Development of a 3D loading sealing device and simulation test of coal thickness variation zone outburst

At present,the complexity of geotechnical engineering problems is still difficult to be satisfactorily solved by theoretical research or numerical simulation methods. Physical model tests offer a more effective solution to these issues. Extensive research has been conducted on physical model tests and three-dimensional hydraulic loading devices. In response to that small-size devices are difficult to consider and involve the influence of geological structural factors,as well as the difficulty in sealing the box of large-sized three-dimensional hydraulic loading devices,a large-scale true three-dimensional hydraulic loading sealing test device was independently developed. The counter force frame of the device is 4 300 mm×3 580 mm×3 150 mm(length×width×height),and the test loading box has overall dimensions of 2 050 mm×1 400 mm×1 300 mm(length×width×height). This box is a three-way true triaxial loading sealed box capable of conducting true triaxial loading tests on coal and rock samples under 10 MPa in-situ stress and 3 MPa high-pressure gas conditions. Simultaneously,a similar simulation test of coal and gas outbursts during tunneling in the area of coal seam thickness variation was conducted using a dedicated test platform,and the change rules of gas pressure,coal rock stress and temperature were studied. During gas charging, the coal adsorbs gas and releases heat,leading to a rise in temperature within the coal seam. Before the outburst, the stress value in the coal thickness variation area is large. At the moment of the outburst,the high-speed gas flow of the outburst carries the broken coal and rocks out,and the gas pressure near the outburst point drops rapidly. After the outburst,the gas desorption and external expansion work make the temperature in the coal seam drop. The temperature change near the structural belt in the coal thickness variation area is the most significant,the maximum drop can reach 7.3 ℃. The stress at the coal rock interface of the top and bottom plates decreases sharply at the same time. The coal thickness variation area produces a high stress concentration,and the stress value has a short rise process,with the maximum value reaching 1.4 MPa. The mass ratio of coal powder is 34.75%. Finally,based on the experimental results,the energy analysis of the outburst process in the coal thickness variation zone was carried out. The experimental results comply with the energy instability criterion for coal and gas outburst,and the disturbance caused by external forces on coal can directly or indirectly induce the occurrence of coal and gas outburst. © 2024 Academia Sinica. All rights reserved.