Determining loose zone range and optimizing borehole sealing depth in Tianchi coal mine

The determination of loose zone in coal roadways is the key to determining the initial sealing depth of gas drainage boreholes and ensuring the sealing quality. In view of the high gas concentration in Tianchi Coal Mine, the distribution characteristics and influencing factors of the loose zone in the coal roadway were systematically analyzed by combining numerical simulation and on-site measurement. Firstly, on-site samples were collected to measure the mechanical parameters of coal and rock. The numerical model of the coal roadway was established using COMSOL Multiphysics simulation software to simulate the stress changes and the distribution of plastic zone after the excavation of the coal roadway. Then, the loose zone of the coal roadway at the test working face was measured on-site using the cuttings quantity method. Based on the dynamic changes of the cuttings output per meter during different drilling construction processes, and by integrating the results of numerical simulation and on-site tests, the range of the loose zone of the coal roadway at the test working face was determined. Finally, analyze the influence characteristics of the cross-sectional size and burial depth of the roadway on the range of the loose zone, and determine the reasonable sealing depth. The results show that the plastic zone of the surrounding rock of the roadway is distributed in a butterfly shape. The range of the loose zone in the coal roadway of the test working face is 8 meters. When the cross-sectional radius of the roadway increased from 2.6 meters to 3.6 meters, the range of the loose zone nearly doubled. When the burial depth of the roadway increased from 400 meters to 700 meters, the range of the loose zone expanded from 5 meters to 12 meters. In light of the actual situation of the test mine, it is recommended that the initial sealing depth be set at a position greater than 8 meters during the drilling and sealing operation to enhance the effect of gas prevention and control. The research results provide theoretical basis and practical reference for the design of sealing depth in high-gas mines.