Study On Dynamics Characteristics Of Expansive Soil Under Freezing And Thawing Cycle

There is a wide distribution of expansive soil along the railway in seasonally frozen region in China.Under the conditions of high cold and deep season freeze-thaw environment and the site with abundant shallow groundwater,the freeze-thaw cycle of expansive soil slope becomes the most direct cause that seriously affects the stability of the slope and induces landslides.In this paper,the expansive soil in the yanji section of JI-TU-HUN high-speed railway is taken as the research object,and the variation law of the physical and mechanical properties of expansive soil under the freezing and thawing cycle is taken as the research content.The variation law of shear strength with freeze-thaw cycle;The dynamic characteristics of expansive soil change with freeze-thaw cycle under different stress states.The dynamic characteristics of reinforced expansive soil with freeze-thaw cycle and the dynamic characteristics and accumulated deformation of reinforced expansive soil during cyclic shear were studied.The main contents and conclusions of the paper are as follows:The analysis of X-ray diffraction results combined with a series of experiments verified the composition and ratio of artificially configured expansive soils.It is:bentonite 70%,albite 17.1%,quartz 12.9%.The shear strength of both the artificially prepared soil and the in-situ soil decreases with the increase in the number of freeze-thaw cycles,and the strength characteristics are consistent.Compared with the in-situ soil,the artificially-prepared soil has a lower rate of decrease in the internal friction angle with increasing number of cycles,and the cohesive force has a higher rate of decline with increasing number of cycles.The dynamic triaxial test is used to change the dynamic shear modulus and damping ratio of expansive soil in slope under freeze-thaw cycle.,the temperature-controlled dynamic triaxial test of expansive soil was carried out under the condition of that confining pressure?₃=10,50kPa and anisotropic consolidated ratio K_c=1.25,2.0.The results show that the dynamic characteristics of expansive soil on slope under freeze-thaw cycles will vary significantly with the stress condition.Freeze-thaw cycles cause consolidation of expansive soil under confining pressure,which will increase the dynamic shear modulus G_d and decrease the damping ratio?.In a single freeze-thaw cycle,G_dmaxmax will increase by a maximum of 27.6%and the?_maxax decreased by 7.6%,this is different from the traditional understanding of soil structure damage theory of frozen swell and melt settlement.Under the action of deviatoric stress,the freezing-thawing cycle will cause additional shear deformation of the expansive soil,thereby increasing the dynamic shear modulus of the soil.The conclusions of the study further enriched the theory of dynamic characteristics of expansive soil in the slope under freeze-thaw cycles,and provided a theoretical basis for optimizing the slope treatment of expansive soil in the future.Dynamic response of reinforced expansive soil under freeze-thaw cycle was studied by dynamic triaxial test,the geogrid was used as the reinforced material,and the temperature-controlled dynamic triaxial test of the reinforced expansive soil sample was carried out.The displacement and kinetic parameters were compared with the unreinforced expansive soil samples,and the effects of freeze-thaw cycles on the soil dynamics were discussed.The results show that the dynamic shear modulus and damping ratio of the expansive soil samples are improved by reinforcement.Under the condition of?₃=50 kPa,the freeze-thaw cycle will reorganize the arrangement of the expansive soil particles and re-consolidate,which will increase the dynamic shear modulus of the soil.Reinforcement can inhibit the axial compression of the sample,and can also restrain the frost heave deformation of the sample during the freezing process,delay the structural damage effect caused by frost heave,and reduce the rate of change of the dynamic shear modulus and the damping ratio with the freeze-thaw cycle.Under the condition of?₃=10 kPa,the freeze-thaw cycle will cause expansion and deformation of the expansive soil,which will reduce the dynamic shear modulus G_d of the soil.Reinforcement can inhibit the axial expansion of the sample,reduce the rate of reduction of the dynamic shear modulus after the freeze-thaw cycle,and stabilize it more quickly,and reduce the influence of the freeze-thaw cycle on the damping ratio of the expansive soil sample.Under the two stress states,the reinforced expansive soil sample with the increase of dynamic strain,the energy consumption effect of the reinforced material is more prominent,showing that the damping ratio of the reinforced specimen is higher than that of the unreinforced specimen.