2-D FEM parametric numerical analysis of inclined coal pillars

Pillars are used as the primary support structures for underground mining to maintain stability by supporting the over laying strata. In the case of horizontal seams, the pillars are typically subjected to axial loading due to the weight of the overburden and/or abutment stresses, while in the case of inclined seams they are subjected to oblique loading due to both the vertical and horizontal in-situ stress. Over the years numerous studies have been completed on square and rectangular pillars in horizontal seams that have resulted in several pillar stability equations and criteria. However very few studies are available with respect to pillars in inclined seams. Inclined pillars are subject not only to high normal stresses, but they are also subject to higher shear stresses that depend on the inclination of the seam, the ratio of the horizontal to vertical in-situ stress as well as the physical and mechanical properties of the material. This paper presents a parametric numerical investigation of pillars in inclined seams using the finite element method by evaluating different geometrical parameters such as seam inclination, as well as different pillar strength parameters. It is concluded that under elastoplastic conditions, high shear stresses are developed at the pillar-roof interface for inclined pillars and such stresses increase as pillar inclination increases. Shear stresses for elastic models are higher at the rib locations. Shear stresses are slightly higher on the downhill side of inclined pillars than on the uphill side. Finally, the major principal stresses at the rib are higher for the elastic models than the elastoplastic models.