The analytic solution for surrounding rock of roadway is of significance for stability analysis and roadway support. However, analytical solution for surrounding rock of roadway which took influences of water seepage, strain softening, dilatancy and intermediate principal stress all into account did not receive much reporting. To promote research in this aspect, a mechanical model simultaneously considering water seepage, strain softening, rock dilatancy, and intermediate principal stress was established based on porous elastoplastic mechanics, and then unified analytical solution for surrounding rock of roadway was obtained. Based on an example, influences of water seepage, strain softening, rock dilatancy, residual cohesion and intermediate principal stress on surrounding rock of roadway were thoroughly investigated using single factor analysis. The obtained results are as follows: radii of plastic zones and surface displacement of roadway would increase exponentially with water pressure increasing and their magnitudes are greater than corresponding values without water seepage considered; with softening modulus increasing, peak circumferential stress location would slightly shift to deeper surrounding rock, while broken zone radius and surface displacement of roadway would increase in a decay velocity; rock dilatancy has little effect on peak circumferential stress and plastic softening zone radius, while broken zone radius and surface displacement of roadway increase linearly with dilatancy coefficient α1 increasing indicating their magnitudes are overestimated if associated flow rule is adopted; with weighted coefficient increasing, stress components in plastic zones at the same distance from roadway center would increase, while radii of two plastic zones and surface displacement of roadway are reduced, i.e., self-bearing capacity of rock is enhanced considering intermediate principal stress effect compared to Mohr–Coulomb criterion; with residual cohesion increasing, peak circumferential stress remains unchanged, while stress components in plastic zones at the same distance from roadway center would increase and radii of two plastic zones decrease significantly. The above results implicated that water seepage effect should be carefully considered for roadway stability under groundwater environment; strain-softening and flow rule of rock should be reasonably analyzed and chosen to accurately predict surface displacement and broken zone radius of roadway; rock bolt length should be increased with softening modulus increasing, while it can be decreased with intermediate principal stress effect considered; grouting measure is an effective measure to improve roadway stability. In short, the research provides a theoretical basis and some practical engineering implication for roadway support.

Protective layer mining could not only significantly alter geostress but also increase the permeability of protected layer, which is beneficial for the coal gas extraction rate and ensures coal mining safety. However, due to unique geologic conditions, remote distance protective layer mining has its own characteristics. To investigate characteristic changes caused by remote distance protective layer mining, a suitable mathematical model that considered disturbance of unloading mining and solid-gas coupling effects during gas extraction was developed. The established mathematical model was implemented by combining FLAC3D and COMSOL programs to study characteristic changes during remote distance protective layer mining of Chajiaotan coal mine. Numerical simulation results of unloading disturbance mining indicated that the protected layer would experience a process of stress loading, stress unloading, stress recovery, and stress stability as the working face of protective layer advanced; unloading disturbance has a greater influence on coal permeability than gas pressure; gas extraction measure should be further adopted to decrease gas pressure. Numerical comparisons of gas pressure distribution in the original protected layer and unloading protected layer revealed that gas extraction after unloading disturbance can reduce gas pressure more effectively, and appropriate borehole spacings in the fully pressure-relief and nonfully pressure-relief zones are 30 m and 5 m, respectively. The layout of field boreholes for gas extraction was designed according to numerical results. The results of site investigation showed that numerical simulation results of relative expansion deformation and gas extraction radii agree well with the results of site observation, demonstrating reliability of the mathematical model and its implementation. The proposed mathematical model is promising for assessing unloading disturbance and gas extraction in remote distance protective layer mining.