Study On Dynamic Characteristics Evolution Of Silt In Yellow River Flood Field Under Freeze-thaw Cycle

Frothing is the main disease of highways in Yellow River Flood Field,Shandong Province.It is essentially a manifestation of the loss of dynamic strength of roadbed soils under the combined effects of temperature,salt,and vehicle traffic load.The cause is closely related to the dynamic characteristics of the roadbed soils in Yellow River Flood Field.Yellow River Flood Field of Shandong Province is a seasonally frozen area with a relatively thick silt layer on the surface.The groundwater level in the area is shallow and the concentration of salt in the water is high.Due to the capillary action of the silt,salinization is widespread.Therefore,it is of great significance to study the influence of freeze-thaw cycle and salt on the dynamic properties of roadbed silt.In order to provide a theoretical basis for the treatment of silty soil highway roadbed in Yellow River Flood Field,Shandong,this study carries out a pressure freeze-thaw cycle test,a pressureless freeze-thaw cycle test,a vibration triaxial test,an ultrasonic test and magnetic resonance imaging scan test on salt-free soil samples and salty soil samples for in-depth analysis of the effects of salt and freeze-thaw cycles on soil dynamics and meso-structure:(1)Freeze-thaw cycles and salt will reduce the dynamic shear strength of silt,and the application of a certain axial force during the freeze-thaw cycle can improve the dynamic shear strength of the soil.The dynamic shear strength of salt-free silt after six cycles of freeze-thaw cycles is reduced by 15.7%,and the dynamic shear strength of silt with 3%salt content after six freeze-thaw cycles is 33.9%lower than that without freeze-thaw cycles;In the absence of freeze-thaw conditions,the initial dynamic shear strength of salt-free silt is about 19.6%higher than that of the silt containing 3%salt;the dynamic shear strength difference increases to about 36.9%after six freeze-thaw cycles.The dynamic shear strength of the test specimen with vertical pressure of 20kpa applied in freeze-thaw cycle is 12.1%?16.5%higher than the dynamic shear strength of the test specimen of pressureless freeze-thaw.(2)Freeze-thaw cycle and salt reduces the dynamic elastic modulus of soil samples.The dynamic elastic modulus of unsalted silt after six times of freeze-thaw cycles is about 26.7%lower than that without freeze-thaw.After six times of freeze-thaw cycles,the dynamic modulus of elasticity of silt with 3%salt content is 45.2%lower than that without freeze-thaw,the salt content enhances the degree of freeze-thaw reduction of dynamic elastic modulus;in the absence of freeze-thaw action,the dynamic elastic modulus of salt-free silt is 87.2kpa higher than that of of silt with 3%salt content,which is about 46.2%.After six freeze-thaw cycles,the dynamic elastic modulus of salt-free silt is 82.7kpa higher than that of saline-containing 3%silt,about 59.8%higher.(3)Both freeze-thaw cycle and salinity can increase the damping ratio of soil samples.After six freeze-thaw cycles,the damping ratio of salt-free silt increases by about 15.8%compared with that of non-freeze-thaw cycles.After six freezing-thawing cycles,the damping ratio of silt with 3%salt content is about 20.5%higher than that without freezing-thawing.Salt content enhances the degree of freeze-thaw to increase the damping ratio;the salt-free silt damping ratio is about 11%lower than of the silt with 3%salt content without freezing and thawing.After six cycles of freeze-thaw cycles,the damping ratio of salt-free silt is about 15.9%lower than that of the silt with 3%salt content.(4)Ultrasonic Wave Velocity of Frozen Soil Samples Decreases with freezing and thawing Times.The wave speed of salt-free silt after six cycles of freeze-thaw cycles is about 0.32m/s,about 15.5%lower than that without freeze-thaw cycles.The wave speed of silt with 3%salt content after six cycles of freeze-thaw cycles is 0.283m/s lower than that without freezing and thawing,which is about 14.3%.The wave speed of silt with 6%salt content after six cycles of freeze-thaw cycles is 0.277m/s lower than that without freezing and thawing,which is about 14.2%.In the absence of freezing and thawing,the wave speed of salt-free silt is 0.078 m/s higher than that of silt with 3%salt content,which was approximately 3.78%.After six cycles of freezing and thawing,the wave speed of salt-free silt is 0.041 m/s higher than that of silt with 3%salt content,which is about 2.3%.The wave speed of salt-free silt is 0.116 m/s higher than silt with 6%salt content,which is about 5.62%.After six cycles of freezing and thawing,the wave speed of salt-free silt is 0.073 m/s higher than that of silt with 6%salt content,which is about 4.18%.(5)Based on the above studies(1),(2),and(4),the relationship between ultrasonic wave velocity damage of frozen soil samples,DV,and dynamic shear strength damage,DE,is established and the relationship between ultrasonic wave velocity damage of frozen soil samples,DV,and dynamic elastic modulus shear damage,DE,is established.With this model,the dynamic performance damage of roadbed soil can be quickly evaluated through field measurement ultrasonic data.(6)Through MRI scanning tests,it is found that under the freeze-thaw cycle,the pores of the silt in the yellow river flood field will become larger,the skeleton will reorganize,the arrangement of the soil particles will change,the distance between the soil particles will increase,and the contact area between the particles will decrease,leading to the decrease of the interfacial contact force.shows a macroscopic change inthe dynamic characteristics of the silt in the flooded area.The macroscopicmanifestation is the change of the dynamic characteristics of silt in the yellow river flood field.