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

Abstract EN

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.