained through tests fit, and the method to determine the parameters in the yield functions is expounded in detail. The analytic expressions for initial collapsible stress and initial collapsible moisture content of collapsible loess are given through analyzing the stress -strain relationship curves of tests and combining the collapsible yield functions.Based on the generalized plastic theory, a constructive law with two yield surfaces for collapsible deformation of loess in this district is established. This model can reflect the major factors of influence on the collapsible deformation, and the relationship between collapsible volume deformation, collapsible shear deformation and collapsible deformation, and the coupling influence of spherical stress and deviator stress on the collapsibledeformation of loess.
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