Investigation on support pattern of a coal mine roadway within soft rocks - a case study

Supporting coal mine roadway within soft rocks is a typical challenge in underground mining practices. As the most widely used support structure, rock bolt system has been successfully used to support coal mine roadways in various complex geological and geotechnical conditions, including roadway in extremely weak rock masses, roadways 1000 m below ground, open-off cut roadways with large section, and roadways along the edges of mined-out areas with thin pillars or even no pillars. However, the effectiveness and applicability of rock bolt system for the reinforcement of soft rock masses has not yet been established. In this paper, we present a case study of rock bolt system as used for ground reinforcement of longwall entries within soft rock masses. The study site was the tailgate of the longwall panel 5-2S at the Hongmiao coal mine in the Pingzhuang coal-mining district in China, a typical soft rock coal mine of the region. Since traditional rock bolt system failed to maintain the stability of the tailgate, the effectiveness of rock bolt systems for this application remained doubtful. The reasons for the failure of the rock bolt system were first examined. A discrete element method simulation was then performed to better understand the mechanism of rock bolts in supporting soft rocks. An improved rock bolt system was finally proposed that was used to support the tailgate. The field monitor showed that the improved rock bolt system successfully suppressed cracking and dilation of the tailgate. This case study is useful in enhancing engineering applications of rock bolts to support longwall entries excavated in soft rock masses.