Research On Deterioration Mechanism And Status Assessment Of Subgrade Bed On Heavy Haul Railway

Heavy haul railway transportation has widely valued in the world because of its large transport capacity,high efficiency and low transportation cost.Long-distance and large-volume cargo transportation demand is strong because of its massive land,rich in minerals resources and maldistribution in our country.The development of heavy-haul railways is an inevitable requirement for the efficient transportation of bulk materials and important symbol of railway freight modernization.In order to ensure the normal operation of the heavy haul railway,the subgrade,as the foundation of the track structure,must have the characteristics of high strength,high rigidity,good stability and durability.Due to the limitations of initial construction standards and technical conditions,as well as the increasing axle load,composition,and total freight volume of trains,which has far exceeded the design limit values,the existing heavy haul railway roadbeds have a wide range of deterioration problems,such as insufficient bearing capacity and multiple types of diseases in China.Coarse grained soil,as the main subgrade filling material,continuously undergoes particle breakage under long-term high loads,leading to significant changes in its grading and internal composition.On a macro level,it affects its physical and mechanical properties such as shear strength,permeability coefficient,and shear dilation,causing varying degrees of deterioration of heavy haul railway subgrade.However,there is currently little research on its deterioration mechanism.Therefore,research on the deterioration law of coarse-grained soil particles and the complex mechanism of subgrade degradation in-depth has become a key issue that urgently needs to be solved.This paper,based on the latest research results of testing and strengthening technology of heavy-haul railway subgrade at home and abroad,takes the Daqin heavy haul railway subgrade as the research object.Taking the degradation mechanism and state assessment of subgrade bed on heavy-haul railway as the research goal,using research methods such as field test,laboratory test,theoretical analysis,numerical simulation and evaluation theory,analyze the static and dynamic strength and deformation characteristics of the subgrade soil,study the internal deterioration mechanism of the subgrade soil,and summarize the scientific and effective evaluation methods for subgrade state.The main research contents and results of this paper are as follows:（1）Three typical sections of road-bridge transition and main track subgrade on Daqin heavy-haul railway are selected for field test.test items include K₃₀、E_v2、E_vdand degree of compaction and so on;Research the internal relationship between various parameters and evaluate the status of each subgrade with a single index;Research the variation law of dynamic stress and dynamic displacement along the horizontal,lengthways and depth directions of subgrade;The geological radar detection of different locations,different depths and different types of roadbed diseases is judged and explained.（2）The relative crushing rate B_r is proposed as the evaluation index of particle crushing degree;Study on the effect of different gradation,confining pressure and shear deformation on particle breakage of coarse-grained soil samples and its fractal breakage law.Established the relationship of fractal dimension,confining pressure and breakage rate;Investigate the evolution law of gradation,strength and deformation of coarse-grained soil based on triaxial shear test.The influence of particle crushing on peak internal friction angle,plastic work and deformation characteristics was discussed,and the influence mechanism of particle crushing on the deterioration of subgrade bed was analyzed in depth.（3）Constructing a constitutive model considering deterioration of carse-grained soil based on incremental plasticity theory;Study on the yield criterion,the flow rule and elastic-plastic modulus matrix of elastic-plastic constitutive model;Derive the elastic law,elastic-plastic strain increment,dilatancy equation,hardening criterion and constitutive equation considering the deterioration of coarse-grained soil.（4）Introduce the deterioration of carse-grained soil into conventional elastic-plastic constitutive models;Utilize the developed program to study the effects of strength and deformation characteristics for the samples under different degree of breakage,different parent rock strength,and different intermediate principal stress coefficients.（5）The evaluation index system of the subgrade condition of the heavy-haul railway is proposed,and the disease grade of the subgrade is divided.The combined analysis of analytic hierarchy process and fuzzy evaluation is used to evaluate the state of the typical railway subgrade comprehensively.The research in this paper can provide reliable theoretical and technical support for the design,construction,operation and maintenance of heavy-haul railway subgrade.