Abstract：A brief introduction is given to the great challenge in the construction of Jinping I hydropower station，which is a key cascade underground hydropower project，located in the Southwest China，at the Yalong River. The challenge is caused by the following features. The project is very huge and the underground powerhouse system is very complicated，as well as the very high geostress and the complex geological conditions，including 3 large-scale faults and multiple sets of joints existing in the surrounding rock mass with poor quality combination. A detailed description is carried out to the extremely large deformations which is far beyond the deformation of other underground powerhouses with the same range of scale，and the time-related features of the deformation，the severe cracks of linings，the damaged zones develop continually，the over-loading of the rock- bolts and anchorages，during the excavation of the underground powerhouse caverns. All these phenomena happen frequently. Then，a preliminary analysis of those particular situations is given from the point of view of the relation of high stress level and the rheological feature of the rock mass. Finally，the feasibilities of several countermeasures are discussed，such as gradual support method，hierarchical controlling to the initial pre-stress of anchors，damage-zone consolidation and strengthening by the combination of bolting and grouting.
