Study On Unsaturated Soil Model Based On Soil Water Characteristic Curve

Unsaturated soils exist widely in nature and show different engineering properties due to the change of three-phase ratio.Constitutive theory and permeability coefficient are the key points in the study of unsaturated soil such as slope stability,soil settlement and deformation,and underground migration of pollutants.However,researches on unsaturated constitutive theory and permeability coefficient involve the relationship between soil and water characteristics.The unsaturated constitutive model considering elasto-plastic deformation and capillary hysteresis cycle is improved,and a prediction model for rapidly calculating unsaturated permeability coefficient is established,where are based on the soil-water characteristic curve.The research is mainly divided into the following aspects.(1)Based on the internal variable theory of capillary hysteresis,a hydraulic coupling constitutive model of unsaturated soil is established.The model can describe the coupling effect of unsaturated soil elastoplastic deformation and capillary hysteretic cycle,considering not only the influence of moisture content change on material deformation,but also the influence of residual gas content change on the relationship between cyclic soil-water characteristics and mechanical properties of soil.The model program is written in FORTRAN language,and the prediction results are obtained.By comparing with the experimental results in the literature,it is proved that the model can simulate the hydraulics behavior of unsaturated soil well.(2)Based on the principle of dynamic multi-step flow method,the hydraulic parameters of unsaturated silt are measured on the improved pressure plate tester test system.When the sample is in the non-equilibrium state,the soil-water characteristic curve and permeability coefficient of the unsaturated soil can be obtained,and compared with the test results in the equilibrium state,it is proved that the method can quickly and easily obtain the soil-water characteristic curve.(3)Based on soil-water characteristic curve and unsaturated permeability coefficient prediction model,a combined model of Feng & Fredlund and Childs & Collis-Geroge model was established,and compared with the traditional VGM model,the feasibility of the combined model was proved,which laid a foundation for the establishment of seepage deformation theory under arbitrary dry-wet path.