| The topography of the North Mountain in Xining is steep,with a large amount of colluvial deposits accumulating along the foot of the slope.These sediments are mainly composed of the quaternary loess,tertiary gypsum bearing mudstone,and argillaceous sandstone.Formed by colluvium and weathering,the engineering geological stability of rock and soil mass is poor.Effected by human activities and irrigation,geological disaster occurs frequently,which not only threats the safety of people's lives and property,but also restricts the urban development.Since the composition and microstructure of colluvial rock and soil determine its macro-mechanical properties,it is of great significant to conduct relevant research.To analyze the composition and physical properties of the colluvial deposits in Xining,this study is carried out by means of soluble salt content determination,X-ray diffraction,and particle analysis.The microstructure of colluvium is detected and quantitatively characterized by using the scanning electron microscope experiment(SEM)and Image-Pro Plus software.The main achievements are as follows.(1)The clay minerals of the colluvial deposits in Xining mainly are mainly composed of illite,chlorite,and kaolin,while the non-clay minerals include quartz,albite,dolomite,calcite,and gypsum.The content of non-clay minerals is higher than that of clay,which proved that the engineering properties of poor structural stability.(2)In the leaching solution of colluvium in the North Mountain,the content of sulfate ion is the highest(2792.26?3850.56 mg/L),followed by the hypochlorite ion content(2620?3284 mg/L),while the carbonate ion and bicarbonate ion content is relatively low.The mineralization degree is 2620?3284 mg/L,and the soluble salt type is Ca Cl2+Na Cl+Na2SO4,which shows obviously salinization and alkalization characteristics and is highly corrosive to concrete buildings.(3)At the study area,the average particle size of the fine grained soil of the colluvial sediments is 0.0027?0.0648 mm.The difference in soil particle size distribution and permeability are large,which can be characterized as poor separation and unstable structure.For the physical and mechanical properties,the characteristics of the colluvial deposits are hard plastic silty clay,with slightly wet,medium density,medium water permeability,medium compressibility,and low shear strength.(4)The microstructure image of colluvial deposits at the Micron scale was obtained by scanning electron microscopy test.The soil structure of colluvial deposits can be divided into8 particle forms,4 particle contact modes,2 particle arrangement modes,5 pore types,3cement types and 3 cementing methods.The complicated and changeable structural morphology resulted in the inhomogeneity of the collapsed product,which further lead to the variability of its macrostructure and the instability of its mechanical properties.(5)Using the IPP software,the quantitative characteristic parameters,such as the size,quantity,shape and orientation of the colluvial pores,were extracted.By comparison,the number of small pores is the most one,accounting for 49.30%?54.70%of the total pores.Then followed by the mesopores,accounting for 35.19%?43.71%.The macropores only accounts for 6.98%?10.35%,while they occupies about 78%?92%of the total area.The pore shapes of colluvial deposits are mostly irregular,and there are few long strips and equiaxed(circular)shapes,which is independent of sampling position.The pore orientation angles of different sampling points are distributed in each interval.The frequency distribution is irregular,and the overall performance is no obvious directionality.Above research results provide theoretical basis for understanding the composition,microstructure,and the cause and mechanism of the geological disasters of the colluvial deposits.Besides,it would be also helpful for the establishment of geological disaster prevention system and scientific decision making in Xining. |
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