Study On The Deformation And Particle Crushing Evolution Characteristics Of Coarse-grained Soil In Railway Subgrade

Railway subgrade is subjected to the load,which including the self-weight of fill,static load of track structure and dynamic load of train,and its deformation is derived from dynamic accumulation and creep deformation,the essential reason of which is coarse particle breakage and fine particle migration of filler.At present,its deformation characteristics are extremely complex owing to the special composition of coarse-grained soil,and because of the limitation of experimental conditions and the complexity of problems,the research in this field is superfical without revealing the deformation mechanism of coarse-grained soil subgrade in depth.Therefore,it is necessary to investigate deeply on the dynamic cumulative deformation characteristics and creep of coarse-grained soil filler.This research constructs a coarse-grained soil model test system with carring out dynamic cyclic loading and creep tests of coarse-grained soil under static and dynamic loads,explores the dynamic and static deformation characteristics of coarse-grained soil fillers,and reveals the deformational mechanism from the perspective of particle’s breakage.The specific researches and conclusions are as follows:(1)In order to describe the grading characteristics of coarse-grained soil,the nonlinear relationship between particle content p and relative particle size x natural logarithm is established by using quadratic function,and a grading equation describing continuous graded coarse-grained soil is proposed in the coordinate system of particle content and relative particle size.The grading curve of discontinuous graded coarse-grained soil is discretized into local continuous grading curve,and the grading equation of discontinuous graded coarse-grained soil is constructed on the basis of continuous grading equation through coordinate transformation,which verifies the applicability of the equation.(2)This research constructs a dynamic cyclic loading model test system of coarse-grained soil filler,revealing the dynamic cumulative deformation characteristics of it under the long term reciprocating load of high-speed trains.The MTS was used to simulate the dynamic loads of train with different frequencies and different dynamic stresses,and 50,000 cyclic loading tests were carried out,and the relationship curve between dynamic cumulative strain and loading times of coarse-grained soil filler was obtained.The influence of loading frequency,dynamic stress amplitude,rainfall infiltration intensity and other factors on cumulative strain is deeply analyzed.An exponential hyperbolic function prediction model for dynamic cumulative strain and loading times of coarse-grained soil filler is proposed,and the functional relationship between model parameters and the frequency of loading,dynamic stress amplitude and rainfall infiltration amount is established.The rationality of the model is verified by experimental data.(3)In order to reveal the creep deformation characteristics of subgrade coarse-grained filler soil,a system of creep model for coarse-grained soil is established with creep tests,discussing the effects of static pressure load,rainfall infiltration degree,compactness and lateral stiffness.The results showed that the static pressure deformation increased linearly with adding load,while the creep deformation increased exponentially with the load and time,and the slope of fuction gradually decreased until it stabilized.The final deformation of static pressure changes slightly with augmenting rainfall infiltration,its tendency drops gradually with the increase of lateral limit and compactness;creep deformation tends to be stable after 48 hours,and its final deformation increases with the amount of rainfall infiltration and decreases with enlarging lateral stiffness and compactness.(4)Analyzing the distribution of the particle of the coares-grained size before and after test,discussing the particle crushing characteristics of it under load,this research reveals the deformation mechanism of it.The results show that the fracture of large particles and the grinding effect of small particles increase obviously due to the increase of dynamic stress amplitude,loading frequency and rainfall infiltration amount.Particle crushing is more remarkable with compaction degree and lateral stiffness increasingly.The results show that the particle size distribution of coarse-grained soil filler after crushing has good fractal characteristics with a good linear relationship between fractal dimension D and particle crushing index B_g.