Stability Control of a Roadway Surrounding Rock during the Cutting and Pressure Relief of a Coal-Bearing Roof at a Shallow Mining Depth

Abstract

Recent years have seen the widespread use of a new gob-side entry retaining technology, namely, automatic roadway forming based on roof cutting and pressure relief. However, because of the complex geological conditions, stability control methods for the surrounding rock remain unexplored. In this paper, through theoretical analysis, field measurement, and numerical simulation, the stability control of a roadway surrounding rock under roof-cutting and pressure-relief conditions is studied. The key stage in the steady-state control of this type of rock is determined by establishing a mechanical model of the hard roof in the process of automatic roadway formation. The results show that the roof-cutting and pressure-relief technology outperforms the conventional mining technology in terms of surface crack development and subsidence. The roadway roof movement can be divided into three stages: a direct roof-caving activity period, a basic roof-breaking activity period, and a roof-stabilizing period. The stress above the original roadway is gradually transferred to the adjacent working face, and a stress concentration is formed on the working face 6 m away from the roadway retaining section. In this scenario, the roadway is in a stress-reducing area, which ensures its safety. Based on the research results, we suggest adding a constant resistance and large deformation anchor cable near the cutting seam side for active support. A single-hydraulic prop + I-beam + steel mesh can support the working face, and a grouting bolt support can help reinforce the broken and loose surrounding rocks at the gangue-retaining side of the roadway. Thus, the movement of the surrounding rock can be effectively controlled. An industrial test shows that the effect of retaining roadway is evidently improved.

Key parameters of gob-side entry retaining by roof cutting in close-distance seam group

“…The core idea of gob-side entry retaining by roof cutting is to replace the coal pillar with a collapse gangue [19][20][21]. Directional presplitting is used to blast the roof strata of the roadway before mining [22,23].…”

Hydraulic fracturing method for relieving stress concentration in remaining coal pillar in overlying goaf

“…To solve the problem of large deformation of the roadway in the lower seam, the method of increasing the width of the sectional protection coal pillar is generally adopted, and the roadway in the lower level coal seam is arranged below the overlying goaf 1 . Strengthening roadway support can also be used to reduce the deformation of the roadway, 2,3 such as using a combined support process of the bolt, anchor, steel shed, and single hydraulic props. However, increasing the width of the sectional protection coal pillar will result in a waste of coal resources; once the width of the coal pillar is left unfavorable, it can also cause instability of the coal pillar group, posing a great safety hazard 4 .…”

Numerical Study on Failure Mechanisms of Deep Roadway Sidewalls with Different Height-Width Ratios and Lateral Pressures

“…This capability supports the investigation of parameter sensitivity and aids engineers in optimizing design schemes for underground engineering. The stress and strain in the surrounding rock after excavation are analyzed to determine the damage state of the roadway [9][10][11][12].…”