Study on Deformation Characteristics and Failure Mechanism of Gas Extraction Hole Considering Strain Softening

ABSTRACT To better understand the strain‐softening effect and its implications for coal construction and extraction, this paper utilizes a numerical simulation method to investigate the deformation stability of gas extraction holes with consideration for strain softening. The study further analyzes the strain‐softening effect on effective stress, gas pressure, and plastic failure mode by comparing models with and without considering this effect. The results show that the plastic failure mode in the area close to the hole wall is mainly tensile shear combination failure. Shear failure occurs at the intersection angle of the X‐type shear zone and both the left and right sides, whereas tensile failure more likely occurs on the upper and lower sides due to shrinkage collapse. The displacement of coal increases with extraction time and stabilizes, along with the maximum effective stress concentration area and the plastic damage area. The strain softening process can negatively affect the extraction hole by increasing the displacement of coal, intensifying stress concentration, and exacerbating gas silting near the hole wall, ultimately hindering gas extraction efficiency. Also, faults and weak interbeds can further destabilize the extraction hole.