The stability and roof-support optimization of roadways passing through unfavorable geological bodies using advanced detection and monitoring methods, among others, in the Sanmenxia Bauxite Mine in China’s Henan Province

The safety and stability of roadways is greatly influenced by the complex geological conditions present in the Sanmenxia Bauxite Mine, Henan Province, China. In this study, based on data from field survey, advanced detection methods, numerical studies, and monitoring studies, we have adopted the method of steel fiber-reinforced shotcrete to improve the excavation rate of roadways and guarantee the safety of the tunnel when it passes through unfavorable geological bodies, such as shale rocks and broken argillaceous limestone. Field surveys showed that the stability of roof rocks is the major problem faced by engineers; however, tunnel construction using cast-in-situ concrete, which is the method currently applied, costs too much time, resulting in an excavation rate that is too slow to meet the requirements of the Sanmenxia Bauxite Mine. Here, we propose an optimized scheme which, when combined with numerical simulations and data from advanced detection techniques and field monitoring surveys, can improve the efficiency of roadway roof support. During the implementation of the new scheme, the geological anomalies ahead of the working face were detected in advance. It is assumed that the supporting effect of the steel fiber-reinforced shotcrete is equivalent to that of the cast-in-situ concrete as long as a certain thickness is reached. Moreover, the steel fiber-reinforced shotcrete has better mechanical properties than cast-in-situ concrete and achieves a better combination effect with surrounding rock masses. Based on geological conditions and numerical results, the shotcrete should be thickest in the middle area along the roadway axis passing through the unfavorable geological bodies, and gradually become less thick from the middle to both ends. Field tests were carried out to verify the effectiveness of the scheme. The monitoring results show that the roadway passing through broken argillaceous limestone was stable after being supported by shotcrete (at least 80 mm); its thickness should reach at least about 120 mm when passing through shale rock mass. The results indicate that the use of steel fiber-reinforced shotcrete can considerably shorten the construction time compared with cast-in-situ concrete support. The scheme has proved to be a feasible, economical, and time-saving method for underground excavation in the Sanmenxia Bauxite Mine.