Research On Microstructure And Seepage Characteristics Of Compacted Granite Weathered Soil

Granite weathered soil is widely distributed in southern China,so it is used as a cheap engineering material as a filler for high-speed railways and highways.However,under the action of rainfall and external pressure,the weathered granite soil with lower dry density will cause subgrade deformation,slope instability,and landslides.Therefore,the use of weathered granite soil as a building filler needs to be compacted to improve soil properties to meet engineering needs.This paper takes the weathered granite soil in southeast Guangxi as the object to study the influence of dry density on the microstructure and seepage characteristics of weathered granite soil.The pore network model is extracted through the micro-CT scan test and the advanced digital image processing technology in the Avizo software.The model can visually present the size,shape,connectivity and distribution of pores and throats,and perform quantitative characterization.Then,based on the traditional method of fluid mechanics(CFD),the digital reconstruction model of the actual pore structure was imported into Comsol to simulate the seepage flow at the microscopic scale,and the influence of dry density on the seepage characteristics of weathered granite soil was studied from the microscopic point of view.According to the distribution law,the saturated permeability coefficients along the X,Y,and Z directions are calculated and compared with the measured saturated permeability coefficients to verify the accuracy and representativeness of the actual pore structure digital reconstruction model.The main conclusions are as follows:1.From the three aspects of tortuosity,average coordination number,and uniformity of coordination number distribution,it is shown that with the increase of dry density,the connectivity of weathered granite soil gradually deteriorates.With the increase of dry density,the pore tortuosity of weathered granite soil gradually increases,and the average coordination number gradually decreases,and the uniformity of the coordination number distribution gradually becomes worse.The average coordination number of connected pores of weathered granite is between 3-7,and the coordination number is mainly distributed between 1-10.2.With the increase of dry density,the number of small pores in weathered granite soil increases exponentially,the proportion of pore volume larger than 52?m gradually decreases,and the pore size distribution range narrows;the pore volume is mainly composed of pores with larger equivalent diameters.provide.The average pore volume,throat radius,and throat length of granite fully weathered soil gradually decrease with the increase of dry density,while the average pore volume,throat radius,throat length and dry density of granite residual soil have no obvious correlation.The throat radius and length of weathered granite soil are unimodal with good homogeneity.3.During the seepage process of weathered granite soil,the average seepage velocity and average seepage pressure change range and trend of each section are roughly the same.The average seepage pressure decreases as the distance to the seepage inlet increases;the maximum velocity appears in connectivity In a good pore center area,and far beyond other parts,along the direction of the pore center to the outer wall,the seepage velocity gradually decreases;in areas with poor connectivity,the flow velocity is almost zero.With the increase of dry density,the pore connectivity of weathered granite soil deteriorates,the pore structure of each section changes,and the average seepage velocity of each section gradually decreases,which indicates that dry density is important to the seepage characteristics of weathered granite soil.influences.4.The average saturated permeability coefficient of granite residual soil with dry density of 1.485,1.65 and 1.815g/cm~3 is 0.9,1.35 and 0.77 times of the measured value respectively.The average saturated permeability coefficient of completely weathered granite soil with dry density of 1.674,1.86 and 2.046 g/cm~3 is 1.25,5.2 and 1.66 times of the measured value respectively.The pore space model can accurately represent the real pore seepage characteristics of soil.