Research On Mechanical Properties And Constitutive Relationship Of Bank Soil Of The Yellow River Under Freezing And Thawing

The embankment is an important barrier for the river flood control system.The Yellow River(Inner Mongolia section)experiences a freezing-thawing process from winter to spring every year,which is a typical seasonal frozen soil area.The entire bank soil on both sides of the river can be classified as loose river deposits in the fourth quarter.After being repeatedly subjected to the seasonal freezing-thawing process every year,the grain structure,mechanical properties and strength characteristics of the bank soil will be greatly affected.Changes,and these microscopic changes in the soil structure,combined with the erosion of the bank slope by the river during the flood season,will often accelerate the destruction of the bank slope,triggering the collapse of the river bank,raising the river bed,and threatening the lives and property of the people outside the bank.Therefore,based on the influence of the freezing and thawing process on the bank slope,the mechanical characteristic test of the soil of the Yellow River bank under the freezing and thawing cycle conditions is important for the analysis of the collapse mechanism mode of the bank in the seasonal freezing area,the evolution of the river and the protection of the bank safety.significance.Based on the influence of freeze-thaw erosion on the embankment soil,this thesis carried out a triaxial consolidation undrained shear test under different water content,freeze-thaw cycles and confining pressure,and analyzed the soil stress of the Yellow River embankment based on the test data-The constitutive relationship of the strain curve provides important theoretical support for investigating the changes in the mechanical properties of the embankment soil of the Inner Mongolia section of the Yellow River in the seasonal freezing area with the number of freeze-thaw cycles,the mechanism model of embankment collapse,and the protection of embankment safety.The results obtained are as follows:(1)When the moisture content of the soil sample is greater than or equal to the optimal moisture content,the stress-strain relationship curve of the unfreeze-thaw soil sample is strain-hardening,and becomes strain-stable after different times of freeze-thaw cycles,but under high confining pressure In the shearing process,the stress-strain curve of the sample will show weak softening characteristics,and as the number of freeze-thaw cycles increases,the softening degree becomes more obvious;when the moisture content of the soil sample is lower than the optimal moisture content,the stress-strain curve After the peak,the softening characteristics are remarkable.The cohesive force of soil samples varies greatly under different freezing and thawing times,but the internal friction angle is less affected by the effects of freezing and thawing.Therefore,the changes in the shear strength of the soil on the banks of the Yellow River under freezing and thawing conditions are mainly reflected in the cohesion of the soil.Under different water content,the largest decrease in cohesion occurs after the first freeze-thaw cycle.(2)According to the hyperbolic equation proposed by Kondner and the model of Nanjing Institute of Hydraulic Research,the stress-strain relationship curve of embankment silt with different moisture content and different freeze-thaw cycles was analyzed and predicted,and the Duncan-Chang model was used to analyze embankment soil.The physical parameters in the body constitutive relationship have been revised.The results show that the normalized equation established based on the triaxial test data and the improved South Water Model of the embankment soil can better predict the stress-strain relationship of the sample under different freeze-thaw cycles,and the calculated value is close to the measured value.(3)Based on the actual measured value of the Yellow River embankment soil in the triaxial test and the model predicted value,according to the limit equilibrium law,the measured change curve of the embankment stability safety factor during the freeze-thaw cycle and the model prediction curve are obtained,and the curve shows that the freeze-thaw erosion The effect will significantly reduce the mechanical properties of the beachfront soil,thereby reducing the stability of the beachfront.At the same time,the predicted curve of the model obtained is similar to the measured curve,and the predicted value is smaller than the measured value,which is safer in engineering applications.