A shear constitutive model and experimental demonstration considering dual void portion and solid skeleton portion of rock

Shear deformation and break is a typical failure phenomenon of engineering rock. Building a constitutive model for rock shearing behaviors is a key issue in stability assessment of geotechnical engineering. A dual-structure shear constitutive model was developed to reveal the full shearing deformation evolution features of geological material. It was assumed that the rock was composed of void portion and solid skeleton portion. Thus, the macro constitutive relation of rock shearing deformation was established by accumulating the micro voids’ shear deformation and solid skeleton deformation. The comparison analysis of four geological materials indicated that the constitutive model can fully characterize the shear deformation and failure evolution process of rock, including the compaction stage, linear elasticity, shear hardening, shear softening, bimodal phenomenon and residual stages. At the micro level, the damage variable (D) evolution of solid skeleton can be divided into three stages: (i) pre-damage stage; (ii) accelerated damage deterioration stage; and (iii) completed damage stage. It was worth paying attention to the Weibull parameters (m, u0), where parameter m reflected the brittle failure characteristics of the rock, and parameter u0 indicated shear peak strain and peak strength of rock. Finally, physical shear experiments for cemented paste backfill-rock were carried out and the bimodal shear failure mechanism was comprehensively analyzed based on the proposed constitutive model.