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.
Highlights
Introduction rough nearly60 years of exploration and practice, the gobside entry retaining (GER) technology has achieved good results in applications, is a relatively complete coal-pillarfree mining technology [1–5], and has promoted the development of coal-pillar-free mining
In the study of GER supports, various safety factors, support principles, and support methods have been proposed depending on the geological conditions through theoretical derivation, physical simulation, numerical simulation, and field monitoring [6, 7]. rough a computer simulation analysis of a roadway bolt support design, a sensitivity analysis method for the roadway support safety factor has been proposed [8,9]. e bolt strength, bolt shotcrete thickness, and lithology significantly influence the GER effect [10]
In the GER approach, the roadway-side support controls the basic roof of the roadway, and the control of the roof inclination serves as a theoretical basis for designing the working resistance and shrinkage of the roadside support [14, 15]. e roof activity law in different periods has a varying influence on retaining the roadway, and the mechanism of roadway-side reinforcement support can be explained through mechanical derivation
Summary
An adequate height is required for roof cutting to ensure that the movement of the rock beam on the main roof of the overlying strata in the goaf is supported by the caving gangue. Based on previous research and based on the analysis of key parameters of automatic roadway with RCPR, the influence of height and angle of roof cutting on the strata behaviors had been simulated and studied with the FLAC3D numerical simulation software, which confirmed that the optimal roof cutting height and splitting angle of the 12201 working face of Halagou Coal mine were 6 m, respectively. Since the coal seam of the 12201 fully mechanized face had a composite roof, the roof-cutting height was set as 6 m. E bilateral cumulative tensile explosion was employed for directional roof cutting. In this approach, two shaped charges were placed in a gathering device with two preset blasting directions. Ground Pressure Behavior Law of RoofCutting and Pressure-Relief Stope with Three Shallow-Buried Composite Roofs
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