Study on in situ stress testing method based on Kaiser effect of acoustic emission and COMSOL simulation

In situ stress testing can improve the safety and efficiency of coal mining. Identifying the Kaiser effect point is vital for in situ stress calculations; however, the in situ stress calculation is limited by the rock sampling angle. Here, the Kaiser effect point identification theory is established and applied to the Xuyong Coal Mine. Uniaxial compression and acoustic emission experiments were carried out on sandstone with 6 sampling directions. Furthermore, COMSOL simulation is applied to study the in situ stress distribution in the coal mine to verify the calculation accuracy. The results are as follows. 1) The failure mode of non-bedded and vertical-bedded rocks is primarily tensile shear failure with obvious brittleness in mechanical and acoustic emission characteristics. Shear slip along the bedding plane is the primary failure mode of inclined-bedded rock. Additional take-off points exist in the AE count curve. 2) The Kaiser point identification method based on the variation of AE count curve parameters Δti and τi can effectively calculate the in situ stress. According to the numerical value of Kaiser point and sampling direction, the in situ stress of the conveyor roadway in the Xuyong Coal Mine was calculated as σ 1 = 22.81 MPa, σ 2 = 10.87 MPa and σ 3 = 6.14 MPa. 3) By the COMSOL simulation study, it was found that a stress concentration zone of 16.13 MPa exists near the two sides roadway. Compared with the Kaiser effect method, the deviation rates of the three-direction principal stress calculated by COMSOL were all less than 5%. This verifies that the in situ stress calculation by Kaiser effect in this study can be applied to the Xuyong Coal Mine.