Study On Dynamic Mechanics Characteristics Of Freeze-thaw Cyclic Soil-structure Interface

With the increase of engineering projects in frozen soil area and the application of freezing method,more and more attention has been paid to the threat brought by the repeated freeze-thaw of soil layer,earthquake,train and other dynamic load effects.Therefore,it is of great significance for the construction and safe operation of frozen soil engineering to actively carry out the dynamic mechanics research of freeze-thaw soil-structure interface under corresponding engineering geological conditions.On the basis of summarizing the existing power device,the new dynamic test apparatus was designed and developed,and its applicability was verified.By the research methods combined with laboratory tests and theoretical analysis,this study conducted systematic researches on the dynamic characteristic influence factors of freeze-thaw soil-structure interface and the mutual influence between these factors.Firstly,the parameters of soil dynamic mechanics test are designed.Then,based on the conventional strain-control direct shear apparatus system and dynamic parameters designed by tests,high-performance HEV vibration exciter were employed as horizontal dynamic load applying device,corresponding control and acquisition systems were matched,the layout of each system was determined and the dynamic stress direct shear system(DSDS-1)was developed successfully.The test indexes such as shear displacement and stress were measured dynamically,and the system debugging and reliability verification were completed.On the DSDS-1 instrument,different test conditions,such as vertical pressure,freezethaw cycles(FTC),dynamic load frequency and structural surface roughness,were taken into account to carry out the experimental study on the dynamic mechanical characteristics of the freeze-thaw soil-structure interface.Results of the tests indicates that the dynamic stress-strain curves can be divided into three prominent stages which are the linear increasing stage,the rapidly increasing stage and the exponential rapidly increasing stage.The stress-strain relationship indicates strain hardening under different test conditions,the effect of normal pressure is the largest,followed by roughness of structure surface and dynamic load frequency,and the effect of freeze-thaw cycles is not obvious.The dynamic strength increased with the increase of the normal pressure.The shear strength of the interface between soil and structure was minimum with FTC of 3.The dynamic loading influenced the strength of interface between soil and structure under freeze-thaw condition far more than static loading.The roughness of structural plane influenced dynamic strength mainly by the dynamic cohesion of soil,while the dynamic cohesion was stronger with coarser structural plane.The maximum shear shrinkage of freeze-thaw soil-structure interface is affected by test conditions.The larger the normal pressure is,the lower the FTC value is,the lower the dynamic load frequency is,the coarser the structure surface is and the corresponding shear shrinkage is larger.The dynamic shear modulus ration presented a declined trend under different test conditions.The corresponding dynamic shear modulus was larger with higher normal pressure,lower dynamic frequency and less coarseness,and FTC had little influence on dynamic shear modulus.The damping ratio increased with increasing shear strain and larger normal pressure,while FTC had less influence.Moreover,the damping ratio changed when the dynamic loading frequency varied.The corresponding range of damping ratio was 0.10 to 0.14 under 2Hz,0.15 to 0.17 under 1Hz,and 0.16 to 0.20 under 0.5Hz.The damping ratio presented integral increasing trend with structural of larger coarseness.In this study,based on the researches on dynamic characteristic of the interface between soil and structure under freeze-thaw condition,advantages and disadvantages of the hyperbolic curve model and the exponential curve model were analyzed.Then,based on the statistical damage model of interface between soil and structure under freeze-thaw condition provided by Weibull distribution,applicability of the model to the interface was discussed.Finally,the concept of average relative error(ARE)was introduced to compare the fitting effects of the three models.Results of the researched indicated that the damage model performed the best fitting effects and can reflect the stress-strain relationship curves of the interface between soil-structure under freeze-thaw condition better with value of ARE less than the hyperbolic curve model and the exponential curve model.