Seepage Properties Of Low-permeability Soft Soil

Soft soil has tiny particles,large specific surface area,abundant charge on the particle surface and unbalanced force between different components of soil.For soft soil,the interactions between soil particles and liquid cannot be ignored because of those characteristics talked above and have significant influences on engineering.In this paper,the seepage characteristics of low permeability soft soil are studied by means of experimental analysis and theoretical investigation.Artificial soil,consisting of different mineral compositions and ionic solutions has different micro parameters.Firstly,the relationships between micro parameters and permeability characteristics can be studied by changing the components and ion concentration for changing the micro parameters of soft soil.Secondly,based on the pore scale test,the relationships between the spatial distribution of porosity and permeability can be obtained.Thirdly,on the basis of soft seepage equation which has mixed flow of free water and bound water and Darcy`s law,establish the seepage model of low permeability soft soil by considering the pore scales.The main work and achievements are as follow:(1)Study the effects of micro parameters on the seepage properties of soft soil.The seepage experiments are carried out on the artificial soft soil with different mineral composition and pore liquid ion concentration.The specific areas are obtained by mercury injection test.The electric field intensity of soft soil is different with different mineral composition,pore liquid ion concentration and specific surface areas.The macro seepage properties are controlled by micro-electric field which is effect by the properties of pore liquid and the effective pore size.(2)Study the relationship between pore size distribution and permeability coefficient.According to the experimental results and theoretical analysis,the pores in the soft soil are divided into small pores(D ≤ 350nm),middle pores(35nm0<D≤10000nm),large pores(D > 10000nm).The permeability coefficient of soft soil is strongly correlated with the average pore size,the volume of small pores and the volume of middle pores.The permeability coefficient of soft soil is moderately related to the volume of large pores.(3)Based on the pore size distribution,establish the seepage model of soft soil.Micro-electric field effect is taken into consideration in the model.The pore liquid is divided into free water with Newton fluid characteristics and the bound water with non-Newton fluid characteristics in the model.The characteristics of pore size distribution of soft soil are taken into account in order to modify Darcy flow equation.The model considering pore liquid properties and pore size distribution characteristics is more consistent with the actual situation and more suitable for soft soil than Darcy’s law.