| With the deepening of China’s "Western Development" and the implementation of the national strategy of "high-quality development of the Yellow River Basin",the construction of transport infrastructure in the Loess Plateau has accelerated.The special engineering geological properties of loess(water sensitivity and structural)and the topography of loess hills and gullies have brought many challenges to high-speed railway and other transportation construction in the loess plateau area.Especially the risk of subgrade settlement in loess filling area is relatively high,which seriously threatens the construction and safe operation of high-speed railway.Therefore,conducting research on the mechanical properties of loess,settlement,and dynamic response of high-speed railway subgrade in the loess filling area under rainfall has important theoretical and practical significance.This paper relies on a project funded by the Shaanxi Provincial High-speed Railway Geological Subgrade Innovation Team,and takes the high-speed railway subgrade crossing the gully filling area in the Luochuan section of the Xi’an-Yan’ an high-speed railway as the background to conduct laboratory test and numerical analysis research.The strength and deformation characteristics of foundation soil(undisturbed loess,compacted loess)and embankment(cement loess)were studied by conventional triaxial test.The microstructure and pore characteristics of undisturbed loess and compacted loess were analyzed by scanning electron microscope(SEM).Then,the dynamic characteristics of undisturbed loess,compacted loess,and cement loess were studied through dynamic triaxial tests.On this basis,a finite element model was established to study the settlement and dynamic response of highspeed railway subgrade crossing the filling areas.Obtained the following main research results.(1)Based on conventional triaxial test and SEM,the stress-strain relationship,shear strength,and microstructure changes of undisturbed loess,compacted loess,and cement loess were elucidated.The differences in critical state lines(CSL)of different types of loess were clarified,and the influence of dry density and cement content on the elastic parameters and strength parameters of loess was revealed.The influence of stress history on deformation curve of undisturbed loess cannot be ignored.As the confining pressure increases,the deformation curve transitions from strain hardening to strain softening.(2)Based on dynamic triaxial tests,the accumulated deformation,dynamic modulus,and damping ratio of three types of loess were elucidated.The accumulated deformation and dynamic modulus of undisturbed loess under over-consolidation and under-consolidation states were clarified,and the influence of different water content and cement content on the dynamic modulus of compacted loess and cement loess was revealed.Undisturbed loess has good dynamic stability,and its dynamic parameters are superior to compacted loess.(3)Based on numerical simulation calculations,the characteristics of initial settlement,settlement after rainfall of subgrade and the dynamic response of subgrade under train dynamic loads with different filling interface slopes were revealed.The range of dynamic influence depth in the filling area has been determined.The difference in soil properties at the filling interface can lead to fluctuations in dynamic response at the interface.The slope of the fill area interface should not exceed 30°. |
