Abstract:

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.

Key words: Badong, weak-soft zone, mineral component, structure, physico-mechanical characteristics, landslide