Energy dissipation characteristics of sandstone under triaxial extension with different confining pressures
摘要
After excavation, some of the surrounding rock mass is in a state of triaxial extension, exhibiting tensile or shear fracture modes. To study the energy mechanism of tensile fracture turning to shear fracture, a series of triaxial extension tests were conducted on sandstone under confining pressures of 10, 30, 50 and 70 MPa. Elastic energy and dissipated energy were separated by single unloading, the input energy ut, elastic energy ue, and dissipated energy ud at different unloading stress levels were calculated by the integrating stress – strain curves. The results show that tensile cracks dominate fracture under lower confining pressure (10 MPa), and shear cracks play an increasingly important role in fracture as confining pressure increases (30, 50 and 70 MPa). Based on the phenomenon that ue and ud increase linearly with increasing ut, a possible energy distribution mechanism of fracture mode transition under triaxial extension was proposed. In addition, it was found that peak energy storage capacity is more sensitive to confining pressure compared to elastic energy conversion capacity.