Failure analysis of a large span longwall drift under water-rich roofs and its control techniques

• The failure of a large span drift under water-rich roofs was analyzed by field investigations and numerical simulations.
• Numerical simulation results were compared with the field observations.
• Primary factors inducing the drift failure were determined.
• Control techniques were proposed to stabilize the large span longwall drift under water-rich roofs.

In this study, failure analysis of a large span longwall drift under water-rich roofs was presented relying on field observations and numerical simulations. We had sought to find the key points that caused the drift roof collapse and water inrush. The numerical results were similar with that observed from field situations, and they both determined the origins of the roof failure problem. Wrong location selection and unreasonable excavation and support schemes were verified to be the most important factors that caused roof failure of the drift. Subsequently, a new excavation location with poor roof aquifer was recommended. A two staged excavation procedure was employed. Firstly, a small span roadway was excavated and reinforced, then the roadway was widened to the design width. After the first pass, boreholes were drilled to dewater the roof aquifer, and chemical glue material was grouted into the roof to cement the pre-existing discontinuities and induced fractures. Such control techniques had been undertaken in the new longwall drift. Both numerical modeling and field measurement verified that the proposed method could guarantee the large span drift stability during excavation and longwall preparation period. The interest of this study resides in combining the integrated methods to evaluate the state of failure in a highly detailed manner and determine simultaneously control techniques for the thorny problem under study.