Abstract:The mechanical and hydraulic properties as well as the coupled hydromechanical(HM) behaviours of fractured rock mass are mainly controlled by its geological discontinuities. The deformation,fluid flow and coupled HM mechanisms of discontinuities are key scientific issues for multi-field coupling analysis. From the viewpoint of coupled HM analysis,the discontinuities are characterized as an interfacial layer. The geometrical and mechanical properties of the interfacial layer are described by apertures,stiffness coefficients or Lame constants. The closure behaviour,shear dilation and contraction,and coupled HM process of the interfacial layer under normal load or combined normal and shear loads are investigated. Deformation models are established to characterize the elastic,elastoplastic and post-peak responses of the interfacial layer. Based on these,a generalized cubic law and an analytical unsaturated flow model are proposed by considering the coupled HM effects. The proposed deformation models,flow models and coupled HM models based on the concept of the interfacial layer are validated by experimental tests;and the model parameters can be determined by simple experimental tests. With the interfacial layer model,the deformation analysis and the flow analysis of discontinuities and rock masses can be performed on the basis of the same physical model. As a result,the coupled HM mechanism of rock masses can be better understood;and the reliability of multi-field coupling analysis can be improved. Moreover,the interfacial layer model can be applied to the coupled HM analysis not only for the discrete media but also for the equivalent continua.