STUDY ON GEODYNAMICAL PROCESS AND EVOLUTION MECHANISM OF DEEP-INCISED RIVER VALLEY SLOPE OF XIAOWAN HYDROPOWER STATION

Xiaowan hydropower station locates in the mountain-gorge region,the geodynamical process of the deep-incised river valley decides its present morphological characteristics,rock mass structure and stability,and deeply effects slope design plan and selection of dam base surface.Based on field investigation and experimental analysis,these main conclusions are formed as follows: (1)The exogenetic reconstruction of deep-incised valley slope is very strong because of unloading and weathering effect,and a great number of middle-gentle fissures are generated,the SN high dip angle fissures near slope surface are propagated and gapping; and a great number of EW compressed zone(surface)generated near the slope surface.(2)the generation mechanism of middle-gentle fissures includes propagation of old joint and new generation,the middle-gentle fissures in river valley bottom are further propagated because of differential unloading rebound,and when rock mass quality in the upper slope is stepwise lowering and so earth stresses are stepwise adjusted,the middle-gentle fissures are propagated because of shear slide,the river valley slope stepwise enter time-effect deformation period; (3)The geo-engineering classification of river valley slope is proposed,the potential deformation failure modes of each classification are topping failure,plane slide,steplike slide,wedge failure and accumulation body faiure etc.