A method for evaluating the stability of roadway surrounding rock based on a modified damage evolution characteristic model considering rock mass residual strength and 3D DEM

Repetitive mining in multi-seam conditions induces cumulative damage to surrounding rock, significantly increasing the risk of roadway instability. Taking the roadway in the extra-thick coal seam fully mechanized top-coal caving face as the research object, this study innovatively developed a modified damage evolution characteristic model that considers the residual strength of rock mass to quantify the regulatory effect of damage variable D on roof fracture span: damage to the main roof reduces the initial and periodic fracture spans, significantly increasing the probability of slippage and rotational instability of the voussoir beam structure. On this basis, a three-dimensional discrete element method (3D DEM) model was established, and orthogonal tests were designed to reveal the coupling mechanism of the spatial position of fracture lines and coal pillar width on rock mass damage. The results show that when the coal pillar width increases from 8 m to 16 m, the peak stress at the roadway ribs decreases by 26.5%–43.3%, and the influence range of the second invariant of the deviatoric stress tensor ( J 2 ) shrinks. The attenuation of stress gradient leads to a decrease in the evolution rate of plastic damage with increasing coal pillar width, while the position of the fracture line has a weak regulatory effect on the stress-plastic response of the coal pillar. The results of theoretical analysis and 3D DEM simulations have effectively guided on-site engineering practice. • Proposed a modified damage evolution characteristic model considering rock residual strength properties. • Clarified the evolution process of interlayer main roof from gradient damage to through-going instability. • Revealed the coupling mechanism between coal pillar and fracture line via 3D DEM orthogonal tests. • A synergistic support system of high-strength prestressed long-short bolts and cables effectively ensures roadway stability.