Research on Mechanical Properties of U-Shaped Retractable Gangue Prevention Structure of Gob-Side Entry by Roof Cutting and Pressure Releasing in Deep Mining

Abstract

In recent years, as a new type of gob-side entry retaining method, roadway automatically formed by roof cutting and pressure releasing (RAFRCPR) has been widely used in China. Under the condition of deep mining, the deformation of the gangue rib of the automatically formed gob-side entry retaining is difficult to control, and it is difficult for the traditional I-shaped steel to provide the needed support. To effectively control the deformation of the gangue rib, a new type of U-shaped retractable gangue prevention structure (URGPS) with high lateral support strength and axial compressible dynamic absorption energy is proposed. Based on the geological conditions of the 21304-working face in the Chengjiao coal mine in Henan, the mechanical characteristics of URGPS and the causes of its local instability are analyzed in detail employing theoretical analysis, laboratory tests, and numerical simulation. A reasonable bolt tightening force, overlap length, and lap combination form of the URGPS are determined according to the actual situation of the project site. Engineering practice shows that a URGPS that was applied to control the deformation of the gangue rib in deep roof-cutting roadway was effective.

Study on the gas outburst control effect of goaf on the neighboring working face: Case study of Pingmei No.4 Mine

“…1. Upper boundary condition: In general, the upper boundary condition of numerical calculation is set as the weight of the overlying rock layer on the coal seam [25][26][27] :…”

“…The boundary conditions are set as follows: Upper boundary condition : In general, the upper boundary condition of numerical calculation is set as the weight of the overlying rock layer on the coal seam 25–27 : $$$\sigma =\gamma H,$$$where $$\gamma $$ is the average unit weight of the overlying rock layer on the working face, 2.4 t/m 3 ; H is the working face burial depth, H = 945 m. Then, there is $$\sigma $$ = 22.5 MPa. Bottom boundary condition : Due to the small impact of the 31040 working face on the floor rock layer, and it not being considered as a research object, the model bottom plate is simplified as a fixed constraint, with a displacement of 0. …”

“…Upper boundary condition : In general, the upper boundary condition of numerical calculation is set as the weight of the overlying rock layer on the coal seam 25–27 : $$$\sigma =\gamma H,$$$where $$\gamma $$ is the average unit weight of the overlying rock layer on the working face, 2.4 t/m 3 ; H is the working face burial depth, H = 945 m. Then, there is $$\sigma $$ = 22.5 MPa.…”

Study of the Internal Rebreaking Characteristics of Crushed Gangue in Mine Goaf during Compression

“…Under the action of a certain stress level, the particles in the crushed gangue sample move and slide, which changes its spatial arrangement and pore distribution. Because the cylinder used in the test had a large stiffness, the radial deformation of crushed particles was not considered in the loading process [50]. According to fractal theory in gangue crushing, the total mass of the crushed gangue is set as M t , where the mass of particles smaller than the particle size di is M 1 (d i ), and the mass of particles larger than the particle size d i is M 2 (d i ), where…”

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

“…The technology of gob-side entry retaining by roof cutting solves the problem of the stress concentration of the back ll, and the construction process is simpler [7][8][9]. To date, this method has been successfully applied under a variety of working conditions such as thin coal seams, thick coal seams, hard roofs, composite roofs, shallow burials, and high gas mines and has achieved good economic bene ts [10][11][12].…”