Abstract: A stability study is conducted for the top-arch collapse composite treatments of the Dagangshan Hydropower Station, based on a sophisticated analysis approach of the composite linings. The performance of the treatments during excavation is analyzed. The internal forces of the I-beams and the shorcrete are presented respectively for the distinct phases of treatment. In this manner, the stability of the treatments are discussed. The results indicate that the maximum incremental displacement after treatment is about 9 cm. Fail zones of the top-arch remain broadly unchanged afterwards. The changes of the cables’ internal force are relatively small, suggesting a good supporting efficiency and safety level. Although the initial treatments may suffer potential cracking, as the main components of the treatments, the phaseⅠand phaseⅡ treatments are in a good state. Therefore the stability of the entire treatment system may be insured. Monitored data are generally agree well with the calculated ones; the analysis reliably reflect the real rock mass deformation and the internal forces state of the supporting structures.

Key words: underground powerhouse, collapse, composite lining, support capacity, stability analysis