关键词: 软硬复合煤层, 瓦斯抽采钻孔, 软弱界面, 钻孔塌孔, 数值模拟

Abstract: In order to explore the deformation laws of gas drainage boreholes in soft and hard composite coal seams, the self-developed "a dynamic monitoring device for the stability of full-angle gas drainage boreholes" was used to conduct on-site monitoring. The system analyzed hard coal, soft coal, and soft coal. The deformation of gas drainage boreholes in hard composite coal seams, and the COMSOL numerical simulation method was used to verify the test results. The results show that the vertical strain sensitivity of the shallow part of the borehole lags behind that of the horizontal, and shows an alternating increase characteristic; Before the borehole strain attenuation stage, there is a short-term pseudo-equilibrium state, which is essentially the accumulation of internal stress in the coal body, which is then suddenly released to cause the borehole collapse; under the same external load conditions, the soft and hard interface will be a composite coal seam. Divided into two relatively independent stress environments, the coal seam has a sudden change of medium and a sudden change of stress at the weak interface; the deformation of each part of the hard coal seam is smaller than that of the soft coal seam, and both show large deformation in the shallow part and small deformation in the deep part. Finally, a stable hoop strain is achieved. The deformation of the perforation holes in the soft and hard composite coal seam in the shallow part is similar to the two. The deep part of the perforation holes and the weak interface cross and cut to form a stress concentration zone. The range of the stress concentration zone is along the weak interface and the borehole diameter. It extends at the same time and gradually attenuates. This attenuation presents an insignificant nonlinear characteristic.