Study of structural effect on mechanical properties and failure characters of layered rocks

Layered sandstone, coal, shale and other layered rocks are widely distributed in coal mine strata. The layered rock is an anisotropic rock with the same mechanical properties along the layer and various mechanical properties in the perpendicular direction. The different combinations of matrix and layers lead to the structural effects, such as size effect, as well as bedding density and inclination angle effect, which would affect the strength and failure characteristics of layered rocks. For the influence of structural effect on the mechanical properties and failure characteristics of layered rocks, the size effect, as well as bedding density and inclination angle effect were analyzed. The influence of structural effect on stress-strain curve characteristics, peak strength, deformation characteristics and failure characteristics was studied. The results were as follows. Both the peak strength and elastic modulus decrease with the ratio of height to width. The size effect is weakened by the confining pressure. Under the triaxial state, the structural unstability is weakened, and the ductile characters become obvious. The peak strength and elastic modulus of the layered rock mass at the inclination angle 90° approach the maximum. The confining pressure and layer inclination would affect the brittle-ductile transition characteristics, damage degree and failure form. The results could provide important theoretical basis for the calibration of mechanical parameters and analysis of failure mechanism in layered surrounding rocks in deep mining.