| The article elucidated the regional geo-environment and engineering geological conditions of the hydraulic tunnel. Firstly and the rockmass quality of the surrounding rock is appraised. In this foundation, the stability of the tunnel before and after support is analysed. The prediction of large deformation is made at last. The research results mainly include as follows:(1) Based on the detailed illustration of regional environment engineering conditions, taking the engineering geological condition difference as the basic principle, the engineering geological subdivision is made reasonably and the geological condition of each segment is appraised.(2) In the foundation of summarizing the surrounding rock classification, Combined with the character of gaopingpu hydraulic tunnel, the surrounding rock classification is made reasonably adopting the method of surrounding rock engineering geological classification recommended by《Code for water resources and hydropower engineering geological investigation》(GB50287-99).(3) Stability analysis for the surrounding rock of typical section plane in each engineering geology section and deep lying section adoping separately the two-dimensional numerical modeling and the three-dimensional numerical modeling. The results indicate that the surrounding rock of the hydraulic tunnel appcars the varying degree stress distribution newly, the displacement is bigger, plastic failure area distribution is larger. After the shotcrete-bolt support, the displacement of the surrounding rock is minished greatly, the plastic failure area scope also obviously reduces, the surrounding rock of the tunnel is at the steady state on the whole.(4) The prediction of large deformation in the tunnel has been given by using of geological and complex predicting method and tangential strain method. The result is that the problem of large deformation in gaopingpu hydraulic tunnel maybe will occur in the position where deep ditch locates and deep lying section in the tunnel.
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