Mechanical Behavior of Shale at Different Strain Rates

The strain rate-dependent mechanical behavior of shale is characterized using triaxial compression tests under a constant confining pressure of 50 MPa and axial strain rates \(\dot{\varepsilon }_{1}\) ranging from 5 × 10−6 s−1 to 1 × 10−3 s−1. This study is conducted on the Longmaxi shale from Dayou in China, which is predominantly composed of brittle minerals including quartz (55%), albite (15%) and cristobalite (3%). The experimental results show that higher axial loading strain rates \(\dot{\varepsilon }_{1}\) lead to higher elastic modulus and higher peak shear strength, both following exponential relationships with \(\dot{\varepsilon }_{1}\). When \(\dot{\varepsilon }_{1} \le 1 \times 10^{ - 5} {\text{s}}^{ - 1}\), failure results in a single linear fracture, whereas a more complex multiple crisscrossing fracture network is formed when \(\dot{\varepsilon }_{1} \ge 1 \times 10^{ - 4} {\text{s}}^{ - 1}\). Failure in shale specimens can be described by a damage parameter \(D\), which is strongly affected by the axial strain \(\varepsilon_{{1{\text{s}}}}\). In addition, the strain rate \(\dot{\varepsilon }_{1}\) had different effects on \(D\), which also depends on axial strain \(\varepsilon_{{1{\text{s}}}}\). Energy accumulation and dissipation are also closely related to \(\dot{\varepsilon }_{1}\) with the total absorbed energy \(U_{\text{A}}\), the recoverable elastic strain energy \(U_{\text{A}}^{\text{e}}\) and the dissipated energy \(U_{\text{A}}^{\text{d}}\) at the peak stress increasing with \(\dot{\varepsilon }_{1}\). As for the total energy accumulation \(U_{\text{A}}\), the recoverable elastic energy \(U_{\text{A}}^{\text{e}}\) decreases while the dissipated energy \(U_{\text{A}}^{\text{d}}\) increases with increasing strain rate.