Preliminary Study On Non-darcy Permeability Of Saturated Fully Weathered Mudstone Of Niejiashan Formation In Xiangxi River

The change of water level in the three Gorges reservoir area has a great impact on the stability of the wading slope in the reservoir area.There are a large number of gentle slopes with mudstone as the main stratum in the reservoir area,and permeability is an important factor in judging the stability of landslides.In order to explore the non-linear permeability characteristics of fully weathered mudstone,a high pressure saturated permeometer has been developed,which can be used to measure the permeability coefficient of soil under high permeability pressure difference.Taking the fully weathered mudstone on the deep water slope near the landslide of Xiangxi River in Xingshan County,Yichang City,Hubei Province as the research object,this paper probes into the changes of seepage characteristics of fully weathered mudstone with different initial dry density under high osmotic pressure caused by the change of higher water level,and puts forward the corresponding fitting formula.In this paper,the changes of seepage eigenvalues of fully weathered mudstone under different dry densities are studied,and the corresponding fitting formulas are obtained,and the fitting parameters of different eigenvalues in the application of this formula are explored.The main contents and conclusions of this paper are as follows:1)Darcy flow and non-Darcy flow.A)this paper introduces Darcy’s law from two aspects of Darcy’s seepage test method and the application of Darcy’s law in each case,and summarizes the previous process of putting forward permeability coefficient and permeability.The derivation process of Darcy’s law is summarized on the background of capillary model and hydraulic radius model.B)this paper introduces the seepage phenomenon of non-Darcy flow and briefly introduces the previous research experiments on the phenomenon of non-Darcy flow,introduces and summarizes the upper and lower limits of non-Darcy flow,and summarizes the exploration process of non-Darcy flow seepage formula.2)Development of high pressure saturation permeation meter.In this paper,in order to meet the requirements of higher osmotic pressure,a high pressure saturated permeation meter has developed independently,in which the pressure head is provided by the pressure machine,the water source is provided and the water head pressure is adjusted by the water storage tank.The infiltration test device adopts STS-55 saturated permeation meter,weighs the seepage quality by electronic balance,and records and calculates the seepage quality through the self-developed LABVIEW program window.3)non-Darcy penetration test.A)the permeability coefficient of the soil sample with low initial dry density is constant at the initial stage of seepage,and then increases with the increase of pore pressure,then decreases with the increase of pore pressure,and finally remains constant,which accords with the linear permeability relationship.The whole seepage process includes four stages:the first linear stage,the seepage acceleration stage,the permeability coefficient reduction stage and the final constant stage.B)there is a start-up pressure head in the soil sample with higher initial dry density,and the seepage begins when the pore pressure reaches the start-up pore pressure.In the initial stage,the permeability coefficient increases with the increase of pore pressure,then decreases gradually,and finally keeps constant in accordance with the linear permeability relationship.C)the rationality of the test data is verified by F formula and Hansbo non-Darcy formula,and the non-Darcy seepage formula which is more suitable for the landslide of Mining Bureau is obtained.4)the effect of different initial dry density on the saturated permeability coefficient.A)the four saturated permeability coefficient eigenvalues of soil samples will decrease with the increase of initial dry density.The relationship between the eigenvalues of soil samples is as follows:initial saturated permeability coefficient K₀<saturated permeability coefficient final value K_e<saturated permeability coefficient average valueKsaturated permeability coefficient maximum value k_m,and the average value of saturated permeability coefficientK is closer to the final value of saturated permeability coefficient K_e.B)In order to describe the relationship more accurately between the initial saturated permeability coefficient k₀,the maximum saturated permeability coefficient km,the final saturated permeability coefficient K_e,and the average saturated permeability coefficient?k,the empirical formula of the relationship between the initial dry density and the initial dry density of soil samples,the formula parameters corresponding to different seepage characteristic values are obtained.It is found that the relevant parameter c of the empirical formula will increase with the increase of the permeability coefficient of the soil sample,and the parameter m will decrease with the increase of the permeability coefficient of the soil sample.