Study on roof-cutting pressure relief technology for roadways with three-directional free surfaces and full anchor-cable support

Current studies on surrounding rock control in dynamic pressure roadways mainly focus on roadways under single- or two-directional free-surface conditions, while relatively few studies have applied the combined control technology of roof-cutting pressure relief and full anchor-cable support to dynamic pressure roadways with three-directional free surfaces. Taking the three-directional free-surface dynamic pressure roadway of the Ji15-23100 working face in Pingmei No. 4 Mine as the engineering background, the surrounding rock stress distribution characteristics before and after roof-cutting pressure relief were analyzed. The results showed that before excavation, the plastic zone of the three-directional free-surface dynamic pressure roadway had already exceeded the anchorage range of the original support system, and roof cutting could improve the surrounding rock stress environment and reduce the peak supporting stress. The original roadway support scheme suffered from insufficient support length and low pretension force, failing to effectively anchor the plastic zone, which resulted in large roof subsidence and severe sidewall damage in the three-directional free-surface dynamic pressure roadway. Based on the above analysis, a coordinated control technology of "roof-cutting pressure relief + full anchor-cable support" was proposed. High-strength anchor cables were used to form a superimposed beam structure to transfer roof loads to deep, stable rock strata, while roof-cutting blasting was employed to weaken key roof strata and interrupt stress transfer paths. Field monitoring results indicated that after implementing the proposed coordinated control technology, the maximum roof subsidence was reduced to 184 mm, and the maximum deformation of the coal pillar rib and solid coal rib reached 149 mm and 122 mm, respectively. These results verify the effectiveness of the proposed technology in controlling the surrounding rock of three-directional free-surface dynamic pressure roadways.