DEEP FAULT ACTIVITY OF ESPECIALLY HIGH DAM FOUNDATION AND GEOLOGICAL ISSUES OF DAM ENGINEERING

This paper examines a planned hydropower station that is one of the important energy projects in overseas invested by China. It has a reservoir with high dam. Its water retaining structure is a roller-compacted concrete gravity dam of 200m high. The dam is located at a regional deep fault(F₄). Activities of fault and feasibility of damming technology, as an important technical issue, is key to the establishment of hydropower station. Thus, a lot of work, including regional seismic geological investigation, geophysical prospecting, drilling, exploratory adit, fault age, field and indoor tests for rock and soil physical and mechanical properties, has been conducted. Results show that:(1) Seismic activities in this fault are weak and the latest one is from 0.142 million to 0.798million years ago. The fault is inactive since late Pleistocene. (2) Cataclastic rock belt and the faults F_4-1 and F_4-2 have the most influence on the dam. The fresh cataclastic rock mainly is the Ⅲ_1B class rock. The Ⅳ_1B class rock only exists in F₄ footwall. Faults F_4-1 and F_4-2,which is composed of the Ⅴ class rock, have bad engineering properties, and are the most weak part of dam foundation; (3) The possibility of building the dam at fault F₄ to induce stereotype reservoir earthquake is less. The main engineering geological problem is deformation and seepage in dam foundation. Seepage stability can be dealt with through appropriate engineering measures such as deep digging and combining with backfilling concrete plug, consolidation grouting, deepening encryption and increasing the curtain row number. With results mentioned above all, an conclusion can be made that conducting hydropower projects on the fault F₄ zone is viable in technical way. The results can only provide technical basis for hydropower station design and construction, but also technical reference for similar projects.