Failure mechanism and divisional differentiated control of surrounding rock in mining roadway under remaining coal pillar in close‐distance coal seam

Abstract

AbstractRegarding the issue of intense mining pressure appearing in the underlying gateway below the remaining coal pillar in the close‐distance coal seam (the remaining coal pillar is perpendicular to the underlying section coal pillar), 401 working face is used as the engineering background. Field measurements, laboratory experiments, numerical simulations, and engineering verification techniques are used to study the abutment pressure's evolution properties and the plastic zone's propagation laws before and after the underlying coal seam roadway experienced the mining impact. The conclusions are as follows: ① The maximum plastic area on the two sides and the roof of the roadway underlying the gob are up to 2 and 1.5 m, whereas the maximum plastic area on the two sides and the roof of the roadway underlying the remaining coal pillar are up to 5 and 4.5 m, respectively. Moreover, the plastic area extends along the two sides, and the section coal pillar is completely broken when the working face is mined below the remaining coal pillar. ② The stress increase coefficient K in the overlap area of the remaining coal pillar and the underlying section coal pillar reaches 3.4 when the mining face penetrates the underlying remaining coal pillar and the advance abutment pressure is overlaid with the concentrated stress of the coal pillar. ③ When the underlying working face is mined to 4, −2, −8, and −14 m away from the remaining coal pillar, the damage range of the roadway 5–10 m ahead increases in turn. At the same time, the maximum plastic area of the roof passes through the plastic area of the upper coal seam floor. Therefore, the underlying and transition areas on both sides of the remaining coal pillar are divided into Area I (15 m) → Area II (the most complicated area to control under the remaining coal pillar, 20 m) → Area III (25 m) according to the width. Furthermore, the divisional differentiated combined control technology of channel steel truss anchor cable with joint double‐way locking control function of roof and coal pillar in Areas I and III, while channel steel truss anchor cable with joint double‐way locking control function of roof and side + high resistance integral door‐type support is proposed in Area II. Field engineering practice shows that the deformation of the roadway surrounding rock can be controlled within 210 mm after adopting the above divisional combined control technology. Finally, the mining operation can safely and efficiently pass through the remaining coal pillar. The research results have important reference values for surrounding rock control of mining roadways in the overlapping area of similar “+”‐type cross‐working face.