A Three-dimensional Unsaturated Soil Water Characteristic Surface Model Considered The Deformation And Hysteretic Effect

Soil water characteristic curve describes the relationship between water content(or saturation)in unsaturated soil and matrix suction(or soil water potential)which is one of the most important constitutive relations for describing the hydraulic characteristics of unsaturated soils.There is a hysteretic effect on the soil-water characteristic curve,that is,saturation and suction are not the corresponding relationship in the process of drying and humidification.There are many factors affecting the soil water characteristic curve,in which the influence of deformation is particularly significant.The deformation not only has a great influence on the main drying line and the main wetting line,but also has an unnegligible effect on the scanning line.Therefore,in this paper,the void ratio is used as an index to describe the deformation and a surface model of soil water characteristic surface which considers the effect of deformation and hysteresis is established.The main contents and results are as follows:(1)The current research status of soil water characteristic curves at home and abroad is summarized,including the influence factors of soil water characteristic curve,the soil water characteristic curve model and the application of soil water characteristic curve.In the part of soil water characteristic curve model,the SWCC model of empirical formula fitting,the SWCC model considering the deformation and the SWCC model considering the hysteretic effect are summarized respectively,and the various models are classified.(2)Based on the theory of boundary surface,a three-dimensional soil water surface model of unsaturated soil considering the effect of deformation and hysteretic effect is established.The constitutive equation of the model takes suction and void ratio as independent variables and saturation as dependent variable.First,based on the experimental results,the equation of the main drying edge and the main wetting edge is derived.Secondly,the mapping rule is established to deduce the relationship between the plastic modulus of the boundary surface and the scanning line.Then,the plastic modulus of the boundary interface is determined by the boundary equation,and the plastic modulus of the scanning line is determined by the projection law and the incremental equation of the scanning line is determined.The boundary surface equation and the scanning line increment equation together constitute the constitutive equation of three dimensional soil water characteristic surface considering the effect of deformation and hysteresis.Given any point in the suction-void ratio-saturation space,the scanning line can be determined through the constitutive equation established.(3)Completed the establishment of three-dimensional soil water characteristic surface model in suction-void ratio-saturation three-dimensional space.By using Matlab,the main wetting surface,the main drying surface and the computed scanning line in the three-dimensional soil water characteristic surface model established in this paper are drawn into suction-void ratio-saturation space.Through the analysis,it is found that the increase of suction will lead to the decrease of saturation at the same void ratio,and the increase of the void ratio will also lead to the decrease of saturation under the same suction condition.The area of the hysteresis loop increases with the increase of initial void ratio.(4)The prediction function of the three-dimensional soil water characteristic surface model is realized by programming and the applicability and prediction accuracy of the model are verified by comparison with the test results.The results showed that:when predicting the different test paths of four different soil samples such as pearl clay,silty loam,silica sand and Bentonite/kaolin mixed soil no matter in the two-dimensional plane of suction-saturation and void ratio-saturation or the three-dimensional space of suction-void ratio-saturation,the prediction results of the model coincide with the experimental data well which verifies the applicability and feasibility of the proposed model.