Exploration Of Design Technique On Substructure For 400km/h High-speed Railway And 40t Axle-load Heavy Haul Railway

The high-speed passenger traffic and heavy-haul freight traffic is the strategic planning of railway development in China.As the most important infrastructure under the line,the subgrade is required to have good qualities,such as strength and long-term stability,to ensure the safety and comfort of transport.However,the continuous improvement of train speed and axle load exacerbates interactions in vehicle-track-subgrade system.For the high-speed railway,the quantitive use of ballastlees track has weaken the suitability of deformation from substructure and thus subgrade disease has emerged gradually with the affection of the high-speed load,geoloey environment and weather conditions,which becomes a urgent problem needed to be solve after the quick development of the construction of high-speed railway.For the heavy haul railway,the improvement of axle load leads to the increase of dynanmic load,the decrease of the wheel bases of front and rear cars aggravates the superposition effect,the long marshalling increases the action number of wheel load.Therefore,the dynamic failure and railway deformation is intensified and the settlement rate of subgrade changed quickly and then the maintenance workload is increasing.In order to make substructure in good working conditions,subgrade in China adopt layered-structure system,which is enhanced by graded broken stone,but still have lots of problems,like the differentiation of high-speed railway and heavy haul railway is not obivious,the subgrade structure form is simple and the requirements for thickness of layer and filling have an empirical tendency.Since the design and construction standard of subgrade affects the quality of railway and the safety and effectiveness of transport,it has definite engineering background for researchers to explore an integrated and whole-life cycle design method for subgrade.The improvement of design method for subgrade has practical guiding importance to promote the development of high-speed and heavy-haul railway in China.In this paper,based on the differentiation of technical features of high-speed railway and heavy-haul railway,methods like theoretical analysis and numerical calculation are adopted.The characteristics of substructure under train loading are analysed.The subgrade dynamic response by considering the track irregularity conditions is analysed.Combining with the experimental analysis of the cumulative deformation state of existing typical subgrade filler under the action of cyclic loading and using the design method which involves three critiria,that is,the dynamic strength,bearing stiffness and long-term stability as the key,research work on the design technique for high-speed railway and heavy haul railway is conducted.At last,the design parameters that are suitable for subgrade structure of ballastless track for 400km/h high-speed railway and ballasted track for 40t axle-load heavy haul railway are proposed.The work of this paper is listed as follows.1)Analysis on characteristics of substructure under train loading.One loading-unloading process of the dynamic stress in ballastless track subgrade is completed by two-axle load of the same bogie under China Rail High Speed(CRH)load.An affected area of train loads which is distributed approximatly as a rectange would be formed after the process of transmission and dispersion by track under the action of two-axle load.Then,the load model can be simplified to be trapezoidal distribution along the longitudinal direction and uniform distribution along the lateral direction.Based on the technical characteristic that the wheel bases of front and rear cars are close to the rigid wheel base about several export-oriented 40t axle-load ore gondola cars,the proposed four-axis load mode,4Z1800/2400,could accurately reflect the superposition effect under train loads.Through the summary of the research results of dynamic influence coefficient,the dynamic influence coefficient is divided into two categories according to the train load,that is,the dynamic coefficient of ultimate load,which can reflect the dynamic impact of train load under ultimate condition,and the constant load dynamic coefficient,which can reflect the cumulative deformation effect of long term cyclic loading.2)Analysis on subgrade dynamic response by considering the track irregularity conditions.According to the structural characteristics of CRTS ? slab ballastless track and ballasted track,the vehicle-slab track coupled dynamic model and vehicle-track coupled dynamic model are set up respectively based on the vehicle-track coupled dynamics.Then afterwords,the response of subgrade for CRTS? slab ballastless track considering the PSD of ballastless track irregularity and the ballasted track considering the PSD of ballastless track irregularity are computed.The research shows that under these two track irregularity,the dynamic coefficients along the line are all distributed normally.3)Research on the design and calculation method for subgrade of ballastless track of 400km/h High-speed Railway.According to the design characteristics of ballastless track substructure,an calculation method for cyclic shear strain is established by considering the mechanical properties of soil and plastic index.Based on the distribution of train load for ballastless track and the response of subgrade under PSD,the design method of the subgrade structure for 400km/h high-speed railway is proposed.At last,the design parameters that suitable for the subgrade structure of ballastless track for 400km/h high-speed railway are put forward according to different types of filling which are allowed to be used by the code.4)Research on the design technology for subgrade of 40t axle-load heavy haul railwayThe method for thickness calculation of subgrade is established with the principle which avoids cumulative deformation for embankment.Regard the cumulative deformation is in the slowly stabilized state as control target,the technical standard proposal which suitable for the subgrade structure of 40t axle-load heavy haul railway is put forward,that is,the thickness of subgrade bed is 3.5m which requires K30?110MPa/m for the filler of embankment,and the thickness of surface layer of subgrade with graded broken stone is 0.7m which requires K30?130MPa/m for the filler of bottom layer of subgrade.