Based on the overburdened structure of shallow coal seams in the West of China, the traditional support resistance method may not apply in such regions due to many roof shear and support crushing accidents. Four support working resistance indexes—rated working resistance, average working resistance, average-partial working resistance, and average-upper working resistance are counted as the candidate working resistance. The method of optimizing and inverting working resistance was put forward based on the roof control effect and working resistance overrun percentage. The simulation of a fully-mechanized top coal caving working face was built by using the UDEC software to analyze the top coal cavability and roof subsidence under different supporting strengths to determine the final working resistance. The project practice of 1322 working face in Jindi coal mine shows that the working resistance is 80–90% of calculated rated working resistance. The hydraulic support is worked under good condition. There is no pillar shrinkage and support crushing during coal mining.

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.

Solid backfill mining as a green mining method has already been successfully applied in many mine sites. Higher requirements for the backfilling materials have been put forward in special regions, such as shallow coal seams, ecologically susceptible areas, and sites with building on the surface. The control effects of common backfilling materials on in situ strata of gob need to be studied and compared to ensure the suitable materials are applied in the mine. The meso-structure, stress variation, energy dissipation, and backfilling effects of the five common solid backfilling materials, which are Aeolian sand, gangue, mineral waste residue, coal ash, and loess are analyzed in this paper. The results show that the Aeolian sand and gangue are densely packed and internally hard when compared to other backfill materials. The deformation of the five materials to absorb the same amount of energy in the order of higher to lower was determined as Aeolian sand, gangue, mineral waste residue, coal ash and loess. The Aeolian sand’s strain energy density is 1.67 times larger than the loess, however, the Aeolian’s strain energy density in front of working face is just 32.2% of the loess, which is important to ensure the safety of the working face. The stress changes were monitored in situ with Aeolian sand and gangue as backfill materials. The monitoring results show that the Aeolian sand stress increase rate is quicker than gangue, which can support the roof effectively.

Pillar stability is an important factor for safe working and from an economic standpoint in underground mines. This paper discusses the effect of blast damage on the strength of hard rock pillars using numerical models through a parametric study. The results indicate that blast damage has a significant impact on the strength of pillars with larger width-to-height (W/H) ratios. The blast damage causes softening of the rock at the pillar boundaries leading to the yielding of the pillars in brittle fashion beyond the blast damage zones. The models show that the decrease in pillar strength as a consequence of blasting is inversely correlated with increasing pillar height at a constant W/H ratio. Inclined pillars are less susceptible to blast damage, and the damage on the inclined sides has a greater impact on pillar strength than on the normal sides. A methodology to analyze the blast damage on hard rock pillars using FLAC^3D is presented herein.