科研之友
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摘要
The original granite joints are retained in the highly weathered stage and called as relict joints. It is often filled with Fe-Mn oxides, showing a thin interlayer of brown to black, which is significantly different from the surrounding matrix as soil interlayers and has an important impact on slope stability in tropical and humid regions. Soil mineral composition, chemical composition, micro-structure and pore size distribution of granite residual, completely weathered and relict joint soils from a weathered granite slope of Chencun in Rongxian of the southeastern Guangxi were respectively studied by X-ray diffraction ( XRD), scanning electron microscopy ( SEM), energy spectrum and mercury intrusion analyses; meanwhile, the evolution process of relict joints and the influence on slope stability were discussed. The results show that the main clay mineral compositions of granite residual and completely weathered soils are kaolinite and quartz, and a small amount of illite. The kaolinite in completely weathered soils has a book-shaped structure with a single crystal size of about several microns to tens of microns; the kaolinite in residual soils is fragmented gradually, the single crystal size is smaller and micro-structure is disordered. The main mineral types of relict joint soils are hematite and birnessite. In initial weathering stage, the colloids of Fe-Mn oxides are spherical and granular in shape, the particle pore size is mainly in the range of several microns to tens of microns, and the surface is porous honeycombed with a large specific surface area and colloidal activity; as weathering continues, the colloid particles of Fe-Mn oxides show the ellipsoidal compact arrangement pattern to the patchy and directional arrangement pattern along the joint direction; the honeycomb structure of colloidal particles disappears gradually, and the specific surface of particles decreases gradually, and the roundness also decreases. The saturated permeability coefficient of residual joint soils is about two orders of magnitude lower than that of completely weathered soils on both sides, the joints are preferential flow paths in the early stage of weathering, and gradually transform into low permeability interlayers in highly weathered granite, which affects the percolation process of groundwater in weathered soils, and has adverse effect on slope stability.
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