Experimental study on mechanical properties of Beishan granite in the mild temperature range

Abstract

The response of mechanical property to temperature, especially in the mild temperature range, is important for the high-level waste (HLW) geological disposal engineering. To study the temperature effect on the deformation properties and the mobilization of strength of Beishan granite, the incremental cyclic loading-unloading compressive tests under various temperatures (T) and confining pressure (σ3) conditions (T = 25 °C, 60 °C and 90 °C, σ3 = 0 MPa, 5 MPa and 20 MPa) were carried out on Beishan granite. Results showed: (1) During the entire compression process, the cohesive strength is weakening while the frictional strength is strengthening. The CWFS model was developed considering the temperature effect. (2) For the peak strength, the cohesion decreased while the friction increased with increasing temperature in the range of 25 °C–90 °C. (3) The mechanism of cohesion weakening and friction strengthening with increasing temperature was discussed based on the micro-structure measurement. Clear thermal induced crack/pore closure was observed in granite after mild temperature treated, which contributes to friction strengthening and stiffness improvement. (4) The strength response to temperature (cohesion weakening and friction strengthening with increasing temperature) will result in ‘transition pressure (10.1 MPa for crack damage stress, and 14.9 MPa for peak strength)’ for Beishan granite under mild temperature that the surrounding granite would be strengthened by the elevated temperature under higher confining pressure. The transition pressure is important for high-level waste geological disposal engineering in repository layout design optimization.

Keywords

• Beishan granite
• Mechanical property
• Mild temperature range
• High-level radioactive waste disposal
• Transition confining pressure