Mechanical Behavior And Thermodynamic Constitutive Model Of Frozen Silty Clay

Understanding the mechanical behavior of frozen soil under complex stress conditions is an important basis for the design and construction of frozen soil engineering.The mechanical tests under different loading conditions were carried out to investigate the mechanical behavior of frozen Genhe silty clay in this paper.Then,the mechanism of mechanical behavior of frozen soil was investigated from the view of energy evolution based on the measured heat dissipation and strain energy data.Finally,a thermodynamic constitutive model of frozen silty clay was established considering the universally applicable thermodynamic theory based on triaxial test data.The accurate of this constitutive model was availably verified.The main results and conclusions are as follows:(1)The deformation and strength characteristics of frozen Genhe silty clay under different loading conditions were investigated through triaxial monotonic loading and unloading cyclic tests with different stress paths.The results show that the stress-strain curves of frozen silty clay are affected by confining pressure and stress path.The stiffness shows a first rapid decrease and then tending to a constant with the development of strain.And the degree of deterioration depends on the confining pressure and stress path.The strength firstly increases,then decreases,and finally tends to a constant with the increase of mean stress.As the increment decrease of direction angle of stress,the strength firstly increases and then decreases.(2)A method for calculating heat dissipation during loading and deformation of frozen soil was proposed based on triaxial test and bending element test of frozen soil.The heat dissipation and its evolution laws during the process of triaxial test were obtained by this method.The heat dissipation rapidly increases at first with the increase of axial strain,then slowly increases,and finally basically stabilizes.The higher the stress level is,the greater the heat dissipation is.(3)The strain energy of frozen silty clay under during the load and deformation processes was calculated based on the stress-strain data of triaxial test,and the evolution laws of it were analyzed.The elastic and plastic strain energy nonlinearly increase with the increase of axial strain.The proportion of elastic strain energy in total strain energy is much lower than that of plastic strain energy.The larger the confining pressure is,the smaller the direction angle of stress increment is,the greater the proportion is.Based on the laws of energy evolution and damage theory,the damage factor was defined by the ratio of elastic strain energy and critical elastic strain energy.The damage evolution laws of frozen silty clay were analyzed.The damage of frozen silty clay increases with the development of strain,but its growth rate continuously slows down.The greater the confining pressure is,the slower the damage development is.The impact of stress path on the development of frozen soil damage is inconsiderable.(4)Based on the mechanical properties of frozen Genhe silty clay obtained from mechanical tests,the free energy function and dissipation function of frozen silty clay were obtained by combining thermodynamic theory.The elastic law,yield criterion,flow law,and hardening law of frozen silty clay were derived by using the thermodynamic constitutive modeling method through two energy functions,and the thermodynamic constitutive model of frozen silty clay was established.Model parameters were determined by triaxial test data,and the models was availably verified by triaxial test results of different stress paths.The results show that the model can well predict the stress-strain behavior of frozen Genhe silty clay.