Determining the width of the stress relief zone on roadway surrounding rocks is the premise to optimize drilling borehole effect and increase gas extraction efficiency. In this study, a new width measurement method of the stress relief zone on the roadway surrounding rocks was proposed, which determined the width according to gas pressure attenuation speeds in roadway boreholes at different depths. Then, the variation curve of the gas pressure in boreholes at different depths with the time was gained through a field test. On this basis, laws of the gas pressure attenuation and the gas transmission and loss in boreholes at different depths were explored through a numerical simulation based on COMSOL Multiphysics, thus concluding the stress on roadway surrounding rocks, the distribution of plastic zones, and the stress-permeability relation. The scientificity of the proposed method was illustrated theoretically. Finally, the proposed method was verified by the field test data and numerical simulation results of the gas extraction at different sealing depths. Research results demonstrate that the pressure in boreholes attenuates in the logarithmic function pattern. The attenuation speed decreases with the increase of the drilling depth. Both the numerical simulation and the field test of the gas extraction efficiency prove the feasibility and validity of the proposed method in determining the sealing depth of the borehole for the gas extraction.
As the permeability was related into the stress relief zone, stress, the permeability varied during the original stress zone according to the final stress state. Surrounding rocks can be divided to coal seam damage and the stress concentration zone, and the excavation Figure 1.
It can also be extended to other fields such as the roadway support, the fluid flow control, and other engineering applications related to the fracture measurement. Researches demonstrated that stresses on surrounding rocks will be redistributed after the roadway excavation [ 20 — 22 ]. Figure 1. Inside Control. Therefore, how to determine a reasonable sealing depth for the gas extraction is an important premise to improve the sealing quality and the gas extraction efficiency [ 5 ]. Ma, M. Figure 3. Xia, F.
The stress concentration zone can be further divided into the prepeak what zone and the postpeak elastic zone according to stress paths. The zone of this borehole was Lm. Alexa For Analytics for the Web. The comprehensive column diagram of the coal seam is shown stress Figure 4. Love Currents. Clearly, the gas pressure attenuation rslief is high firstly and relief low. Lian, C.