Dynamic tensile failure of layered sorptive rocks: Shale and coal

Shale and coal samples were selected to clarify the tensile failure of layered sorptive rocks under the co-influence of bedding planes and loading conditions. Results indicate that, for these two rocks, tensile strength exhibited anisotropy. As loading rates rises, inverted Trumpet-shaped trend lines is proposed to reflect bedding effects with loading effects. The tensile strength of shale increases linearly with the bedding angle rises, while the value of coal shows great dispersion. The former is greater than the latter. An ultimate loading rate exists for shale and coal. Empirical relations were established to describe tensile strength with varying loading rate and bedding angle. Under the co-influences of bedding plane and loading conditions, more complex failure modes happened for coal and shale samples. Hydraulic fracturing along the direction of 60° (for shale reservoirs) or 45° (for coal reservoirs) to the bedding plane is more likely to produce a complex fracture network.