Study on pressure relief effect of upper protective coal seam mining based on distributed optical fiber sensing monitoring

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On site real-time monitoring of protective layer mining is an important method to deeply study its pressure relief mechanism. It is proposed that the distributed optical fiber sensing technology (BOTDA) based on Brillouin optical time domain analysis is used to conduct mining industry tests on the deformation law and pressure relief effect of the underlying coal and rock mass during the mining of the upper protective layer. Taking the 21,104 comprehensive mechanized working face of Hulusu Coal Mine as an example, the strain transmission relationship between the coal and rock mass and the force-bearing optical fiber sensor is analyzed, and the design scheme, implantation scheme and installation process of the optical fiber sensor monitoring system are introduced. Implemented the accuracy analysis of the optical fiber sensing monitoring system and the spatial positioning of the sensors. According to the mining progress of the working face, the optical fiber sensing monitoring system regularly collects data, and by analyzing the strain distribution characteristics of the sensing optical cable and its dynamic change process, the deformation law of the underlying coal and rock mass in the mining of the upper protective layer is obtained. The monitoring results show that the underlying coal and rock mass undergoes a dynamic process of compressive strain increase, tensile strain increase and tensile strain recovery during the mining of the upper protective layer, and the scale of increase and decrease of strain of coal and rock mass at different depths are different; The intensity of coal rock deformation and pressure relief effect are characterized by the fluctuation amplitude of optical fiber strain increment. The pressure relief process can be divided into three stages: the pressure relief start stage is 40.8 m, the pressure relief active stage is 68.3 m, and the pressure relief decline stage; Finally, the strike pressure relief angle of the upper protective layer mining is 58.7°, the inclined pressure relief angle is 63.6°, the pressure relief lag distance is 14.2 m, and the maximum vertical distance of pressure relief is 28.4 m. The research shows that the application of BOTDA distributed optical fiber sensing technology in monitoring the pressure relief effect of protective layer mining can provide a reliable basis for coal mine safety mining.