Research On Dynamic Response Characteristics And Evaluation System Of Heavy Haul Railway Tunnel Base Structure

The problem of heavy haul railway tunnel disease is extremely prominent, has seriously affected the traffic safety of railway lines. Understanding about stress state and dynamic response of heavy haul railway tunnel base structure under large train axle load is lacked, and evaluation method for service status of common railway tunnel can not apply to heavy haul railway tunnel. Thus, clear of stress characteristics and dynamic response of railway tunnel base structure under large axle load, establishment of heavy haul railway tunnel base structure service state evaluation system, and reasonable assessment of heavy haul railway base structure operating state, is of great significance to the construction and operation and maintenance of heavy haul railway tunnelFirstly, type and status of heavy haul railway tunnel base disease are analyzed by on-site survey. Secondly, horizontal distribution law and vertical transfer law of heavy haul railway tunnel base structure dynamic stress under train load are studied by field testing, and internal relationship between dynamic stress and vibration acceleration of heavy haul railway tunnel base structure and factors such as axle load and train speed is analyzed. Thirdly, elastoplastic damage constitutive model of concrete is constructed based on the basic principles of thermodynamics, then this model is implemented and verified in FLAC3D. Fourthly, this model is used in numerical simulation which is carried out for dynamic response and fatigue damage of heavy haul railway tunnel base structure under train load, regression analysis is used to get the load transfer rate of invert under different design parameters of tunnel base structure. Finally, service state evaluation method of heavy haul tunnel base structure is established based on fuzzy mathematical method, the implementation process of this method is described combined with engineering example. The main research contents and conclusions are presented as follows:(1) Test datas of Shuo-Huang railway tunnel disease are analyzed systematically. Test results show that:1) The disease incidence of heavy vehicle line is higher than tunnel centre and empty vehicle line.2) The most common disease of tunnel base structure is concrete damage, followed by uncompacted surrounding rock beneath base structure, foundation subsidence also occurs.3) The higher the rock classification is, the more serious the situation of insufficient concrete thickness and uncompacted surrounding rock is.(2) Dynamic response and vibration characteristics of heavy haul railway tunnel base structure are mastered. There include:1) Horizontal distribution of dynamic stress along base structure. Horizontal distribution law of vertical and horizontal dynamic stress appears as "greatest at heavy vehicle line, medium at tunnel centre, and smallest at empty vehicle line".2) Vertical distribution of dynamic stress along base structure. Vertical dynamic stress attenuates significantly along the vertical direction, vertical dynamic stress is less than 20kPa when 30t axle load transmits to the bottom of invert, far less than the initial stress of invert before the action of train load. Horizontal dynamic stress shifts from compressive to tensile along the vertical direction.3) Dynamic stress is roughly linear with axle load, and slightly affected by train speed.4) Vibration acceleration is linearly proportional to train speed, track structure and axle load have little effect on vibration acceleration.(3) Elastoplastic damage constitutive model of concrete is constructed based on the basic principles of thermodynamics. Difference scheme of this constitutive model is derived, this model is implemented in FLAC3D by C++program, validity of this model and correctness of model program are verified by simulating laboratory tests.(4) Numerical simulation which uses concrete elastoplastic damage constitutive model is carried out for dynamic stress response of heavy haul railway tunnel base structure under train load. There include:1) Regression analysis is used to get the load transfer rate of invert under different design parameters of tunnel base structure, empirical correlation between vertical dynamic stress of invert, rock classification, invert thickness and invert span ratio.2) If the actual construction status of tunnel is coincident with the ideal status of tunnel design, tunnel base structure can meet the operational requirements, and no damage occurs. When soften of surrounding rock or void beneath base structure or breakage of base structure reaches a certain level, damage will appear in tunnel base structure.(5) Service state evaluation method of heavy haul tunnel base structure is established. Follow the principles of scientific, completeness, and so on, service state evaluation system of heavy haul railway tunnel base structure is divided into two-levels fuzzy comprehensive evaluation model which includes target layer, rule layer and index layer. The index classification criteria is determined in accordance with relevant norms, on-site inspection and monitoring data, and numerical calculation results. Weight of factors in index layer is determined by extension AHP method, Weight of factors in rule layer is determined by improved gray correlation method, and service state level of heavy haul railway tunnel base structure is determined by fuzzy vector single-valued method. The implementation process of this method is described combined with engineering example.