Research On The Static And Dynamic Characteristics Of Silty Clay And The Settlement Law Of Subgrade Of High-speed Railway

The embankment static load and the long cycle vibration load of high-speed train load will lead the strength of foundation soil decreasing and the plastic strain accumulating. And then cause the inhomogeneous deformation even result in the foundation instability. This will bring a lot of hidden security trouble during the normal operation of high speed railway. Therefore, the static and dynamic characteristic tests research on the saturation silty clay under complex stress path is very necessary and the above research results will provide an important reference for disaster control technology of high-speed railway subgrade.To counter the above issues, this paper mainly finished the following work by using GDS triaxial apparatus GDS and hollow cylinder apparatus.(1) The consolidated drained triaxial test, the directional shear triaxial test of the K0 consolidation saturated silty clay under different stress state and principal stress direction angle are carried out by using the GDS triaxial test system according to the real static load state of subgrade soil under the embankment load. The mechanical properties and deformation characteristics of the K0 consolidation saturated silty clay are researched and structural mathematical model which import stress ratio structural parameters and structural loss are established. The stress path slope influence on the K0 consolidation saturated silty clay is analyzed. The stress vs. strain development law and the non-coaxial phenomenon of K0 consolidation saturated silty clay under different direction angle between the principal stress and the vertical direction is revealed. The strength envelope on the τZθ/σc0～(σz-σθ)/2σc0 plan is proposed.(2) The dynamic tests of silty clay under different test conditions which vibration numbers equal to 10000 times are carried out by using the DDS-70 dynamic triaxial apparatus. And the strain failure criterion of silty clay is discussed. The curves between the dynamic stress(σd) and dynamic strain(εc) under high-speed train load are obtained. The dynamic constitutive relation experience formula of silty clay under the long term high-speed train load is also established. The influence factors, such as moisture contents, consolidation ratio, vibration frequency, static deviatoric stress, consolidation confining pressure and the amplitude of dynamic stress, impact on the dynamic characteristic of silty clay are researched. The normalization formula of the maximum dynamic modulus of elasticity and the maximum dynamic damping ratio of the silty clay are proposed.(3) The dynamic characteristic research on saturated silty clay under variable confining stress path are carried out according to the characteristics of subgrade soil which both the vertical and the horizontal stress cyclic changes when it bears the high-speed train load. The regularity of pore pressure, the axial strain and volume strain of silty clay both in undrained and partial drained conditions are researched according to the variable confining pressure cycle triaxial tests both in undrained conditions and partial drained conditions. The settlement prediction model of silty clay under variable confining pressure conditions is also established.(4) The cyclic triaxial tests and cyclic torsional shear tests of K0 consolidation saturated silty clay under different cyclic dynamic stress ratio and dynamic stress path are carried out by using the GDS-HCA test system according to the occurrence of principal stress axes rotation continuous of subgrade soil under high-speed train load. The principal stress direction continuous cyclic rotation influence on the accumulative plastic strain and pore pressure characteristics of K0 consolidation saturated silty clay are researched. And the accumulated plastic strain equation of K0 consolidation saturated silty clay under the principal stress direction continuous cyclic rotation conditions is established.(5) The subgrade cross section form in DK 599+720m of Beijing to Shenyang passenger dedicated line are taken as the research object. The three-dimensional dynamic elastic-plastic numerical calculation model is established by using the finite element analysis software MIDAS/GTS. The long term subgrade settlement regularity and mechanism under the high-speed train load are analyzed according to the numerical simulation results. The subgrade long-term settlement under the high-speed train load is scientific predicted by respectively using hyperbolic prediction method, exponential curve forecasting method and grey system GM (1,1) model. And then evaluate the accuracy of the three above predict methods according to the comparison of the numerical simulation results and predict results.