Slate with inherently transverse isotropy is abundant in metamorphic rock, in buildings, and in geotechnical engineering worldwide; the tensile and shear fracture behavior of layered slate is vital to know for engineering applications. In this paper, the Brazilian and semi-circular bend (SCB) tests of layered slate were performed. The fracture characteristics of the slate were investigated by numerical simulations developed by the hybrid finite and cohesive element method (FCEM). Results showed that the measured experimental tensile strength, and mode I fracture toughness of layered slate all showed a typical V-type trend as the bedding angle increased from 0° to 90°, and with divider type. The developed empirical relationship between tensile fracture toughness and tensile strength K_IC = 0.094σ_t + 0.036 fitted experimentally and strongly correlated. The mechanical response and fracture patterns predicted by FCEM agreed well with those of the laboratory experiments. Moreover, the shear fracture behavior and mode II fracture toughness of the layered slate were explored by systematic numerical simulations. Research results provide potential insights for further prediction and improvement of the complex fracture behavior of anisotropic rock masses for rock engineering.

The transverse isotropy of rock masses formed by sedimentation is a common stratum environment in engineering, and the physical–mechanical properties can degrade due to water–rock interaction (WRI) and natural weathering, which potentially lead to the instability or collapse of tunneling, slopes and mining. Taking the carbonaceous slate of the Muzhailing tunnel as the research object, two types of specimens, which include oven-drying (instant drying in oven after fabrication) and natural air-drying (static weathering for 60 days after fabrication) were prepared, respectively, after which Brazilian tests were carried out and the tensile properties were analyzed under the two conditions. The experimental results showed that the two kinds of carbonaceous slate all show brittle failure, but the mechanical response such as failure displacement and peak load is obviously different. The tensile strength of the specimens is significantly all affected by the bedding, while the cleavage failure patterns of the two kinds are affected to different degrees. The softening coefficient of the natural air-drying specimen is 0.11–0.13, which implies that WRI and natural weathering play a vital role in the course of rock failure but have little influence on the transverse isotropy tensile property of bedding. Moreover, the mechanisms of specimen failure subject to WRI and 60 days’ weathering were explained by the SEM technique, which analyzed the micro-components and observes the process of specimen deterioration due to physicochemical reaction, the gradual development of cracks and erosion by weathering.