Thermodynamics Constitutive And Experimental Studies On Static And Dynamic Behavior Of Saturated Soils

The static and dynamic behavior of soil under different drainage conditions and stress paths is greatly complicated and diverse,and research or theoretical prediction are of great significance to the design and theoretical analysis of geotechnical engineering structures.In particular,it is still challenging and difficultthe to establish a constitutive theory for predicting the behavior of soil under cyclic loading.At the same time,the cementation between soil particles is a key scientific issue for the establishment of mechanics models for artificially modified soil.Therefore,it is necessary to study the static and dynamic behavior of general soil and cemented soil,and establish constitutive theory model that uniformly considers its static and dynamic behavior.First,we establishes the basic physical conservation equations and thermodynamic identities satisfied by saturated soils,and obtains the elastic and plastic constitutive relations of saturated soils,including the effective stress principle based on nonlinear hyperelasticity,the energy dissipation based on non-equilibrium thermodynamic theory and expressions for inelastic strain.The models that established in this paper have clear physical meaning and theoretical background.The model firstly shows the elastic potential energy function applicable to the soil material,deriving the nonlinear hyperelastic constitutive relationship that can characterize the elastic behavior of saturated soil,which relates to the density and pressure,and introduces the third invariant of elastic strain to reflect Stress-induced anisotropy of elastic stiffness.On the other hand,considering the thermodynamic equilibrium state stability,the model can naturally obtain the effective stress state boundary surface of the soil,thereby linking the strength criterion with the nonlinear elastic stability of the material.Using this model,we simulate the experimental result of unit tests under various stress paths,verifying the validity of the model.The results show that the model can effectively predict the drained and undrained monotonic shear behavior of saturated sand and clay with different shear paths,initial shear stress and soil structure.On the basis of the constitutive model above,we further introduces the concepts of locked elastic energy,locked elastic strain,configuration entropy and cementation state parameters,and obtained thermodynamic dynamics constitutive model that can predict the cyclic shear behavior of sand and cemented sand.In particular,the influence of shear energy dissipation on the structural and dynamic behavior of sand is considered through the concept of configuration entropy.This model can better simulate the mechanical behavior of sand before and after liquefaction,as well as the effect of cementation and its degradation on cemented sand.Then,we introduces the average particle energy factor,and further considers the influence of particle gradation and particle breakage on the macro-elasticity and mechanical behavior of soil.At the same time,in order to verify the models and study the dynamic behavior of sand or cemented sand,we carried out a series of undrained cyclic triaxial compression tests for Fujian standard sand,studying the influence of particle gradation and Particle breakage.The test results show that the particle gradation,fine particle content and dissipation of cementation have complex and mutually coupled effects on the development of excess pore pressure and strain under undrained cyclic shear.Using the test results above,we verifies the dynamic constitutive model established in this paper,showing that the model can effectively reflect the complex cyclic shear behavior of sand and cemented sand.