小湾水电站坝址区低高程岸坡表生改造特征及机制研究

摘要：小湾水电站坝基、水垫塘边坡及低高程排水洞系统广泛地揭示了低高程岸坡的地质特征。基于现场调查和二维弹塑性有限元分析，深化认识了低高程岸坡表生改造特征：（1）它是在建造和构造改造的基础上进行的：原构造缓倾角节理扩展、错动；陡倾角节理扩展、产状改变以及错动；新生了大量中缓倾角裂隙；表生改造程度向坡内减弱。（2）建立了低高程岸坡表生改造缓裂生成机制模型，分析了其生成过程。（3）在二维弹塑性有限元分析中，基于拉破坏区分布、剪应变和点安全度等指标，分析了低高程岸坡卸荷松弛范围，其中谷底表生改造明显影响深度为6~9m。

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.