Search

In order to study the influence of drilling on the deformation and failure characteristics of coal, uniaxial compression tests were carried out for complete samples and briquette samples with drilled holes, and the strength characteristics, displacement field and crack evolution characteristics of the samples were analyzed. The results show that: under the same test conditions, compared with the intact sample, the uniaxial compressive strength of the sample with holes is reduced from 1.19 MPa to 0.95 MPa, and the reduction range is 20.17%; the failure modes of intact samples and samples with holes are tensile shear combined failure, and the failure shape of the samples with holes is “X” shape. Combined with the axial loading stress-time curve, the evolution process of the displacement around the holes of the samples with holes is divided into rapid growth, stable growth, slow growth. During the four stages of rapid growth, the displacement value of the measuring point increases with the increase of the horizon during the uniaxial loading process.

In order to study the dynamic evolution law of the pressure relief gas reservoir in the mining of extra-thick coal seams, the 3DEC numerical simulation software was used to analyze the stress and displacement distribution law of the overburden rock caused by mining, and the evolution characteristics of the pressure relief gas reservoir were studied, and the pressure relief gas was proposed. The method of discriminating the location of the reservoir area, and the practice of gas drainage in high-position boreholes at the test working face. The results show that: after the extra-thick coal seam is mined, the height of the overburden caving zone is 49.5 m, and the height of the fracture zone is 104 m. After the key strata in the pressure relief zone on the working face side loses stability, a pressure relief gas reservoir is formed below it. Pressure relief gas reservoir areas are divided into three categories: ①The key layer is in the bent subsidence zone, and the high-level reservoir is formed below it; ②The key layer is in the fracture zone, and the middle-level reservoir is formed under the masonry beam; ③The key layer is in the fracture zone. In the collapse zone, a low-level storage area is formed under the cantilever beam. The shape and area of ​​the reservoir are closely related to the state of the control key layer above. Before the control key layer is broken, the area continues to increase. The shape of the low-level reservoir is rectangular, and the shape of the middle and high-level reservoir is semi-elliptical, expanding to a three-dimensional shape. It is a rectangular cross-section ring body and an elliptical cross-section semi-ellipsoid body; the area decreases rapidly after breaking, and then changes periodically with the pressure of the overlying rock. The low-level reservoir is trapezoidal, the middle-level reservoir is triangular, and the high-level reservoir is shaped like a trapezoid. The shape is a semi-ellipse, and the three-dimensional shape is expanded to a rectangular cross-section ring, a triangular cross-section ring and an elliptical cross-section semi-ellipsoid. The location of the final hole of the high-level borehole was arranged in the range of the middle reservoir area, and the drainage verification was carried out. The maximum drainage concentration of a single hole was 34.5%, the average drainage concentration was 16.8%, and the upper corner gas concentration after drainage was 0.55%, The gas drainage effect is good, indicating that the arrangement of high-level drilling holes according to this method is reasonable.