Abstract:For supporting roof of underground powerhouse,a proper design of rock bolts should be based on a clear understanding of both formation and characteristics of the rock roof arch structure and the effect of rock bolt reinforcement. For this purpose,the mechanism of a rock cavern roof arch is studied and effects of different types of rock bolts are evaluated. Numerical modelling of rock bolt support of the Xiaolangdi powerhouse cavern is carried out and applications of arching theory are studied with the purpose to look into the effects of fully grouted rock bolts and tensioned cable anchors in reinforcing the cavern roof. It is concluded that a stable roof arch may be formed after excavation,systematic fully-grouted rock bolting is necessary in reinforcing the roof arch. However,the systematic tensioned cables should be used with caution since they may not be efficient after bolting,and further,they may create upward force to the arch,which counteracts the arch forming and possibly causes instability problems.