Study On Long-Term Dynamic Characteristics Of Soft Clay Under Cyclic Traffic Load

The soft clay is widely distributed in our country.With the rapid development of our transportation,the foundation settlement problem caused by the movement of traffic engineering is more prominent.Long-term cyclic load will not only affect the smoothness of the pavement and the service life of the road in soft soil foundation,but also bring cumulative settlement and hidden safety risks.Therefore,it is very important to study the dynamic characteristics of soft clay under traffic cyclic load to effectively predict and control the settlement of soft soil foundation.Taking Taizhou Marine soft clay as the research object,a series of cyclic triaxial tests and static shear triaxial tests are carried out,and the bending element tests are carried out on the soft clay before and after the cyclic load,and the mechanism of soil deformation under cyclic load is proposed.Finally,an improved HCA model of clay is established based on simulated annealing algorithm.The main research work and related achievements are as follows:（1）A series of undrained cyclic shear tests were carried out on soft clay to study the evolution law of cumulative axial deformation,cumulative pore pressure and resilience modulus of clay under different traffic cyclic loads including dynamic stress ratio,initial average effective stress,initial pore ratio,clay anisotropy during initial consolidation,stress anisotropy generated by engineering pile preloading and consolidation ratio.The change of shear modulus of soil before and after the cycle is compared.The results show that the larger the cyclic load dynamic stress ratio,initial average effective stress,initial pore ratio and initial consolidation anisotropy,the larger the axial cumulative deformation and cumulative pore pressure,and the smaller the rebound modulus.However,the stress anisotropy and consolidation ratio produced by loading are opposite.The shear wave velocity and shear modulus of the clay decrease after cyclic loading is applied.After vibration,the shear modulus decreases with the increase of dynamic stress ratio of load,but the frequency has little effect on the shear modulus.（2）The long-term dynamic characteristics of soft soil under different stress paths of constant confining pressure（CCP）and variable confining pressure（VCP）were investigated by carrying out dynamic triaxial bidirectional cyclic tests.η^ampl is defined as the ratio of cyclic mean effective stress amplitude to cyclic deviatoric stress amplitude in biaxial cyclic triaxial samples.The results show that when the cyclic stress ratio is small,the final axial cumulative strain is positively correlated withη^ampl,and the resilience modulus of CCP under cyclic loading is higher than that of VCP.However,with the increase of dynamic stress ratio under cyclic loading,the increase ofη^amplsignificantly reduces the axial cumulative strain of soil samples with the increase of radial constraint under cyclic confining pressure,and the softening of soil samples under CCP condition becomes more significant.（3）Through the unidirectional cycle triaxial undrained test,the influence of frequency on the dynamic characteristics of soft clay under long-term cyclic load is emphatically explored,and the relevant mechanism of action is clarified.The results show that at low cyclic stress ratio,the higher the frequency of soft clay,the greater the axial cumulative deformation and pore pressure,and the smaller the springback modulus of the sample.When the dynamic stress ratio is too large,the soft clay samples show the opposite rule.According to the above rules,it is proposed that the deformation of soft clay is affected by the frequency-generated energy and the hysteresis effect under different frequency traffic cycle loads.According to the results of the undrained cycle test,it is believed that the energy absorbed by the soil particles during the vibration process leads to the transformation of the strong and weak water adsorbed on the surface,resulting in the weakening of the soil mass.（4）Based on the dynamic triaxial test data of GDS,the calculation formula of frequency function and volume modulus K is improved on the basis of the original HCA model,and an improved HCA clay model considering the influence of frequency is established to increase the model universality and prediction accuracy.A calibration method using simulated annealing algorithm is proposed,and the reliability of the model is verified by comparing the predicted values with the measured values.The results show that the improved HCA model can predict the strain and pore pressure under long-term cyclic loading.