Design of multi-layer coupling support and span of setup entry roof at depth

Abstract

The setup entry is driven at the starting line of a longwall panel and used to set up equipment, from which mining activities begin. The roof stability of setup entry roof with large span is a major concern in deep underground coal mines, especially when the surrounding strata are weak and fractured. Large-span setup entry roofs at depth induce a serious danger of roof fall and difficulty in the determination of the rational span. We determined a reasonable span for such a situation by studying the 1105 large mining-height coal face setup entry of Zhaogu No. 2 coal mine. A multi-layer coupling support method, led by long-extension bolt and medium length cable, was proposed. The setup entry was designed for four layers of coupling support. The setup entry’s reasonable span was determined and the reliability of the coupling support system was analyzed. These measurements allowed us to set up separate roof depth-displacement monitors and bolt (cable)-condition sensors in the mined area and enabled us to remove secondary instrumentation. The monitoring results show that unstable setup entry roof collapse occurs as roof-fractionated instantaneous fracture within 0 to 6–10 m. The size of the hanging roof varies between 11.7 and 13.6 m at the first fracture, and the hanging roof varies between 13.0 and 14.0 m at the time of the second fracture. For complete roof instability, the reasonable span should be ~ 12.4 m. The deformation of each horizon’s roof and the roof fall achieve effective control in the anchorage range before roof fracture, and the support effect of the core level is significant with a long-extension bolt (20-mm diameter × 5000 mm) and cable (21.6-mm diameter × 12,000 mm). The roof’s rupture depth did not develop further, which indicates that the multi-layer coupling support can adapt to control the large-span roof of setup entry at depth.