Bearing characteristics and parameter optimization of high-strength reticulated shell composite support for deep soft rock roadways

With the increase of coal mining depth, deep soft rock roadways are confronted with a complex environment characterized by "high erosion, high ground temperature, high osmotic pressure, high ground pressure, and strong disturbance". Severe surrounding rock deformation, floor heave, and large deformation of two sidewalls have become prominent issues. Traditional support structures are difficult to adapt due to defects such as easy deterioration of concrete and insufficient floor strength. To address this problem, this paper designs a composite support system of "high-strength steel mesh shell + shotcrete + bolt" and studies its bearing characteristics through numerical simulation and similar model tests. A three-dimensional numerical model was established based on ABAQUS, with the roadway of Dingji Coal Mine as the engineering background. The key parameters, including the burial depth of the high-strength reticulated shell floor, the diameter of longitudinal reinforcement, and concrete strength, were selected, and 16 groups of working conditions were designed using orthogonal tests. The results show that the influence degree of each parameter on the support effect is: burial depth > concrete strength > longitudinal reinforcement diameter. The optimal parameter combination is a burial depth of 1.0 m, a longitudinal reinforcement diameter of 12 mm, and concrete strength of C20, corresponding to the minimum floor heave of 14.32 mm. The surrounding rock of the roof and floor is mainly under compressive stress, with stress concentration at the foot of the sidewall. The reticulated shell steel bars mainly bear tensile stress, with a peak value of 48 MPa, forming a bearing system of "compression-based, tension-compression synergy". A physical model was constructed based on similarity theory, and a large-scale surrounding rock-support coupling test system was used to simulate the non-uniform stress field. The test shows that the instability of the support structure starts from stress concentration areas such as the foot of the sidewall and the shoulder, manifested as the expansion of local longitudinal cracks. The composite support structure can delay crack propagation through the synergistic effect between the latticed shell and concrete. In the similar model test, when the applied load stress reached 0.7 MPa, the stress at the arch foot increased from 4.4 MPa to 9.02 MPa, while the structure still maintained good integrity. This verifies the reliability of the numerical simulation results. The study confirms that the high-strength composite support structure can effectively improve the stability of deep soft rock roadways through parameter optimization, providing theoretical and technical support for support engineering under complex geological conditions.