Numerical simulation of damage-seepage evolution of tunnel coal-rock under excavation disturbance

Abstract The coal-rock of the coal tunnel will be damaged and the permeability will be changed under the action of excavation. To explore the change law of coal-rock stress, damage and permeability ahead of the working face of coal tunnels under excavation disturbances, this research establishes a seepage-stress-damage (SSD) model. Using COMSOL and MATLAB software, simulations are conducted to analyze the variation in coal-rock damage, stress, and permeability under varying excavation step lengths, coal-rock homogeneity, and tunnel burial depths. The results show that as the working face advances, the vertical stress in the coal seam and surrounding rock increases, leading to expanded damage zones and enhanced permeability at monitoring points. With increasing homogeneity, localized vertical stress in the surrounding rock intensifies, while the damage zones in both coal and surrounding rock progressively reduce. Additionally, a lower homogeneity coefficient in surrounding rock corresponds to higher coal permeability. With the increase of overburden load, the peak stress of surrounding rock gradually increases, which causes the damage area of coal seam and surrounding rock to increase. And the increase of overburden load leads to the corresponding increase of coal permeability. When the borehole spacing is 2 m and the extraction time reaches 90 d, the comprehensive effect of gas extraction is the most suitable.