Co-effects of bedding planes and loading condition on Mode-I fracture toughness of anisotropic rocks

Abstract

The mechanical and fracture behavior of rocks are mainly determined by the discontinuous defects inside the rock and the external force state. The focus of this research is to clarify the co-effects of bedding planes and loading conditions on the fracture behavior of anisotropic rocks. Notched semi-circular bend (NSCB) tests are performed on anisotropic rocks with varied bedding angles (from 0° to 90°) and loading conditions (from static loading to impact loading). By analyzing the failure characteriacs recorded throught the experiments and fracture toughness of anisotropic rocks (shale and coal), a critical loading rate, two failure modes, three empirical relations, upper and lower envelopes are provided. In addition, bedding effects, laoding rates effects and co-effects between them are further investigated. The experimental results indicate that the bedding effects is the most obvious under static loading and becomes weaker as loading rates increase. At this time, the loading rates effects plays a dominant role. Under the co-effects of bedding plane and loading conditions, the failure modes become more complex and the fracture toughness exhibits inconsistent characteristics for anisotropic shale and coal. Due to the different internal discontinuities, the maximum loading rate that shale and coal can withstand differs greatly, which further affects their mechanical and failure behaviors. The results have sightful implications to the response of anisotropic rocks to engineering activities.