Study On The Mechanical Properties And Constitutive Damage Model Of Seasonal Cohesive Frozen Soil

Most of the subgrade construction in northern China is carried out on seasonal frozen soil or long-term frozen soil layer.Under the condition of negative temperature in winter,the pore water inside the frozen soil will become solid ice,which makes the frozen soil have the mechanical characteristics of rock like;at the same time,the solid ice,liquid water and gas in the frozen soil are mixed with each other,which makes the deformation of frozen soil and rock in essence And the rheological property of frozen soil under external load is also more obvious than that of rock.These complex internal factors and external factors such as temperature,stress and other external factors lead to the instability and cracking of roads and structures on the upper part of the Subgrade after the completion of the project.In order to obtain the deformation mechanism of frozen soil under the above complex factors,and further improve the mechanical analysis theory of seasonal viscous frozen soil,a triaxial constitutive model and a creep damage model suitable for describing the deformation of frozen soil are established by using damage mechanics theory,which provides a new idea for the development of frozen soil mechanics.Finally,taking the subgrade engineering of Da DongGang Heda expressway as the background,aiming at the problem of uneven settlement of subgrade caused by design and calculation defects,the triaxial damage constitutive model and creep damage model of frozen soil are programmed to analyze the stress and stress under the action of subgrade soil load by means of damage mechanics theory,indoor triaxial test and numerical simulation analysis The change law of deformation and prediction of deformation law.The main work is as follows:(1)Triaxial tests were carried out on clay with large water content under the coupling effect of temperature and stress.The stress-strain relationship,volumetric strain axial strain relationship and strength parameter variation law of frozen soil under the coupling effect of temperature and stress were analyzed.Based on the statistical damage theory,strain equivalent hypothesis principle and elastic energy release rate,a constitutive model which can reflect the strain softening deformation characteristics of frozen soil is constructed.By comparing the model curve with the experimental curve,it is found that the established model can truly reflect the damage and deformation characteristics of frozen soil in the loading process and can better reflect the elastic performance of frozen soil during the loading process Evolution law..(2)By adopting the deterioration law of the elastic modulus of frozen soil before and after freezing,the damage variable of the soil sample during the freezing process is defined.It is believed that the creep deformation process of frozen soil is also a process of continuous accumulation of damage and continuous deterioration of mechanical parameters.Furthermore,damage variables related to freezing and creep coupling are constructed.The Nishihara model is nonlinearized based on the theory of fractional order and unsteady parameters,and it is believed that the fractional order is also affected by the creep time.Then a new type of unsteady fractional order Nishihara creep damage model was established.By comparing the experimental data with the model curve,it is obtained that the model can describe the creep deformation of frozen soil well and overcome the shortcomings of the traditional model that cannot describe the law of accelerated deformati.(3)By combining the above research on the content of the frozen soil deformation of the Dadonggang Expressway roadbed,the finite element software FLAC3D software was developed again.The simulation analysis of the roadbed settlement and horizontal displacement during the layered filling process of Dadonggang-Heda Expressway under different temperatures is carried out.This can effectively predict the frost heave and deformation law of Dadonggang roadbed under different freezing temperatures,and timely warn the uneven settlement of the roadbed.(4)The secondary development is carried out in the finite element FLAC3D environment,and the unsteady fractional order creep damage model of the dual-process coupling of freezing and creep will be constructed reasonably.The creep damage variable of frozen soil is used to calculate the creep curve of frozen soil,and the comparison and analysis with experimental data verify the reliability of the model.Furthermore,the characteristics of freezing creep settlement of roadbed under different temperature conditions are analyzed.This effectively guarantees the long-term stability of the roadbed structure during highway construction and guarantees the quality of highway construction.