Influence of Mining Parameters on the Distribution Law of Separation Layer and Water-Flowing Fracture in Mining Overburden

Abstract

The internal overburden movement after coal mining may cause many disasters to the on-site production. It is of great guiding significance for the engineering treatment such as separation layer grouting and gas extraction to master the evolution law of separation layer and fracture in the overburden. Combined with the full-columnar overburden of a certain working face, this study established a number of models using 3DEC simulation software and analyzed the influence of different mining heights and widths on the distribution law of separation layer and fracture after strata movement. The simulation results show that the evolution of separation layer in the overburden after mining roughly consists of three stages, namely, initial generation, reaching peak, and tending to close (stable). The development of the separation layer is positively correlated with the mining height and negatively correlated with the mining width. When the mining height increases from 3 m to 5 m, the peak value of cumulative separation increases from 0.7 m to 2.1 m. On the contrary, when the mining width increases from 250 m to 350 m, the peak value of cumulative separation decreases from 2.8 m to 1.1 m. The pre-bearing stress concentration will be formed in the mining process of the working face. The influence of mining width change on the peak of stress concentration is greater than that of mining height change, and the subsidence is mainly affected by mining height. A quantitative analysis method of water-flowing fracture development height was developed by using the penetration height of joint shear displacement. The calculated fracture zone height 117.33 m was in good agreement with the actual measured results 120 m, verifying the validity of this method. These findings are of great reference for mastering the distribution law of separation layer and fracture in the mining overburden.

Experimental study on rock strata movement and stope stress distribution law under mining height regulation

“…Similar conclusions were also made in the literatures. 24,25 According to the geological conditions of the working face, the optimal mining height can be selected. It can make the distribution range of the caving zone, fracture zone, and bending subsidence zone reach the optimal combination, so that the pressure relief effect is the best.…”

“…The main methods used are numerical simulation, theoretical analysis, and mathematical statistics. In terms of numerical simulation, Tang et al 22 studied the regional variation characteristics of abutment pressure in front of coalface under different mining depths and thicknesses in the Lianghuai mining area; Zhu et al 23 analyzed the stress in the region of coal seam thickness change, drew the energy distribution map in the region of coal thickness change by numerical simulation, and proposed the rock burst control measures; Xie et al 24,25 simulated and analyzed the influence of different mining heights and widths on the distribution law of separated strata and fracture after strata movement; Li et al 26 analyzed the characteristics of coal wall of large mining height coalface under different mining heights through FLAC 3D simulation; and Chen et al 27 studied the effect of different thicknesses of mined coal seams on the deformation degree of the floor. In terms of theoretical analysis, Xie et al 28 established a viscoelastic damage model of abutment pressure distribution and analyzed the abutment pressure distribution of solid coal in front and side of coal wall at different mining heights; Liang et al 29 proposed that there are two structural forms and six movement forms in the key strata of the large-height mining face with large mining height by theoretical analysis method; and Zhao et al 30 created a fractal dimension model and analyzed the fractal characteristics of overlying strata at different mining heights.…”