Influence of bedding angles on dynamic properties of Yanchang shale and a DIF-based constitutive model

As global conventional natural gas resources are increasingly depleted, shale gas, a key form of unconventional natural gas, has gained significant attention due to advancements in extraction technologies. This study investigated shale samples from the Yanchang Formation of the Ordos Basin. Mechanical tests were conducted on shale specimens with bedding orientations of 0°, 45°, and 90°, including static tests (uniaxial compression, triaxial compression, Brazilian splitting) and dynamic impact tests (SHPB), facilitating a comprehensive analysis of strength, deformation, and failure modes under various loading conditions. The results indicate pronounced anisotropy in shale's mechanical behavior. Dynamic compressive strength increases with strain rate, exhibiting a distinct U-shaped relationship with bedding angle. Based on experimental data, an enhanced HJC constitutive model is proposed, replacing the conventional strain rate term with a dynamic increase factor (DIF). This modification significantly improves predictions of material behavior under high-strain-rate loading. Moreover, the refined HJC model outperforms both the RHT and HJC models in characterizing shale behavior under high-strain-rate conditions. The findings provide essential mechanical parameters and a robust constitutive framework to support efficient and environmentally sustainable shale gas extraction.