Study On Dynamic Mechanical Property And Constitutive Model Of Artificial Frozen Soil Under Coupled Static And Dynamic Load

Aiming at the state of coupled static and dynamic mechanics characteristic of frozen soil in artificial freezing method engineering.Studies focused on the static or quasi-static behavior of frozen soil have acquired abundant accomplishment.However,there has little research focuse on the stress-strain characteristic,strength and deformation characteristic,failure mode,energy dissipation and constitutive model of frozen soil under coupled static and dynamic load.In this paper,the effects of freezing temperature,strain rate,confining pressure,axial pre-compressive stress,and frozen soil type on dynamic mechanical property of artificial frozen soil are studied with the help of modified split-Hopkinson pressure bar(SHPB).Additionally,the corresponding constitutive models of artificial frozen soil are established.The main contents and conclusions are as follows:(1)The dynamic stress-strain curves of artifical frozen soil under different stress states are analyzed.The results show that,for artificial frozen clay,under uniaxial state,at-5?,dynamic stress-strain curve can be divided into four stages(i.e.,compaction stage,elastic stage,plastic stage and strain slowly softening stage).At-15?,it can be divided into three stages(i.e.,elastic stage,plastic stage and failure stage).For artificial frozen sand,under uniaxial state,dynamic stress-strain curve can be divided into four stages(i.e.,elastic stage,plastic stage,strain slowly softening stage and failure stage).For artificial frozen silty clay,dynamic stress-strain curve can be divided into four stages(i.e.,compaction stage,elastic stage,plastic stage and failure stage)under uniaxial and one-dimensional coupled static and dynamic load.Under active confining pressure and three-dimensional coupled static and dynamic load,it can be divided into three stages(i.e.,elastic stage,plastic stage and failure stage).(2)SHPB experimental results of artificial frozen clay and frozen sand under active confining pressure state show that the dynamic compressive strengths increase with the increase of confining pressure.At the same freezing temperature and strain rate,dynamic compressive strengths of artificial frozen silty clay under three-dimensional coupled static and dynamic load are larger than that under one-dimensional coupled static and dynamic load.With the increase of confining pressure,dynamic compressive strength and first stage deformation modulus logarithmic increase,however,second stage deformation modulus linearly increases. Dynamic compressive strength,first and second stage deformation modulus of artificial frozen silty clay under one and three-dimensional coupled static and dynamic load increases obviously compared with that under uniaxial state.Additionally,both of them first increase then decrease with the increase of axial compressive stress ratio.The peak axial compressive stress ratios are 0.7 and 0.8 for one and three-dimensional coupled static and dynamic load,respectively.There has a similar change rule of strength growth factor and second stage deformation modulus growth factor under different axial compressive stress ratios.Axial compressive stress ratio has a significant effect on first stage deformation modulus growth factor.(3)The failure modes of artificial frozen soil under different stress states are analyzed.Under uniaxial state,brittle failure appears for artificial frozen clay at-15?and artificial frozen sand at-5? and-15?,but it is plastic failure for artificial frozen clay at-5 ?.For artificial frozen silty clay under one-dimensional coupled static and dynamic load,spall phenomenon appears at circumferential direction at 0.4 axial compressive stress ratio.Shear failure appears at 0.7 to 0.9 axial compressive stress ratios.Moreover,comminution mode appears at 1.0 axial compressive stress ratio.Artificial frozen soil specimen has no obvious crack under three-dimensional coupled static and dynamic load.Under the same stress state,dynamic compressive strength of artificial frozen silty clay linearly increase with the decrease of temperature,and growth rates are different for three stress states,dynamic uniaxial state shows the maximum value,followed by three-dimensional coupled static and dynamic load,and then static uniaxial state.Temperature sensibility of artificial frozen soil at high strain rate is higher compared with that under low strain rate.Meanwhile,in SHPB test,temperature sensibility of artificial frozen soil under uniaxial state is bigger compared with that under three-dimensional coupled static and dynamic load.The first and second stage deformation modulus of artificial frozen silty clay increase with the decrease of temperature,the growth value of first stage deformation modulus is larger than that of second stage deformation modulus.(4)At the same freezing temperature,dissipated energy density of artificial frozen soil under confining pressure state is higher than that under uniaxial state.At the same stress state,the dissipated energy density of artificial frozen soil increase with the increase of strain rate and the decrease of freezing temperature.At the same axial compressive stress ratio,dissipated energy density under three-dimensional coupled static and dynamic load is higher than that under one-dimensional coupled static and dynamic load.In addition,with the increase of axial compressive stress ratio,dissipated energy density of artificial frozen soil first increases and then decreases at one and three-dimensional coupled static and dynamic load.The axial compressive stress ratios corresponding to peak dissipated energy density are 0.7 and 0.8 for one and three-dimensional coupled static and dynamic load,respectively.Average fragmentation degree decreases with the increase of dissipated energy density,exhibits a logarithm correlation.(5)With the help of experimental data in confining pressure state,one and three-dimensional coupled static and dynamic load state,a dynamic constitutive model is proposed.The effects of confining pressure,axial pre-compressive stress,strain rate,freezing temperature,and frozen type on the dynamic mechanical behavior of frozen soil are well considered in these models.Theoretical and experimental results are very close and the given dynamic constitutive model is feasible.