Development and application of a high-temperature and high-pressure true triaxial single-shear load transmission device for rocks

To elucidate the shear deformation and fracture behavior of rocks under the extreme conditions of deep engineering environments, an innovative true triaxial single-shear load transmission apparatus has been developed, accompanied by a corresponding method for true triaxial direct shear. This load transmission device is characterized by three key technologies: (1) A centrally symmetric double shear-double pressure interlocking load transmission structure has been engineered, overcoming the constraint of lateral stress/normal stress ≤ 1. This advancement allows for a more realistic and comprehensive restoration of the stress distribution state during the rock shear fracture process. (2) A hollow hydraulic self-balancing body has been designed, capable of withstanding oil pressures up to 70 MPa and temperatures of 150 ℃. This enhancement reduces the measurement error of shear strength by 52.7% to 75.4% compared to the previous silicone block approach, ensuring stability in load transmission at the flexible end of the shear component and guaranteeing the precise application and measurement of shear forces. (3) An embedded “sealant-cork layer-sealant” sandwich sealing configuration has been adopted, providing multiple layers of protection. This innovation marks a significant breakthrough in high-temperature and high-pressure true triaxial large displacement single-shear technology, accommodating shear displacement/specimen length ratios of up to 10%. High-temperature true triaxial single-shear experiments and acoustic emission monitoring were successfully conducted on granite specimens (50 mm×50 mm×50 mm). These experiments validate the reliability and expandability of the experimental setup. The apparatus features a straightforward structure with significant potential for widespread application, offering promising prospects for advancing studies on the shear mechanical properties of deep rock formations.