Research On Effect Of New-built High-speed Railway On Adjacent Operating Railway Subgrade In Service Status

With the rapid development of high speed railway, the parallel phenomenon of new built and existing railway becomes more and more problematic. The construction of new built railway often affects the safety of adjacent existing railway subgrade, which often leads to overly large deformation. Thus, analysis only considering the stability of subgrade is not enough to ensure the safe operation of the existing railway. Therefore, the research on new built high-speed railway's effect on the subgrade service status of adjacent operating railway is carried out in this dissertation. Relying on the Shanghai-Nanjing intercity railway projects, through the static and dynamic field test, theoretical analysis, finite element calculation and data analysis methods (such as track inspection car), located in a test section adjacent to the new and old line position, test items such as deformation stress and dynamic response of operating subgrade are tested. During different construction stages, subgrade deformation and its internal stress are calculated by various mechanics formula. Numerical analysis is adopted to obtain subgrade service and limit state under the construction disturbance. Thus, some engineering measures are suggested and implemented, on the basis of the test and calculation results, and an assessment system of operating subgrade condition is established. Some major achievements of this research are as follows:(1) In view of the new built high-speed railway construction effecting adjacent existing railway subgrade, a set of methods of static and dynamic test are set up to monitor the embankment safety. Subgrade slope toe of existing railway subgrade is tested in static testing, whose results show that the most sensitive index is horizontal displacement; Dynamic test is carried out to obtain subgrade vibration acceleration, vibration displacement change distribution, as well as impact of vehicle types and speed, which realize the dynamic monitoring for existing railway subgrade under construction disturbance.(2) Due to the deformation and stress of existing railway subgrade in different areas cannot be monitored under construction disturbance, based on the cylindrical cavity expansion theory, considering the subgrade and foundation pit excavation and foundation, established analytic formula is given to calculate radial stress and displacement of adjacent existing subgrade. Hence, calculation method considering effect of clump of piles is proposed, whose results are verified by test data. Thus, inside deformation of existing railway subgrade can be predicted, which could provide theoretical support for similar adjacent construction.(3) Finite element analysis is used to analyze the three phases of construction (including pit excavation, piling, subgrade filling), which concluded that the most dangerous stage is during excavation, and the influence of train speed is analyzed; On this basis, long-term stability of operating railway is obtained under foundation pit flooding. Dynamic disturbance influence of pile driving vibration on adjacent existing subgrade is also obtained; In addition, through the numerical analysis, the existing subgrade vibration displacement, vibration acceleration, and lateral displacement threshold are acquired, which provides safety control standard for test and calculated data. Thus, monitoring and early alarm for existing railway subgrade are optimized.(4) Considering the instability and overrun deformation of existing subgrade, foundation treatment design optimization and slope protection measures are put forward and implemented successfully in engineering field. Original design of CFG pile is recommended to convert into solid gravel pile and pipe pile. The construction technology of static pre-stressed pipe pile adjacent to existing railway is proposed, which has been verified as ministerial declaration method. The above engineering measures effectively ensure the safety for operating the existing railway.(5) Aiming at problems such as assessment factors of operating railway subgrade condition are complex, no authority or studies established any subgrade condition assessment system, based on grey theory and neural network principle, existing subgrade condition assessment model is established, whose evaluation index features as subgrade deformation stress (by field test), TQI (by track inspection car analysis), stability (by theoretical calculation). The grey clustering method is adopted for index normalized processing, and BP neural network is used for reducing error of the weight distribution process, which can realize the operating state of subgrade assessment under the influence of multi factors eventually.