Experimental study on the static loading rate effects of sandstone specimen containing pre-existing echelon cracks

To investigate the static loading rate effects on the sandstone specimen with fissures,the mechanical proper-ty,failure mode,energy dissipation and acoustic emission (AE)response characteristics of sandstone specimen contai-ning pre-existing echelon cracks are tested in the laboratory under different loading rates. Based on the AE location technology and picture recording results,the evolution process of crack propagation and the loading rate mechanism are analyzed. The results show that:① There are significant static loading rate effects on sandstone specimen containing parallel echelon cracks under uniaxial compression. With the increase of loading rates, the uniaxial compressive strength,peak strain,initiation stress,the elastic energy at the peak stress and the peak AE counts gradually increase but the increase rate slows down. The elastic modulus shows the trend of first increasing and then decreasing. And the total number of accumulative AE counts shows a decreasing trend. ② The initiation of each new crack in the specimen corresponds to the stress drop in the stress-strain curve,the sudden rise of the dissipation energy and the high values re-sponse of the AE signals. ③ The specimens extend and slip along a pre-existing crack,and the shearing failure modes are formed at low loading rates. When the loading rates become larger,the final failure are tensile failure modes that the rock bridge between the two cracks links,and the outer edges of the pre-existing cracks extend to the upper and lower ends of the specimen along the loading direction. The results can provide a useful reference for further understanding on the mechanical response mechanism and revealing its evolution process of coal or rock dynamic disasters.