Research On Nonlinear Permeability Characteristics Of Saturated Clay Considering Microscopic Pore Features

In recent years,with the development of economic globalization,the domestic demand for various military and civilian infrastructure construction has increased,and more consideration has been given to the performance of soil penetration and consolidation.At present,the domestic hot topics of soil permeability research mainly focus on the study of various physical properties of unsaturated soils.Although there is no lack of research on saturated soil seepage theory,due to the nonlinear seepage phenomenon in saturated compact clay,There is a certain controversy when studying the seepage movement of saturated clay and there is a certain deviation from the actual project.However,my country’s rivers and coastlines are widely distributed,and saturated soil is widely distributed in them.Therefore,it is very meaningful to study the theory of saturated soil seepage in consideration of actual conditions.This article takes saturated soil as the research object,carries out pressure plate test,flexible wall GDS penetration test and XRF test under different initial dry density for saturated Hunan clay.Based on the existing test data of Wuhan clay,the theoretical Analyze,derive and summarize the permeability coefficient and nonlinear seepage characteristics of saturated soil under different stresses on the scale of microscopic pores.The specific research and conclusions are as follows:(1)The possible influencing factors of soil permeability coefficient were explored,and the element composition of Hunan clay was studied through XRF fluorescence spectrum analysis test.The test results show that the iron(Fe)element content of Hunan clay is relatively large,the concentration is about 8384 ppm,which is converted into a percentage of about 0.84%.Combined with specific research,it is found that the permeability coefficient of the soil may have a certain impact.(2)By combining fractal theory and saturated permeability coefficient model,the prediction model of permeability coefficient of saturated soil under deformation is derived.It can be used for arbitrary deformation conditions under the condition of only known soil volume/mass water content,matrix suction and void ratio after deformation.The saturated soil permeability coefficient is predicted.Through the analysis and comparison of the existing Wuhan clay test data and the data in the UNSODA database,it is found that the prediction effect of the model is in good agreement with the measured value.(3)The deduced saturated soil permeability coefficient models under deformation conditions all believe that the saturated permeability coefficient is inversely proportional to the square of the air entry value and directly proportional to the maximum aperture.This conclusion has been verified by numerical simulations.(4)The soil-water characteristic curve is obtained through the pressure plate instrument test on Hunan clay,and the soil-water characteristic curve is divided into an index that characterizes the pore size by the capillary law.(5)Through the flexible wall GDS seepage test of Hunan clay,it is found that the seepage velocity and hydraulic gradient in the seepage movement of Hunan clay show a nonlinear relationship.Considering the influence of pore viscous resistance,a nonlinear permeability model considering the initial hydraulic gradient is derived based on the TK model.After comparing the predicted results of this model with the measured values and other models,it is found that the predicted effect of the model is the same as the measured ones.The values are in good agreement.