Laboratory and Numerical Investigation on Strength Performance of Inclined Pillars

Abstract

Pillars play a critical role in an underground mine, as an inadequate pillar design could lead to pillar failure, which may result in catastrophic damage, while an over-designed pillar would lead to ore loss, causing economic loss. Pillar design is dictated by the inclination of the ore body. Depending on the orientation of the pillars, loading can be axial (compression) in horizontal pillars and oblique (compression as well as shear loading) in inclined pillars. Empirical and numerical approaches are the two most commonly used methods for pillar design. Current empirical approaches are mostly based on horizontal pillars, and the inclination of the pillars in the dataset is not taken into consideration. Laboratory and numerical studies were conducted with different width-to-height ratios and at different inclinations to understand the reduction in strength due to inclined loading and to observe the failure mechanisms. The specimens’ strength reduced consistently over all the width-to-height ratios at a given inclination. The strength reduction factors for gypsum were found to be 0.78 and 0.56, and for sandstone were 0.71 and 0.43 at 10° and 20° inclinations, respectively. The strength reduction factors from numerical models were found to be 0.94 for 10° inclination, 0.87 for 20° inclination, 0.78 for 30° inclination, and 0.67 for 40° inclination, and a fitting equation was proposed for the strength reduction factor with respect to inclination. The achieved results could be used at preliminary design stages and can be verified during real mining practice.

Experimental study on granite acoustic emission and micro-fracture behavior with combined compression and shear loading: phenomenon and mechanism

“…Previous reports undermined the UCS of rock material as these are dependent upon external loading 16,26,27 . In general, UCS is the primary reference index employed for pillar strength designs based on experimental tests performed under pure uniaxial compression conditions.…”

“…Pariseau 14 and Foroughi 15 previously reported the effect of the external shear loading on coal pillar stability estimation in inclined coal seams. Jessu 16 indicated the dependence of the pillar design on the inclination of ore body. Specifically, the pillar orientation exhibited axial loading (pure compression) when using horizontal pillars and oblique loading (combined compression-shear loading) when using inclined pillars.…”

Timber props standing support structures as replacement of extracted pillars in an inclined Airleg stope

“…They neglect the influence of pillar inclination on the rule of loading variation from normal to tilted loading. This tilted loading mechanism initiates a combination of compression and shear loads on the pillar's boundary [6,26,27]. Jessu and Spearing [4][5][6] confirmed this by conducting a FLAC 3D numerical analysis to evaluate the inclined pillar's strength and failure mechanism.…”

Theoretical Analysis for Stability Evaluation of Rock Mass Engineering Structure under Combined Compression-Shear Loading: A Case Study of Inclined Pillar

“…According to the compression-shear loading characteristics o the inclined pillar, the combined compression-shear loading test is proposed to stud the mechanical behavior of the inclined pillar. Jessu et al [21] conducted compression shear tests on gypsum and sandstone pillar samples with diameters of 50 mm and dif ferent width-to-height ratios in the laboratory and studied the deformation and strengt characteristics of inclined pillar samples. The results showed that pillar strength de creased with the increase of dip angle.…”