Rock support design based on the concept of pressure arch

A metal mine stope, located at a depth of about 1000 m below the surface, experienced drastic changes in roof displacement and wall fracturing within a short period of time. Thus, the stope needed additional reinforcement in order to remove the remaining ore. It was revealed from rock mechanics assessment that the stability problem was owing to the relatively low strength of the rock as well as the high in situ stresses. It was believed that both the roof and the hanging wall were heavily fractured. It was then proposed that the unstable section of the stope be reinforced with bolt–shotcrete ribs. The concept of the design was to form a pressure arch in the failed rock with the help of six bolt–shotcrete ribs. Displacement measurements showed that the roof displacement reduced from about 2 mm/day to a level of about 0.25 mm/day immediately after the reinforcement operation. Two hanging wall collapses occurred a few months later in the areas outside the bolt–shotcrete reinforced section in the stope. The collapses indirectly proved the effectiveness of the bolt–shotcrete ribs in reinforcing the failed rock.