Laboratory and field investigations of different bolting configurations for coal mine roadways in weak coal strata

The underground mining roadways are composed of different strata in southern China mining areas. In the rock-coal composite roadways (RCCRs), surrounding rock comprises coal seam and other strata, such as sandstone, mudstone and siltstone. In this paper, a systematic laboratory experimental study was carried out in which uniaxial compressive strength test was used to investigate the reinforcement of fabricated rock-coal composite (RCC) specimens possessing different anchoring (bolting) setups: no bolt, one horizontal bolt in the coal, two horizontal bolts in the coal and one horizontal bolt in the coal together with an inclined bolt crossing the coal-rock interface. The results show that the failure of RCC specimens with no bolts initially occurs in the coal. Bolting improves the mechanical behaviour of the RCC specimens and the level of improvement is related to the number and orientation of the bolts. Using one horizontal bolt in the coal together with a 30° inclined bolt crossing the coal-rock interface results in the highest strength and the most effective reduction of differential deformation of the RCC specimens. Based on the experimental laboratory results, a field study was carried out to demonstrate further the effectiveness of the inclined bolting and anchoring crossing the coal-rock interface in the stress compression zone for restraining the uneven deformation of the RCCR.