小湾水电站枢纽区工程地质条件

小湾工程枢纽区地震地质条件复杂，地震基本烈度为Ⅷ度。坝址区地层呈单斜构造。横河展布。陡倾上游，岩性主要为黑云花岗片麻岩、角闪斜长片麻岩。两岸山体雄厚，地下水丰富，埋藏较浅；崩塌作用普遍；卸荷作用强烈，边坡稳定条件较差。岩体中高岭土化蚀变现象较普遍，陡倾角破裂结构面发育，且分布有顺坡中缓倾角节理，存在坝基(肩)抗滑和变形稳定问题。工程区属中高地应力区，地下洞室埋藏深度大，围岩以微风化一新鲜岩体为主，总体稳定条件较好。

Engineering geological conditions of Xiaowan Hydropower Project

The seismic and geologic conditions in the Xiaowan hydropower project area are complicated and the earthquake is of magnitude grade-VIII. The strata are of monoclinal structure and run perpendicular to the river, significantly dipping upstream, which are lithologically composed of biotite and granitite gneiss, hornblende and anorthosite gneiss. The mountains on both banks look magnificent and thick. Groundwater is abundant, buried not far from the ground surface. Landslides often occur in the area, with a thick cumulative mass in quite some places. Load relief action performs intensively in the form of developed tensile fissures, steeply dipping and shearing joints, inclining along slope. As a result of this the slopes are unstable. Kaolinised thermal alteration is widespread, and even appears in belts in some places, developed on sub-EW and SN fractured bedding plane at great dip angles. Moderately and gently dipping joints are distributed along slope. Therefore close attention should be paid to the stability against sliding and deformation at both dam foundation and abutments. The project is located in an area with medium to high stress. The underground chambers are deeply buried with their surrounding rocks mainly composed of slightly weathered to sound rock masses, which are intact and are of high strength. Taken as a whole the project area enjoys fairly good stability conditions.