EXOGENETIC RECONSTRUCTION CHARACTERISTICS AND MECHANISM OF LOWER ELEVATION BANK SLOPE AT DAM SITE OF XIAOWAN HYDROPOWER STATION

The geo-characteristics of the lower elevation bank slope of Xiaowan Hydrostation were systematically and widely observed at the foundation of dam, the slope of water-cushion pond and lower elevation drainage galleries. Based on field investigation and 2D finite element analysis of elasticity and plasticity, the exogenetic reconstruction characteristics of lower elevation bank slope were more understood. (1) Its development was based on the reconstruction of rock association and structure, including the stretch and slippage of old gentle joints, the stretch and slippage of deep joints and their changing of occurrence, the new generation of a great number of middle-gentle cracks, the weaker and weaker exogenetic reconstruction inwards. (2) The generation mechanism and model of gentle cracks triggering from exogenetic reconstruction in lower elevation was established, and the formation process was analysed. (3) During the 2D finite element analysis of elasticity and plasticity, the slack boundary due to unloading in lower elevation was studied on the basis of the indexes of tensilely destroyed zone distribution, shearing strain and point safety degree. As a result, the obvious depth affected by exogenetic reconstruction on the bottom of valley would reach 6 to 9 m.