| With the vigorous development of China's high-speed railway industry,more and more highspeed railways are built on soft foundations,and the vibration of foundations caused by high-speed train loads has attracted more and more attention.Saturated sand foundation,as a kind of soft foundation,will not only settle under the load of high-speed train,but also liquefy,which will cause a series of hazards.In this paper,a series of tests of Fujian standard sand were carried out by using GDS dynamic triaxial apparatus in laboratory to study the dynamic characteristics of saturated sand under high-speed train load.Based on the test results,the stiffness attenuation model was developed by using ABAQUS finite element software,and combined with Mohr-Coulomb constitutive model,the cumulative axial strain of saturated sand was simulated and tested.The experimental results are compared to verify the feasibility of the model.A three-dimensional finite element model of track-subgrade-foundation is established by using ABAQUS finite element software,and the dynamic response of saturated sand foundation under moving load of high-speed railway train is studied.The conclusions obtained provide theoretical basis and reference for railway design.The main research results are as follows:(1)The dynamic characteristics of saturated sand under unidirectional loading are studied experimentally,and the development laws of cumulative axial strain and dynamic pore pressure of saturated sand under different conditions,such as vibration frequency,consolidation confining pressure,consolidation method and dynamic stress amplitude,are comprehensively considered.It can be found from the tests that the dynamic characteristics of sand under eccentric consolidation are completely different from those under isobaric consolidation;the dynamic stress amplitude and confining pressure are the main factors determining the development of dynamic characteristics of saturated sand,and the cumulative axial strain and dynamic pore pressure of saturated sand increase with the increase of dynamic stress amplitude and decrease with the increase of confining pressure;when the loading frequency is low,the dynamic characteristics of sand increase with the increase of dynamic stress amplitude and dynamic pore pressure.Greater cumulative axial strain and dynamic pore pressure will occur.However,for foundation soil,it has a certain natural frequency.When the frequency of the applied moving load approaches or reaches its natural frequency,it will cause a certain degree of resonance of foundation soil,which will lead to greater cumulative axial strain and dynamic pore pressure.The natural frequency of sand measured in this test is 3.5 Hz.(2)The dynamic characteristics of saturated sand under biaxial loading are studied experimentally.The influence of confining pressure on dynamic pore pressure and cumulative axial strain of saturated sand under biaxial loading is the same whether it is biaxial vibration or unidirectional vibration.The law of development of dynamic pore pressure and cumulative axial strain of saturated sand under different phase difference is two symmetrical similar and 180 degree symmetrical.This is because the stress path of different phase difference is related to the stress path of saturated sand.The phase difference is 180 symmetrical,and 180 has the greatest influence on the cumulative strain and dynamic pore pressure of saturated sand.(3)Based on the dynamic triaxial test results,the stiffness attenuation model was developed by using ABAQUS finite element software,and combined with Mohr-Coulomb constitutive model,the cumulative axial strain of saturated sand was numerically simulated and compared with the test results.The results show that only the stable strain curve has the best simulation effect,and the failure and critical strain curves have better simulation effect in the small strain stage,but in the large strain stage,there will be larger errors,which shows that the stiffness attenuation model has some limitations.Overall,the stiffness attenuation model can be used to simulate the longterm stable deformation of sand under high-speed railway load.(4)A three-dimensional finite element model of track-subgrade-foundation is established by using ABAQUS finite element software,and the dynamic response of saturated sand foundation under moving load of high-speed railway train is studied.The results show that the dynamic stress is saddle-shaped along the transverse direction of the foundation and is symmetrical with respect to the center of the foundation.The dynamic stress decreases approximately in accordance with the exponential function curve in the foundation;the dynamic displacement in the foundation is mainly vertical,and there will be some displacement along the track direction,which deserves attention;the attenuation law of the vertical displacement along the depth of the foundation and the dynamic stress phase;and the velocity responds to the dynamic response of the foundation.With the increase of velocity,the dynamic response of foundation will show greater fluctuation;the dynamic acceleration will increase with the increase of velocity,while the relationship between dynamic stress and displacement and velocity is not positively correlated.There is a critical velocity.The relationship between dynamic stress and displacement is positively correlated with velocity before the velocity reaches the critical speed,but when the velocity exceeds the critical speed.The dynamic stress and displacement decrease with the increase of speed,and railway designers need to pay attention to the influence of vehicle-like speed near 360 km/h on the dynamic response of the foundation,because when the train speed reaches 360 km/h,the dynamic stress and displacement of the foundation will increase to a certain extent,which increases the potential safety hazards.The dynamic response of foundation under two-way train load is larger than that under one-way load on the whole,but the dynamic stress of foundation decreases faster with the depth of foundation than that under one-way load. |
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