The Research Of Settlement Characteristics Of Bridge Pile Foundation Considering Creep Effect Of Soft Soil

In many bridge projects in the coastal area,soft soil layers with very obvious rheological characteristics such as silt or muddy soil are frequently encountered.However,the existing bridge foundation design methods in China generally only pay attention to short-term bearing performance but neglect the long-term effect of soft soil on foundations.It has an adverse effect on the structure durability of the project.Therefore,the appropriate creep constitutive model is selected and its model parameters are determined.The study of the rheological properties of the silt and the consideration of the foundation settlement time effect have guiding significance for the current pile foundation design.This paper relies on the subject of pile foundation in Ping Chang section of Yong Tai Wen double track of Wenzhou,Zhejiang Province.The experimental study on the silt of its consolidation-drained triaxial shear test and consolidation-drained triaxial creep test is presented in this paper.Based on the finite element analysis software Plaxis 3D of geotechnical engineering,a numerical model for the typical bridge piles under long-term surface loading was established.The long-term bearing capacity evolution of pile foundations was analyzed based on the soft soil creep model.In conclusion,the main researches are as follows:(1)Through the consolidation-drained triaxial shear test of silt,its strength,axial deformation and volume change characteristics were analyzed to determine its conventional physical and mechanical parameters.(2)The consolidation-drained triaxial creep test is completed by using separate loading methods,and the law of changes of the axial strain-time curve,volumetric strain-time curve and stress-strain isochronous curve are analyzed and studied.Under the drainage condition,the stress-strain isochronal curve of the soil sample has no obvious yield point,and the deformation of the soil sample is mainly linear viscoelastic creep deformation.(3)Based on the consolidation-drained triaxial creep test results,four commonly used creep models of Merchant model,Burgers model,power function model and Singh-Mitchell model were used to identify the parameters of the test results,the corresponding parameters of these models were determined,and the differences between these model calculation results and test results were analyzed and compared.The results show that the calculation results of the Burgers model agree well with the experimental results.(4)Using the finite element software PLAXIS,a typical model of numerical calculation for bridge piles under heaped load is established using the soft soil creep model.The time effect,the creep parameters of the silt,the thickness of the mud layer and the heaped load on the pile were analyzed for the impact of the pile axial force,the pile side friction resistance and the settlement of pile top.The results show that the maximum axial force of the pile and the settlement of the pile top increase with time,the percentage of the maximum axial force increment of the pile is 38;the change of the modified compression factor~*and the modified creep coefficient~*has a significant effect on the axial force of the pile,friction resistance of the pile side and the settlement of the pile top.Under the action of heap loading,the increase of the thickness of silt layer,the increase of the surcharge and the increase of the surcharge range all lead to the increase of the settlement of the pile top.