Abstract:
To address the problems of excessive labor demand, high labor intensity, low efficiency, and low drivage rate associated with U-shaped steel supports in coal roadways, the structural optimization of a combined active and passive support system for roadways in "three-soft" coal seams was investigated. A "U-shaped steel + anchor cable" combined active and passive support design scheme was proposed. Based on the original U-shaped steel (passive support), anchor cables (active support) were added. The U-shaped steel was used to provide surface support for the shallow surrounding rock, while the anchor cables were used to reinforce the deep surrounding rock mass. ABAQUS software was used to simulate the deformation characteristics of the U-shaped steel supports. The results showed that the support instability modes mainly included four types: peaked-roof failure, concave-roof failure, roof shrinkage failure, and leg buckling failure. Based on the simulation results, theoretical calculations, and field investigations, the positions for supplementary anchor cable installation in the U-shaped steel were determined. The critical load-bearing capacities of U-shaped steel supports with defects under four typical loading conditions were simulated. Compared with the intact support, the critical loads under the four typical loading conditions decreased by 40%, 34%, 30%, and 46%, respectively. Concrete was filled into the opening of the U-shaped steel, and the critical load of the defective specimen increased by 902 kN, showing a significant reinforcement effect. The influence of different support spacings on roadway surrounding rock deformation under combined active and passive support conditions was analyzed. The results indicated that a support spacing of 600–800 mm could effectively control surrounding rock deformation. Field monitoring was conducted on roof separation and roadway surface displacement. The results showed that, after optimization of the combined active and passive support structure, good roadway support performance was achieved.