By establishing a normal deformation model for rock joints subjected to normal and shear loading with consideration of post-peak dilatancy and shear softening

a generalized cubic law is proposed on the basis of the equivalence principle of seepage flow dissipation energy for better describing the irreducible seepage flow behavior for the joints subjected to large normal closure and the post-peak seepage flow behavior at the presence of dilatancy and shear softening. The proposed theory has been validated by an existing coupled shear-flow test

showing that the seepage flow behavioral trend of rock joints in post-peak stage can be enough accurately predicted by the traditional cubic law penalized with a small constant.