Study On Stress Wave Propagation Characteristics Of The Sandwiched Coarse Praticle Struture Of Embedded Pile-Board Subgrade

With the continuous development of high-speed railway, to ensure its safety and comfort, subgrade needs to provide steady and smooth base as substructure.In some deep soft soil area, the form of embedded pile-board structure subgrade is put forward to meet the post-constructon settlement and driving requirement of high-speed train.The embedded pile-board structure subgrade as multi-layer complicated structure,where the coarse particles sandwiched by rail structure and pile-board structure and pile-board structure was embedded into the foundation bearing upper loads,forms the upper rigity-the middle flexibility-the lower rigity structure system. Sandwiched coarse particles structure under stress conditions is quite complicated, considering the stress wave caused by train loads reflection and refraction at track structure/sandwiched coarse particles/pile-board structure interfaces. Therefore, sandwiched coarse particles structure as a weak interlayer there in no doubt that study on its stress wave propagation characteristic and dynamic interaction mechanism is necessary.In this paper, slab ballastless track and pile-board are elastic or viscoelastic medium, while the andwiched coarse particles as a saturated porous medium.Based on the elastic wave theory and the Biot theory, introducing scalar potential functions, reflection and refraction of stress wave at track structure/sandwiched coarse particles/pile-board structure interfaces through the governing equation and boundary conditions were derived.Using a numerical examples by matlab program, the reflection and refration coefficients with varying sandwiched coarse particles depths,incident angles,excitation frequencies and permeability coefficents are discussed, in addition, the attenuation of wave and damage energy dissipation are analyzed with some original opinions.At last, the calculating program were checked by Comsol finite element analysis under specific conditions on reflection coefficients.The result as follows(1) Researching the theory and method about stress wave propagation in porous medium, introducting stress characteristic and complexity of sandwiched coarse particles for embedded pile-board structure subgrade, pointing out the scientific question concerning to wave propagation in sandwiched coarse particles providing the basis for study in this paper.(2) P wave and SV wave velocity are no relation with frequency in elastic medium,while have dispersion characteristic in viscoelastic medium.According to Biot theory and Stokes-Helmholtz theory, the fundamental solutions for the coupled body wave(P1 wave,P2 wave,SV wave) were set up as well as the characteristic equation and the amplitude ratio of solid-liquid phase were derived.The body wave propagation characteristic in porous medium varying with porosity,excitation frequencies are discussed.The result show that the fluid phase has great effect on the wave propagation.(3) Slab ballastless track structure-sandwiched coarse particles-pile-board structure model was proposed, matrix equation of reflection and refraction of stress wave was derived. The result as follows:due to the sandwiche coarse particles depth and porosity variation,the natural frequencies of sandwiched coarse particles layer varies. Therefore, the amplitude of the reflection and refraction coefficient varies periodically along the sandwiche coarse particles depth and porosity.The high excitation frequency results in high attenuation of the sandwiched coarse particles. There is no critical angle of the sandwiched layer varying with different incidence angles attributed to the energy loss in the sandewiched coarse particles. However, mainly affects transformation of wave type.The overall attenuation in the sandwiched coarse particles is composed of the energy dissipation in the skeletal frame and the viscous loss in the pore fluid. The effect of the permeability is insignificant at a low frequency.However, demonstrates the clear differences at a high frequency. The energy dissipation in the skeletal frame mainly affects the propagation of the shear wave in the sandwiched coarse particles.