Principle and technology of in-situ magnetically controlled multidirectional pressure-preserved coring in the coal mine

Obtaining the in-situ physical and mechanical parameters of coal-rock mass is the primary task for the development of deep coal resource. Accurate measurement of the in-situ parameters of gas is the basic guarantee to realize the safe mining of coal. In view of the technical challenges of inaccurate measurement of in-situ gas parameters in coal mine, the idea of multi-directional pressure-preserved coring technology based on magnetic force control was proposed with consideration to the technical characteristics of coring in underground coal mines. Specifically, a self-triggered magnetically controlled pressure-preserved controller was designed based on the characteristics of the composite magnetic field. The triggering and sealing structure for coring was optimized. The key pressure-preserved components realized the non-contact self-triggering and self-sealing by magnetic force control, thus improving the fault tolerance of the pressure-preserved trigger. Besides, a test platform functioning for multi-directional pressure-preserved coring was developed independently. With the self-developed test platform, it was verified that the pressure-preserved controller had a good triggering and self-sealing ability at different coring angles. In addition, a magnetically controlled pressure-preserved module was integrated to form a multidirectional pressure-preserved coring device. Moreover, laboratory tests were conducted to verify that the device could realize the pressure-preserved coring in multiple directions, and the pressure-preserved capacity could reach 6 MPa, which meets the condition of pressure-preserved coring in coal mines. The research results provide technical support for the multidirectional pressure-preserved coring in deep coal mines and provide a new idea for the design of pressure-preserved control structure.