The Influence Factors And Prediction Of Unsaturated Soil Water Characteristic Curve

The soil above the water table is called the unsaturated soil,which is composed of solid particles,pore water and air.It shows different states and engineering properties with different proportion.The soil water characteristic curve is an important parameter in the study of unsaturated soil engineering properties,that is the relationship between matric suction of unsaturated soil and water content,the water content include gravity moisture,moisture or saturation said.The soil water characteristic curve can be used to calculate the permeability coefficient and shear strength.It plays a key role in the analysis of the strength,deformation,seepage,slope stability,and underground migration of unsaturated soils.This paper studies the soil water characteristic curve.1.The influence factors of soil water characteristic curve are summarized,and the experimental research is focused on the mineral composition and particle size,the initial dry density and the applied suction increment.The moisture content of the samples was measured by the pressure membrane apparatus,and then the soil water characteristic curves of the tested soil samples were determined.2.Aiming at the defects of the traditional test methods,which needs high cost and long testing cycle,using the dynamic multi-step outflow method to predict soil water characteristic curve of sand,silt,silty clay and clay,the method does not need the sample in the balanced state,it only needs the relation curve between overflow water and time recorded by computer automatically to calculate the corresponding parameters,the two hydraulic parameters include soil water characteristic curve and permeability coefficient is obtained.In order to avoid the experimental errors caused by the different experimental instruments,the equilibrium soil water characteristic curve measured by the transient water absorption system(TRIM),and the VG model was used to fit it.Through comparing soil water characteristic curve measured by dynamic multi-step outflow method with the test result of equilibrium method,it proves the feasibility of dynamic multi step flow method,this method greatly reduces the test time,and provides a reasonable incremental suction duration of each level and the matrix suction as a reference.3.The micro mechanism of the difference of soil water characteristic curve of soil,sand,silt,silty clay and clay was analyzed by mercury intrusion porosimetry method.At the same time,the pore size and pore size distribution curves of soil samples with different hydraulic paths(different suction increments)were measured.