Study On Long-Term Dynamic Stability Of High Speed Railway Lime-Improvement Loess Subgrade Under Cyclic Load

With the development of high-speed railway,the speed of trains and the traffic volume increases,the dynamic load of roadbed also increases,and the settlement of roadbed will directly affect the safe operation of trains.In order to save the transportation cost and engineering cost of the high quality fillers,lime and other hardener can be used to improve the loess,so that the range of the loess can be expanded.Because of the use of lime technology started relatively late in China construction of railway subgrade,especially on long-term dynamic stability of high-speed railway subgrade with lime under cyclic load.It is necessary to carry out an in-depth study on it.In this paper,under the project of the National Natural Science Fund the loess of Lanzhou area was chemically improved.The mechanical response and dynamic stability of lime modified loess under train load are studied systematically.So draw the following conclusions:(1)By means of physical and mechanical properties test,unconfined compressive strength test and indoor static tri-axial test,the improved physical and mechanical indexes of loess with different lime adulteration(5%,6%,8%)are obtained,and the relationship between unbounded compressive strength and shear strength of lime modified loess and lime admixture is discussed.(2)The dynamic constitutive relationship and dynamic modulus characteristics of lime-modified loess under different test conditions were studied by the British GDS dynamic tri-axial instrument,and the influence laws of surrounding pressure and consolidation ratio were discussed.By analyzing the experimental data,the constitutive relation of lime modified loess was described by using R.L.Kondner hyperbolic model,and the parameters of the model were obtained.The maximum elastic modulus increases with the increase of the ratio of encirclement and consolidation.(3)Using the three-axis test technique of stress control system for short time and fatigue labor,three modified loess shear strain thresholds for short time and fatigue labor under different test conditions were obtained.The effects of lime addition,surrounding pressure and consolidation ratio are discussed,and the empirical formula of short-time dynamic shear and fatigue shear are obtained by regression analysis.The correlation is obtained by data comparison analysis.(4)Studying the change characteristics of the cumulative plastic strain with the change curve,obtain the change law of the critical dynamic stress of the lime-modified loess under different factors,and analyze the relation formula of the critical dynamic stress,which can provide better stability parameters for evaluating the dynamic stability of lime-modified loess;The relationship between the unconfined compressive strength and the threshold of dynamicshear strain is established,and the threshold value of dynamic shear strain can be obtained by a simple test.(5)Based on the simulation of lime modified loess base value,the dynamic stability of lime modified loess road was evaluated by dynamic shear stress method and critical dynamic stress method.By contrast,the dynamic shear strain method can be used to evaluate the dynamic stability of lime modified loess base.