Study On Static And Dynamic Mechanical Properties Of Railway Over Cross Tunnels And It’s Application

This dissertation focused on deeply buried over-cross railway tunnels, via the comprehensive approaches of theoretical analysis, numerical simulation and engineering practice, did a systematic study on the existed tunnel lining’s deformation, the rule of surrounding rock pressure variation, the tunnel structure internal force alteration and dynamic response with train load, and combined with the actual project, Wumengshan tunnel&Xinmeihuashan tunnel over-cross tunnels project, carried out a comparation research on different forms of over-crossing structures. This dissertation obtained the following achievements:1) Using the method of three-dimensional numerical simulation, summarizing from a large number of conditions calculation results, this dissertation deduced the track bed deformation prediction formula, which included the variables of the minimum spacing, the surrounding rock conditions and the building consequence of the two tunnels, and gave out the suggested interval allowable values to avoid any impacts on the security of the existing tunnel’s high-speed railway operation.2) Whether the new tunnel building beneath or on-acrossing the existing tunnel, the surrounding rock pressure of the existing tunnel would decrease in varying degrees. At the three positions of arch foot, side wall and spandrel, this phenomenon was much more obvious. This dissertation made a determination on the existing tunnel’s influenced scope under different spacing and rock classifications. When the surrounding rock conditions were good enough, for the existing tunnel, the influence scope of on-acrossing style was smaller than the building beneath one. Took the rock pressure variation amplitude as the evaluation criteria, we provided critical value of uninfluenced clearance for over-crossing tunnels project, which will bring forward reference to the similar projects.3) For the deep double track tunnels with elliptical section, building a new tunnel closely would lower the whole ring’s axial force of the old tunnel’s lining structure. Along with the increase of the clearance between two tunnels, structure axial force downward trend slowed down; Along with the surrounding rock conditions turning worse, the structure bending moment and axial force under the same clearance decreasing linearly. In the condition of the new tunnel building undercrossing, full ring of axial force dropped, while bending moment rose, stress state significantly turning worse. In the case of new tunnel building over across, with the axial force dropped, in different ways, bending moment also generally decline, and the positions where transverse or longitudinal structure safety factor decreased would be less than the building under cross style, So to the building over pass form exert less impact to internal force of existing tunnel lining than the building under pass style. So that the similar project should firstly consider the former construction style.4) This dissertation corrected the commonly used one-dimensional sine vibration force model for train dynamic loads, so that solved the problem that it would generates upward tension to the rail when using the original model to simulate high-speed train load, now made it much more suitable for v≥300km/h high speed railway research, and this dissertation also put the model forward into three dimensional simulation.5) Compared with conventional section, all the displacement, velocity and acceleration in overpass section were significantly amplified. At the cross point, this dissertation set three different structures, they were separated building, half-separated building and building in union, via the comparison study on displacement response, vibration damping and transverse longitudinal internal force analysis of each style of the three, and the results showed that the framework-connecting walls structure form, which connecting the two tunnels together, was the best choice.6) For the case of two tunnels were under construction simultaneously, each one had the trend of producing deformation towards the other. Research revealed that the surrounding rock final displacement disturbance of the first tunnel would be less than the later built one. The lower the disturbance to surrounding rock, the smaller construction risk would be and the more safety structure was. Therefore, we could determine each tunnel’s construction progress according to different important degrees of the two tunnels and the actual construction conditions. It means that the more important one should be build first.7) In this dissertation, through detailed dynamic simulation calculation, this dissertation proved that, the design scheme and construction process plan of the framework-connecting walls form for over cross section was reasonable and feasible, and this construction scheme has been carried out successfully in the WuMengShan tunnel&Xinmeihuashan tunnel over cross tunnels project, and that were worth reference for similar project.