Comparison of rockbolting in two underground powerhouses

Rockbolt reinforcement in the Xiaolangdi and Mingtan underground powerhouse caverns are compared with focus on the installation of tensioned cables used in stabilizing the roof arches. The Xiaolangdi Multipurpose Dam Project is located on the Yellow River, China and the Mingtan Pumped Storage Project in central Taiwan, China. The two machine hall caverns with arch shaped roofs have similar conditions in sizes, geological conditions and support design. However, the amount and length of tensioned cables installed are different. In both cases only small displacements were observed in the roof during benching. The response of the rock mass in the roof to the benching indicates that small stress changes are taking place, and that the roof arches are stable. Thus the additional tensioned long cables installed prior to benching may not have been necessary.