Brazilian disc test study on tensile strength-weakening effect of high pre-loaded red sandstone under dynamic disturbance

Tensile failure (spalling or slabbing) often occurs on the sidewall of deep tunnel, which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance. To reveal the mechanism of rock tensile failure caused by this coupled stress mode, the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic disturbance. Based on the pure static tensile fracture load of red sandstone specimen, two static load levels (80% and 90% of the pure static tensile fracture load) were selected as the initial high pre-static loading state, and then the dynamic disturbance load was applied until the rock specimen was destroyed. The dynamic disturbance loading mode adopted a sinusoidal wave (sine-wave) load, and the loading wave amplitude was 20% and 10% of the pure static tensile fracture load, respectively. The dynamic disturbance frequencies were set to 1, 10, 20, 30, 40, and 50 Hz. The results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load, and both parameters decrease significantly with the increase of dynamic disturbance frequency. With the increase of dynamic disturbance frequency, the decrease range of tensile strength of red sandstone increased from 3.3% to 9.4% when the pre-static load level is 80%. While when the pre-static load level is 90%, the decrease range will increase from 7.4% to 11.6%. This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic disturbance. In this tensile failure mechanism of the deep surrounding rock, the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure, the pre-static load level dominates the tensile failure strength of surrounding rock, and dynamic disturbance promotes the strength-weakening effect and affects the weakening range.