Study On Dynamic Mechanical Property And Constitutive Model Of Ice-Rich Frozen Soil

With the growth of the national economy and the advancement of western development,ice-rich frozen soil in cold regions engineering and the process of artificial freezing method unavoidably bear the impact loads of blasting,vibration,and other forces.Studying the dynamic characteristics of ice-rich frozen soil can provide a theoretical and experimental basis for safe and rapid excavation in frozen soil areas.Currently,most research on the mechanical properties of ice-rich frozen soil focuses on static and quasi-static ranges,with little attention paid to the under impact loads.In this research,frozen sand with water contents from 15% to 150% and frozen clay with water contents from 20% to 1000% were prepared by soil-ice particle mixing method and slurry method,respectively.Split Hopkinson pressure bar (SHPB)tests of ice-rich frozen soil were carried out under the uniaxial and passive confining pressure conditions.The effects of temperature,strain rate,and water content on the dynamic strength and deformation characteristics of ice-rich frozen soil were analyzed.A highspeed camera test system was used to investigate the dynamic damage and failure mechanism of ice-rich frozen soil specimens.In addition,a dynamic constitutive model for ice-rich frozen soil considering temperature rise damage was established.The main conclusions are as follows:(1)Under uniaxial conditions,the dynamic stress-strain curve of frozen clay with water contents range from 20% to 85% and 1000% can be divided into three stages:elastic,plastic,and failure.At water contents of 120%,170%,240%,and 400%,the stress-strain curves exhibit a double-peak phenomenon.Within the water content range from 20% to 53%,the dynamic peak strength and energy dissipation density of frozen clay increase with increasing water content.In the range of 53% to 400%,both the peak strength and energy dissipation density decrease with increasing water content,while there shows a slight increase in peak strength at 1000% water content.With the increase of water content,the peak strain shows a regular of first decreases,then increases,decreases again,and finally slightly increases four stages.The water content inflection points appear at 53%,85%,and 400%,respectively.The dynamic peak strength,strain,and energy dissipation density of ice-rich frozen clay under passive confining pressure exhibit significant temperature and strain rate effects.With increasing strain rate,the dynamic peak strength,peak strain,and energy dissipation density gradually increase,and the amplitude is affected by the water content.With decreasing temperature,both the dynamic peak strength and energy dissipation density of frozen clay with different water contents gradually increase.(2)Under passive confining pressure conditions,the stress-strain curve characteristics of ice-rich frozen clay can be divided into three stages: elastic,plastic,and failure,and the proportion of plastic stage are significantly larger than that under uniaxial loading condition.When the water content is lower than 240%,the trend of peak strength with water content is consistent with that under uniaxial conditions,and it increases first and then decreases with the increase of water content when the water content increases from 240% to 1000%,the peak strength gradually increases with increasing water content.Within the water content range from 20% to 1000%,the range of peak strain fluctuates between 0.035 and 0.052,while the range of energy dissipation density varies between 0.4 and 0.8 J/cm~3.With increasing water content,the growth factors of strength,peak strain,and energy dissipation density increase nonlinearly,indicating that the confining pressure effect of ice-rich frozen clay becomes more significant at higher water contents.(3)The high-speed camera test results indicate that under impact loads,the failure of ice-rich frozen clay specimens is mainly caused by tensile cracks.Within the range of water content from 120% to 400%,there shows an obvious ice-soil layering phenomenon in the ice-rich frozen clay specimens.In the range of 120% to 170%,the soil layer part of the specimen is larger than the ice layer part,and the ice layer part of the frozen clay specimen fails before the soil layer,resulting in the first peak point of the stress-strain curve being higher than the second peak point.In the range of 240% to400%,the total volume of the ice layer part of the specimen is larger than the soil layer part,and the soil layer part of the frozen clay specimen fails before the ice layer,resulting in the second peak point of the stress-strain curve being higher than the first peak point.The final failure mode of ice-rich frozen clay indicates that the frozen clay specimen’s failure degree becomes more obvious with an increase in water content and strain rate.Under passive confining pressure conditions,ice-rich frozen clay specimens exhibit viscous-plastic failure characteristics,and the overall shape remains unchanged,with only a small amount of edge peeling damage.(4)Under uniaxial conditions,the stress-strain curves of ice-rich frozen sand can be divided into three stages: elastic,plastic,and failure.In the range of 15% to 110%,the curves exhibit obvious strain-softening characteristics,however,strain-hardening characteristic appears at 150% water content.As the water content increases,the peak strength of frozen sand shows a three-stage variation feature of "decrease-increasedecrease",with inflection points occurring at water contents of 45% and 60%,respectively.When the water content increases from 15% to 150%,the energy dissipation rate gradually decreases,and the decreasing rate shows a "fast-fast-slow" variation feature,with inflection points occurring at water contents of 37.5% and 45%,respectively.The peak strength,peak strain,and absorption energy of ice-rich frozen sand all show obvious strain rate and temperature effects,but the energy utilization rate only shows temperature effects and is less affected by strain rate.(5)Based on the SHPB test data of frozen soil,the damage of frozen soil specimens under impact load is regarded as consisting of two parts: crack propagation and temperature rise.Based on the theory of heat conduction and energy dissipation,the relationships between temperature rise and deformation of frozen soil specimens during the impact process is calculated.The temperature rise damage variable is defined based on the change in dynamic elastic modulus.A composite damage variable that can comprehensively consider temperature rise and crack propagation is derived based on the strain equivalence theory.The Z-W-T constitutive model considering damage evolution is established,and the stress-strain curves of the constitutive model are compared with the experimental curves.The established constitutive model can describe the influence of water content,temperature,and strain rate on the dynamic compressive strength and deformation characteristics of ice-rich frozen sand.The model is reasonable and effective.Figure [66] Table [12] Reference [132]...