The effect of overlying rock fracture and stress path evolution in steeply dipping and large mining height stope

Abstract

Abstract To study the fracture instability characteristics and fracture mechanism of overlying strata in steeply dipping and large mining height stope, through the combination of physical simulation experiment, numerical calculation, theoretical analysis and field measurement, the correlation between the evolution of mining stress field and the fracture of overlying strata in large mining height stope under the effect of dip angle is analyzed, and the stress transfer path and the fracture mechanism of overlying strata are revealed. Finally, the influence mechanism of key strata on the evolution of the mining stress field of overlying strata is explained. The research shows that under the influence of gravity dip angle effect and mining height increase, the mining stress is non-equilibrium transferred and evolved in space, and the principal stress field presents the characteristics of partition evolution. The fracture trajectory of rock strata is multi-step and “八” shaped, and the inclined masonry structure and multi-step key strata form a cooperative bearing structure. The key layer of the ladder is the stress transmission structure between the caving zone and the stress arch, and the high stress in the overhanging area under the main roof is transmitted to the advanced roof. With the increase of dip angle, the height of the caving zone decreases, and the fracture range of ladder and principal stress arch decreases. The cracks in the middle and upper broken rock blocks increase, and the instability of the “high ladder rock layer” is easy to induce the simultaneous fracture of the “inclined masonry structure”, resulting in regional unbalanced instability and impact. The research results can provide some reference and guiding significance for the stability control of surrounding rock in longwall stope with steeply dipping.

Keywords

• Steeply dipping coal seam
• Large mining height
• Collaborative load-bearing structure
• Ladder key layer
• Fracture track line
• Gravity-dip effect