The damage of brittle rock is induced by its microcrack growth which significantly affects the deformation and strength of rocks subjected to the compressive loadings. However

the relationships between microcrack growth and the variable shear properties（cohesion

internal friction angle

and shear stress） are rarely studied. In this study

the relationships between internal friction angle

cohesion

shear strength and micro-parameters at the peak point of stress-strain relationship are proposed

according to the stress-strain relationship triggered by crack growth and the Mohr-Coulomb failure criterion. By introducing the Mohr-Coulomb yield criterion

the theoretical expression is established for dynamic variations of cohesion

internal friction angle and shear stress along with microcrack growth or strain at plastic deformation phase of brittle rocks. Cohesion

internal friction angle

and shear stress firstly increase until to maximum values

and then decrease with the increasing crack growth or axial strain in brittle rocks under compressive loading

which is corresponding to the stress-strain constitutive curves in triaxial compressive tests. Finally

the rationality of the proposed theoretical expression is verified by comparing with the experimental results. Besides

the effects of friction coefficient between microcrack interfaces on the relationships between cohesion

internal friction angle

shear stress and crack growth or axial strain are discussed.