OPTIMIZATION TREATMENT OF INTAKE SLOPE AND TOWER FOUNDATION OF TUNNEL SPILLWAY FOR EXTRA-LARGE POWER STATION IN WEST MOUNTAIN CANYON AREA—TAKING CHANGHEBA HYDROPOWER STATION AS AN EXAMPLE

The mountain is high and steep in the western mountain canyon area. Even a very steep excavation slope ratio will produce a very high slope during slope excavation, resulting in difficult treatment and long construction period. Therefore, it is necessary to excavate as little as possible, carry out strong support in time, and achieve "high cleaning up, strong support, low opening and early entry" for the entrance of the spillway tunnel. In this way, the slope height of excavation can be greatly reduced, the construction difficulty can be reduced, the construction period can be reduced, and the investment can be saved. After the intake slope of the tunnel spillway was optimized, the tower foundation moved outward and was close to the slope surface. Attention should be paid to the unloading of rock mass and the adverse effects of unfavorable combination of structural planes on the slope below the tower foundation, stability analysis and calculation should be carried out, and support treatments should be taken when necessary. This paper summarized the successful treatment experience of flood discharge tunnel intake slope optimization and tower foundation slope in Changheba hydropower project on Dadu river, which can provide experience for other similar projects.