Elastoplastic Damage Constitutive Model And Creep Characteristics Of Frozen Soil Containing Ice Lenses

The strength and deformation properties of frozen soil are significant indexes to evaluate the stability and safety of infrastructures during construction and operation in cold regions.In recent years,with the further improvement of foundation deformation requirements in cold regions engineering,the parameters and models of frozen soil mechanics obtained through traditional research ideas cannot meet the needs of engineering design and stability calculation.The particularity and complexity of frozen soil are mainly reflected in its sensitivity to temperature changes and its own structural deformation features.This paper focuses on the influence of internal structural characteristics on its mechanical properties and deformation behavior.Based on the full understanding of the effects of structural types,temperature,and stress conditions on the mechanical properties and deformation failure of frozen soil,the relationships between mechanical parameters of frozen soil with different structural types,temperatures,and stress conditions are established by conducting indoor test,theoretical analysis,and numerical calculation.The elastoplastic damage constitutive model and creep constitutive model of frozen soil considering ice-frozen soil interface are constructed and verified.The mechanical behaviors of frozen soil containing ice lenses are studied using the cryogenic-direct shear test system and GDS triaxial test system.The effects of structural types,temperatures,and stress conditions on the mechanical properties of frozen soil are analyzed.The influence of temperature and stress on the shear strength,shear modulus,cohesion,and internal friction angle of frozen soil with different structural types are studied quantitatively.The relationships between strength,elastic modulus,Poisson’s ratio,and confining pressure of frozen soil with different structural types are established.The variations of cracking strength and dilatancy strength of frozen soil with different structural types under various confining pressure are analyzed,and the failure mechanism of frozen soil under different stress conditions is revealed.Based on the shear behavior of ice-frozen soil interface under different temperatures and stress conditions,the effects of initial water content and initial void ratio of frozen soil,and temperature on interface shear strength,friction angle,and cohesion are analyzed.And the structural coefficient is defined to characterize the exertion degree of interface structure in the shear process.The shear stiffness expression of the ice-frozen soil interface considering structural properties was derived.The evolution laws of interfacial shear stiffness with normal stress,initial water content,and initial void ratio were studied,and the formation mechanism of interfacial strength and damage evolution process of ice-frozen soil were revealed.By introducing rheological elements to simulate the mechanical behaviors of cementation and friction of the interface,an elastoplastic constitutive model of the interface in the shearing process is established.Based on the test results of frozen soil containing ice lenses under different stress conditions,the crack initiation criterion and propagation path of frozen soil under triaxial stress are studied.For the homogeneous frozen soil without ice lens,shear failure is dominant under loading,while for the heterogeneous frozen soil,the failure surface is mainly formed by the propagation and penetration of the wing crack at the end of ice lens.Based on the principle of Continuous Damage Mechanics and strain energy theory,the macro and meso coupling damage factor of frozen soil is established,and the effects of the inclination,quantity and length of lens ice and the ice frozen soil interface on the coupling damage factor are analyzed.According to the assumption of strain equivalence,the elastic matrix of frozen soil containing ice lens is modified,and the elastoplastic constitutive model of frozen soil is established by using the relevant fluidity criterion and D-P criterion.The PDE module in COMSOL is used to reconstruct the model,and the rationality of the model is verified according to the test results of heterogeneous frozen soil under different stresses.Based on the creep tests of frozen soil containing ice lenses under different stress conditions,the effects of deviatoric stress and structural type on the creep characteristics of frozen soil are analyzed.And the initial elastic modulus and long-term strength of frozen soil with different structural types are determined.The hardening factor and damage factor of frozen soil in the creep process are defined,and the characteristics of the hardening effect and damage effect in the creep process are analyzed.The effects of ice-frozen soil interface friction coefficient and ice lens inclination angle on damage variables are studied.The ice-frozen soil interface friction coefficient has a greater influence on damage variables than ice lens inclination angle.The mechanical characteristics of interface not only affect the initial value of damage variables,but also determine the creep time when the damage variables are close to one.By introducing the hardening factor and the damage factor into the classical Nishihara model,the creep constitutive model of frozen soil is constructed,and the correctness of the model is verified.The mechanical parameters of frozen soil containing ice lenses under different thermal conditions are studied,the elastoplastic damage constitutive model and creep model of frozen soil containing ice lenses are established by considering ice-frozen soil interface.The results provide a certain reference for controlling the deformation and failure of permafrost foundations in cold regions.