Stability Analysis and Derived Control Measures for Rock Surrounding a Roadway in a Lower Coal Seam under Concentrated Stress of a Coal Pillar

Abstract

Numerical simulations have often been used in close-distance coal seam studies. However, numerical simulations can contain certain subjective and objective limitations, such as high randomness and excessively simplified models. In this study, close-distance coal seams were mechanically modeled based on the half-plane theory. An analytical solution of the floor stress distribution was derived and visualized using Mathematica software. The principal stress difference was regarded as a stability criterion for the rock surrounding the roadway. Then, the evolution laws of the floor principal stress difference under different factors that influence stability were further examined. Finally, stability control measures for the rock surrounding the roadway in the lower coal seam were proposed. The results indicated the following: (1) The principal stress difference of the floor considers the centerline of the upper coal pillar as a symmetry axis and transmits radially downward. The principal stress difference in the rock surrounding the roadway gradually decreases as the distance from the upper coal pillar increases and can be ranked in the following order: left rib > roof > right rib. (2) The minimum principal stress difference zones are located at the center of the left and right “spirals,” which are obliquely below the edge of the upper coal pillar. This is an ideal position for the lower coal seam roadway. (3) The shallowness of the roadway, a small stress concentration coefficient, high level of coal cohesion, large coal internal friction angle, and appropriate lengthening of the working face of the upper coal seam are conducive to the stability of the lower coal seam roadway. (4) Through bolt (cable) support, borehole pressure relief, and pregrouting measures, the roof-to-floor and rib-to-rib convergence of the 13313 return airway is significantly reduced, and the stability of the rock surrounding the roadway is substantially improved. This research provides a theoretical basis and field experience for stabilizing the lower coal seam roadways in close-distance coal seams.

A Study on the Impact of Longwall‐Mining Operation on the Stability of a Slope‐Pillar Structure

“…In the simulation test, when the width of the protective pillar was below 20 cm, the instability of the slope body tended to occur, with the crack surface as the boundary and the inner side of the pillar (close to the working face) as the supporting point to facilitate the process of sliding and rotation. During the movement, the hinged pieces experienced instability and sliding, resulting in the "sliding rotation load" transferred from the back side of the strata to the pillar, which led the load to the inner side of the pillar and dynamic mining pressure [22].…”

Research on the evolution of the deviatoric stress and control of a gas extraction roadway under mining influence

“…Many experts and scholars at home and abroad have studied and analyzed the failure characteristics and instability mechanism of the surrounding rock under the influence of mining from different angles. Based on halfplane theory, Sun et al(2020) modeled close-distance coal seams, regarded the principal stress difference as a stability criterion for the rock surrounding the roadway, and put forward stability control measures for the roadway surrounding rock in the lower coal seam. In order to solve the problems of roadway stability and easy instability under repeated mining of close-distance coal seam groups, Xiong et al(2021) studied the mechanism and control technology of surrounding rock instability under repeated mining via physical similarity simulation experiment.…”

Study on stress evolution law and control technology of roadway formed by roof cutting during crossing overlying remained coal pillar

“…And many studies on the reasonable layout of roadways have been carried out to determine the location of roadways under the influence of ORCP (Liu et al, 2016; Wu et al, 2018; Yan et al, 2015). Besides, in order to determinate the control measures of surrounding rock stability, it is necessary to study the stress distribution characteristics of ORCP and the optimal coal pillar size (Gao et al, 2019; Sun et al, 2020a). However, the traditional long-wall mining mode not only cannot completely relief the relationship between the excavation and mining fundamentally, but also cannot increase the mining rate in the mining process of close distance coal seams.…”