Unsaturated Elasto-plastic Constitutive Model Of Ili Loess Considering Soluble Salt Content

With the construction of basic engineering in western China,a large number of water conservancy projects have been carried out in Ili,Xinjiang.The Ili valley surrounded by mountains on three sides,with the perennial influenced by west wind climate,make the distribution in the valley of the terrace on both sides of the collapsibility loess has the characteristics of large wetting deformation,high soluble salt content,is obviously different from the loess plateau in monsoon area.The wetting deformation is composed of collapsible deformation caused by the structure and the dissolution.During the operation of hydraulic structures such as canals,the distribution of soluble salt in the surrounding unsaturated soil is uneven due to the movement of water,which affects the deformation and safety of buildings in operation.Taking the Ili loess as the research object,this paper carried out wetting deformation tests under the action of water-density,water-force and water-salt under the lateral confining condition to reveal the law of wetting deformation of Ili loess and the mechanism of the collapse deformation and dissolution deformation in the process of humidification.Meanwhile,the unsaturated soil tests under three stress paths of the net mean stress cycle,the suction cycle and the consolidation shear with different soluble salt contents were carried out.The influence of soluble salt content on the characteristics of deformation and yield of unsaturated Ili loess under wetting-loading,and the critical state characteristic under deviatoric stress are systematically expounded.On this basis,the unsaturated elasto-plastic constitutive model of Ili loess considering soluble salt content is established,which can provide reference for engineering construction in central Asian loess areas such as Ili.The main research results are as follows:(1)Through the wetting deformation tests of Ili loess under the action of water-force and water-density,the variation rules of lateral stress,volumetric strain and degree of the wetting in the process of humidification are revealed.The normalized compression curve considering the effect of dry density is established,which can provide a theoretical basis for the calculation and evaluation of collapsibility for Ili loess.A four parameter expression is proposed to better characterize the collapsibility softening curve of Ili loess under different water contents and dry densities,which provides a basis for rapid evaluation of collapsibility of Ili loess.(2)Based on the double line collapsibility test of loess,a simple and feasible method to distinguish dissolution deformation from collapse deformation is proposed by adding the compression test of humidifying with the saturated salt solution.The interaction mechanism of dissolution and collapse in the process of humidification with different Na Cl contents is studied,which provides a new idea for the study of wetting deformation under the action of water-salt.(3)Through triaxial tests under the isotropic stress with different soluble salt contents,the yield characteristics of unsaturated Ili loess in the process of suction-increase and loading-collapse are measured,and the yield lines of LC and SI for unsaturated Ili loess are verified.Meanwhile,the influence of soluble salt content on the characteristics of deformation,yield and water change of unsaturated Ili loess are explored.Through triaxial tests under the deviatoric stress with different soluble salt contents,the relationship between shear failure strength and soluble salt content of undisturbed Ili loess is analyzed,the yield curves in p-q plane are measured,and the hardening law of yield curve caused by suction and stress are revealed.(4)The change rules of p-q critical state lines under triaxial stress state in the net stress space and effective stress space are studied.The unified descriptions of soil water characteristic curves under different net mean stresses and e-p critical state lines under different suctions are put forward,and the mathematical expressions considering the influence of soluble salt content are established,respectively,which lays a theoretical foundation for characteristics of soil-water and critical state under the influence of soluble salt.(5)Through comparative analysis of triaxial test results,the elasto-plastic constitutive model of undisturbed Ili loess considering soluble salt content is established under the axisymmetric stress state.The rationality of the model is verified by the results of test under the complex stress path,which provides a reference for the prediction of characteristics of mechanical and hydraulic of unsaturated Ili loess.