Current situation and development trend of design methods for subgrade structure of high speed railways

Purpose–This method will become a new development trend in subgrade structure design for high speed railways.Design/methodology/approach–This paper summarizes the structural types and design methods of subgrade bed for high speed railways in China,Japan,France,Germany,the United States and other countries based on the study and analysis of existing literature and combined with the research results and practices of high speed railway subgrade engineering at home and abroad.Findings–It is found that in foreign countries,the layered reinforced structure is generally adopted for the subgrade bed of high speed railways,and the unified double-layer or multi-layer structure is adopted for the surface layer of subgrade bed,while the simple structure is adopted in China;in foreign countries,different inspection parameters are adopted to evaluate the compaction state of fillers according to their respective understanding and practice,while in China,compaction coefficient,subsoil coefficient and dynamic deformation modulus are adopted for such evaluation;in foreign countries,the subgrade top deformation control method,the subgrade bottom deformation control method,the subsurface fill strength control method are mainly adopted in subgrade bed structure design of high speed railways,while in China,dynamic deformation control of subgrade surface and dynamic strain control of subgrade bed bottom layer is adopted in the design.However,the cumulative deformation of subgrade caused by train cyclic vibration load is not considered in the existing design methods.Originality/value–This paper introduces a new subgrade structure design method based on whole-process dynamics analysis that meets subgrade functional requirements and is established on the basis of the existing research at home and abroad on prediction methods for cumulative deformation of subgrade soil.

A constitutive model for cyclic densification of coarse-grained soil filler for the high-speed railway subgrade considering particle breakage

Purpose–This study aims to propose a semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the high-speed railway(HSR)subgrade under cyclic load.Design/methodology/approach–According to the basic framework of critical state soil mechanics and in view of the characteristics of the coarse-grained soil filler for the HSR subgrade to bear the train vibration load repeatedly for a long time,the hyperbolic empirical relationship between particle breakage and plastic work was derived.Considering the influence of cyclic vibration time and stress ratio,the particle breakage correction function of coarse-grained soil filler for the HSR subgrade under cyclic load was proposed.According to the classical theory of plastic mechanics,the shearing dilatation equation of the coarse-grained soil filler for the HSR subgrade considering particle breakage was modified and obtained.A semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the HSR subgrade under cyclic load was further established.The backward Euler method was used to discretize the constitutive equation,build a numerical algorithm of“elastic prediction and plastic modification”and make a secondary development of the program to solve the cyclic compaction model.Findings–Through the comparison with the result of laboratory triaxial test under the cyclic loading of coarse-grained soil filler for the HSR subgrade,the accuracy and applicability of the cyclic compaction model were verified.Results show that the model can accurately predict the cumulative deformation characteristics of coarse-grained soil filler for the HSR subgrade under the train vibration loading repeatedly for a long time.It considers the effects of particle breakage and stress ratio,which can be used to calculate and analyze the stress and deformation evolution law of the subgrade structure for HSR.