Abstract:

There were a large number of deep fractures within the slope of the Baihetan hydropower station dam area，which was neither tectonic origin nor different from conventional unloading fractures，the formation mechanism of such special geological phenomena and their impact on engineering construction of hydropower stations had become a problem that needed to solve. The characteristics and distribution pattern of deep fractures was summarized on the basis of detailed description of deep fractures and the formation mechanism was analyzed by combining with tectonic evolution, valley evolution of canyon and the theory of near surface action and by the result of in situ stress testing and dating, using the mechanism analysis of geological processes. The results show that the deep fractures is epigenetic structure with NW and NE orientation, tensile characteristics, concentration distribution,location above the dislocation belt and is in the stress fluctuation zone of slope. The primary reason of deep fractures formation is strain energy release and residual tensile stress caused by difference resilience. Formation age of deep fractures is after Ⅲ terraces appearance,namely Late Qp₂-Early Qp stages.

Key words: Baihetan hydropower station, deep fractures, near surface action, strain energy, formation mechanism