Creep and strength characteristics of post-peak stage loading in high strength red-sandstone

The post-peak stage-loading creep test was conducted on eight red-sandstone specimens by the RLW-2000 type servo rheometer system in the laboratory,the basic creep characteristics of post-peak red-sandstone was studied, the relationships of post-peak creep-failure strength and peak unloading strength,instantaneous strength were deter-mined,the internal mechanism of test creep curve and theoretical one was analyzed,the basic form of post-peak creep failure was discussed. The results showed that as stress level increased,post-peak instantaneous strain increased near-linearly. Instantaneous strain increased slightly with creep failure strength increasing at the same stress stage. As stress level increasing,creep strain increased as S type of decreasing-steady-increasing-rapid increasing trend,while non-at-tenuation creep occurred and creep strain increased obviously at last stress stage. As creep-failure strength increasing, creep strain decreased slightly at the same stress stage. Post-peak creep-failure strength was 84. 00% and 79. 92% of peak unloading strength and instantaneous one,respectively,and peak unloading strength was 95. 27% of instantaneous strength. Burgers rheological mode was better for fitting to the creep curve test,the relationship of creep test curve and theoretical one was larger at the high creep stress stage than the lower one. Specimen failure form showed the com-posite of main compression-shear failure surface and no-rule weaken zone,the lower creep-failure strength was,the lar-ger main failure angle and weaken zone,and the higher peak unloading value was,the more obvious main failure sur-face.