Strength properties of shale samples of layered structure under shear loading with coupled compression

The research was performed of strength properties and failure mechanism of shale samples of layered structure under shear loading with coupled compression. The effect of angles of orientations of stratification planes Ψ and angles of shear plane Δ on ultimate shear strength of shale specimens was analyzed. The results indicate that ultimate shear strength depends on combination of values of bedding angle and angle of shear plane relative to the stratification. The empirical dependences of the cohesion on angles Ψ and Δ were obtained. Minimum and maximum values of cohesion have been defined depending on values of angles Ψ and Δ. The combinations of angles Ψ and Δ are determined that are most dangerous for shear fracture of rocks of layered structure.