巴东新城区库岸斜坡软弱带特征

Characteristics of weak-soft zones of Three Gorges Reservoir shoreline slope in new Badong county

巴东新城区巴东组第3段(T2b3)内广泛分布软弱带,通过钻孔岩芯分析、地表调查、X射线衍射、电镜扫描和物理力学性质试验,研究软弱带的特征。白土坡和西壤坡库岸深300余米的监测孔显示,库岸斜坡巴东组第3段内发育有13层贯通的软弱带,表现为富含黏土质的软弱夹层、碎裂岩软弱带、溶蚀改造软弱带和软岩软弱带。软弱带的矿物成分以绿泥石、伊利石、石英和方解石为主,黏土矿物含量变化较大,多者可达70%。软弱带经历了层间剪切变形,并牵引周围岩体形成较宽的破劈理或碎裂岩带,其微观结构显示的擦痕及矿物定向排列线理,揭示了软弱带经历了顺层剪切滑动,并伴有重力蠕滑特征。软弱带物理力学试验显示;在反复剪切和地下水长期作用下,其剪切强度将大幅下降。这些特征说明,三峡水库全面蓄水后,软弱带在地下水长期作用下必将加剧库岸斜坡的深部形变,进而发生沿软弱带的深部蠕滑。

Several stable and continuous weak-soft zones exist in the Third segment of Triassic Badong Formation strata（T2b3） in New Badong county.The characteristic of weak-soft zones was studied by drilling core analysis,surface investigation,X-ray diffraction（XRD）,scanning electron microscope（SEM） and physico-mechanical experiment.Based on geological prospecting data of monitoring profile（300m deep） the paper indicated that 13 strips transfixion weak and soft zone existing in the T2b3 strata can be divided into weak intercalation being rich in clayish fine,cataclasite weak and soft zone,corrosion transformation weak and soft zone and soft rock weak and soft zone according to the substance in weak and soft zone and structural characteristics.The weak-soft zones are composed of illite,chlorite,quartz and calcite etc,whose clay mineral has difference contents and could is more than 70%.The weak-soft zones undergo interlaminar shear failure and influence surrounding rock mass which form fracture cleavage or cataclasite zone.The microstructure of weak-soft zones shows that the scratch and mineral’s directional alignment are obvious;it is indicated that the weak-soft zone experienced bedding-parallel shearing slip and local gravitational creep structure of shoreline slope.Test results show that shear strength becomes lower once the i weak-soft zones attract water to saturation and repeated shear.The weak-soft zones will aggravate deep deformation of shoreline slope under long term soak when storage water level is uplifted to 175m in Three Gorges Reservoir.