Determination of the stability of residual pillars in a room-and-pillar mining goaf under eccentric load

Abstract

In room-and-pillar mining (RPM), the roof of a coal seam is supported by coal pillars; however, the roof is non-uniformly deformed with time. Moreover, coal pillars at different positions are subjected to different stresses and some coal pillars are prone to the effects of eccentric load, thus influencing their stability. Therefore, by taking Bandingliang Coal Mine, Shaanxi Province, China, as the engineering background, the non-uniform deformation characteristics of the roof of a room-and-pillar mining goaf (RPMG) were first analysed by using numerical simulation and theoretical analysis. The residual pillars in the RPMG were partitioned into a uniform deformation zone, a transition zone, and a sub-uniform deformation zone; thereafter, the stress distribution in coal pillars under non-uniform deformation was revealed to show that coal pillars were subjected to non-uniform stresses; subsequently, the distributed force under the eccentric load was concentrated to attain the changes in stress state of coal pillars under eccentric load, including behaviour such as a non-uniformly compressed state, critical state, and a tensile stress state; finally, the pillar stability under the eccentric load was judged by taking the No. 19 coal pillar as an example. The result showed that the shear stress generated by the coal pillar was 0.58 MPa, which was lower than the allowable shear stress (1.51 MPa). As a result, the pillar did not collapse, consistent with actual conditions on site. The result is expected to provide a theoretical basis for controlling pillar stability in the RPMG. The theory of the stability of the residual pillars in the RPMG provided in this paper provides a new direction for determining the stability of pillars, and the study findings have been applied in specific mines and verified.