Study On The Static And Dynamic Characteristics Of Freezing And Thawing Cement Soil In Soft Soil Under Vibration Load Of Subway

At present,the artificial freezing method is mostly used in the construction of soft soil layer communication channel.Under some special geological conditions,the artificial freezing and thawing settlement can be effectively restrained,and the secondary reinforcement can be artificially frozen after the soil-soil improvement is adopted.However,it has faced the problem of uneven settlement of large number of contact channels during subway operation.The static and dynamic characteristics of heterogeneous cement soil in soft soil after freezing and thawing are the key scientific problems to solve the problem of uneven settlement during operation.It is very important to grasp the static dynamic characteristics of the freeze-thaw of water soil to the long-term operation of subway tunnels.In this article,based on the laboratory test and theoretical analysis,the basic physical performance parameters of freeze-thaw cement soil in soft soil formation,the macroscopic dynamic characteristics of freeze-thawing cement soil in soft soil stratum under static and subway vibration loads(freezing and thawing only once)are studied.Basic physical properties,the specific gravity of cement-soil increased slightly with the increase of cement ratio,its liquid limit has hardly changed,the plastic limit changes greatly,and the soil plasticity index decreases with the increase of cement incorporation ratio.The thermal conductivity,the specific heat capacity and the coefficient of thermal conductivity are linearly related to the cement mixing ratio.The thermal conductivity and specific heat capacity are inversely proportional to the mixing ratio of cement,and the temperature coefficient is proportional to the cement incorporation ratio.Statics aspects,with the improvement of cement,the static properties of soil samples have changed greatly.With the increase of cement content,its maximum strength increased by 70%.The internal friction Angle showed exponential growth,with the maximum increase of 90%.When the cement incorporation is low,the principal stress is poor--strain curve shows strain hardening type,which shows plastic damage.When the cement incorporation ratio is greater than or equal to 3%,the principal stress-strain curve is strain softening,which is characterized by brittle failure.After one freezing-thawing,the strength of sample was decreased,and the strength loss was less than 10%.But the overall change trend is consistent with the frozen and thawed soil samples.Damage form aspect,after freezing and thawing,the specimen was subjected to shear failure and brittle tensile fracture.The crack develops along the axis,forming a plastic flow zone.It produces large axial and radial deformation,and the whole is waist drum.As the cement incorporation ratio increases,its deformation size decreases gradually.Based on the experimental data,the static constitutive model is established.The regression formula based on confining pressure and cement content as parameter variables is given,and provide theoretical basis for future engineering applications.Dynamical aspect,the effects of cement blending ratio,confining pressure,vibration frequency,cyclic stress ratio and vibration times on the dynamic strain,dynamic elastic modulus and dynamic damping of soft soil cement soil after freeze-thaw are studied and analyzed.It can be found that,the larger the mixing ratio of freeze-thaw cement soil,the smaller the hysteresis loop area in the dynamic test.It present the trend of rapid first and then slow development and its cumulative plastic strain maximum reduction is 50%.Under the same conditions,the dynamic mode decreases with the increase of vibration number.Along with the vibration frequency increases,the increase of the ratio of cement mixing linear increase.Dynamic damping ratio increases with the increase of vibration frequency or nonlinear.With the increase of vibration frequency,the cement incorporation ratio increases linearly,and there is a change critical value;macroscopically,the dynamic characteristics of soft soil cement soil are different before and after freezing and thawing.Once frozen,the intensity decreased by 6% than pre-freeze;engineering of the connecting passage surrounding formation heterogeneity and thawing soil cement content should be greater than 5%;the long-term cyclic load of subway has little effect on the dynamic characteristics of soft soil after freeze-thawing,so it can not be considered in engineering;the above research has important theoretical significance and practical value to solve the uneven settlement of soft soil during subway operation.