Abstract: During the measurement of gas pressure in borehole embedded in coal seam, drilling deformation and collapse are very difficult to avoid. In order to fundamentally seal the cracks around borehole in coal seam, gas pressure measurement method conducted in borehole embedded in imitative rock has been put forward in this paper. The mechanical analysis of drilling instability shows that the radius of drilling fracture zone is relevant to rock lithology. Improving the internal friction angle and the cohesion of surrounding rock is an effective way to enhance the strength of rock. Moreover, through mechanism analysis of solidified borehole in coal seam and numerical simulation, it has been found that high pressure grouting technique applied to coal seam can strengthen the intensity of borehole surface. Field comparison tests show that the difference between gas pressure measured in imitative rock borehole and rock borehole is 0.02 MPa and its relative error is only 3.85%. Consequently, gas pressure measurement method in imitative rock borehole is feasible and has a promising future.

Key words: gas pressure measurement, instability, fracture zone, high pressure grouting, imitative rock borehole