Study On Incremental Nonlinear Transverse Isotropic Constitutive Model Of Unsaturated Soil

Natural foundations and large-scale filling foundations are mostly unsaturated soils,and they have the transverse isotropy characteristic.With the development of national urbanization and the implementation of the “One Belt and One Road” strategy,large-scale landfill projects such as flattening mountains,filling trenches and land reclamation were developed.That is,the area of transverse isotropic soils has increased dramatically.Scientifically predicting the deformation of unsaturated soil transverse isotropic foundations is crucial to the design of foundations.The development of modern soil mechanics and geotechnical engineering shows that the incremental nonlinear constitutive model of soil has strong vitality.However,a constitutive model that can simultaneously reflect the unsaturated state,transverse isotropic,and nonlinearity of soil has not been proposed yet.In this paper,through systematic theoretical analysis and lab oratory tests,the mechanical properties and constitutive models of unsaturated transverse isotropic soils are systematically studied.First,the factors of matric suction,initial dry density and loading and unloading are considered respectively,incremen tal non-linear constitutive model of unsaturated isotropic transverse soil has been improved in many aspects,extending its scope of application.Next,based on the theory of unsaturated soil mechanics and elasticity,established an incremental nonlinear transverse isotropic constitutive model for unsaturated soils,and a method of determining all model parameters using unsaturated soil triaxial tests is proposed.Again,unsaturated soil triaxial test with various stress paths were carried out(A total of 6 kinds of 100 test soil samples),revealing the deformation strength characteristics and water volume variation characteristics of unsaturated transverse isotropic soils.Fourthly,the variation law of model parameters with stress state is analyzed and the corresponding mathematical expressions are put forward.Finally,unsaturated soil triaxial apparatus and unsaturated soil true triaxial apparatus were used to carry out unsaturated soil tests separately under different conditions.The rationality of the constitutive model established in this paper is preliminarily verified.The research results of this paper can provide scientific basis and theoretical support for the design of natural layered foundations and large-area filling projects.It enriches and develops the constitutive model theory of unsaturated soil mechanics.