Study On Dynamic Characteristics And Design Methodology Of Heavy-Haul Railway Tunnel Structure

Heavy haul railway of freight transport has become the major development direction of China's railway transportation.Heavy-haul railway transportation is featured with large axle,gross weight,traffic density and traffic volume.Tunnels take up a high ratio in the whole length of a heavy-haul railway.Structural dynamic characteristics and fatigue damage caused by the heavy load and the high frequency of the train are also more obvious and there is still no relevant theory and calculation method.In view of this,the research of dynamic load characteristics and design method for heavy haul railway tunnel structure is of great significance.In this dissertation,a variety of research methods including large-scale in-situ excitation test,long-term remote monitoring,theoretical derivation,numerical simulation and data research are applied.Based on two heavy-haul railway,Zhangtang railway and the Wari railway,the dynamic load characteristics,analytical solution of load,calculation model of structure and the prediction method of fatigue damage have been studied.The main research results are:The dynamic characteristics of single and double track heavy-haul railway tunnel structure under conditions of axial weight varying from 27 t to 30 t,surrounding rock quality varying from class III to V were clarified by field measurement.It is concluded that the dynamic response of the tunnel base structure is much stronger than that of the arch wall structure,and the dynamic response within the range of the track is the most intense.The obtained dynamic load distribution characteristics and vertical load transmission rules of layers in the base providec the research basis for the analytical solution of the load.With a combination of the measured data and existing codes,a theoretical calculation method of dynamic load on ballast bed was put forward with according to the type of wheelrail interaction and the stress characteristics of ballast bed of heavy-haul railway tunnel.The analytical solutions for the surface loading of the filling of the ballasted tunnel and the unballasted tunnel were obtained with stress diffusion angle theory respectively,which provides the basis for the calculation of the stratum structure model,the solid element spring model and the fatigue damage analysis.Using the elastic layer system,the Busschnee solution for the dynamic loading of the tunnel invert surface is deduced,which provides the initial load conditions for the beam model and the load structure model of the elastic foundation.Overlying the structure internal force computation of the load and unload sections with the Winkler foundation beam calculation theory,model I was established and with which the internal force of the tunnel invert/base structure can be calculated independently;by setting up the contact elements between the structural layers of the stratum structure model,the model II was built on the basis of the tunnel filling surface load,which can be used to calculate the interlayer distribution and transfer of the dynamic load in the base structure.An equivalent simulation of surrounding rock's restraint with spring element makes model III available to simulate surrounding rocks detailly.Model IV,in which the self-weight loading of the base structure and the equivalent load of trains were applied on the surface of the tunnel invert / base structure,can be used for simplified calculation.When compared with the field testing results of internal forces,all the computation of these four calculation models are greater,which means that results of these four models can be used in the design of heavy-haul railway tunnels.The three kinds of side ditch of the heavy-haul railway tunnel obtained from statistical analysis are simplified into two stress types,separate stress and integral stress.With analytic solution of the structural internal force based on the plane strain elasticity mechanics,the force characteristics of the lateral groove can be analyzed.With the numerical calculation,the fatigue damage distribution characteristics and evolution law of the tunnel base structure are obtained.It is concluded that the fatigue damage is mainly concentrated near the position of the heavy-haul tunnel track which is determined by the dynamic load effect,and the fatigue life increases gradually from top to bottom.A comparison for the influence on the fatigue life of tunnel structure between the axle load and surrounding rock level shows that the axle load is the main factor.Finally,fitting formulas for fatigue life prediction of different parts in the tunnel base structure were obtained.