Övergångszoner mellan ballastspår och ballastfria spår
Abstract: In today’s railway facilities there are several types of track systems with different characteristics, which must interconnect in order to obtain a closed network. The area where a track system passes over into another track system is called a transition zone. The track systems’ different characteristics chiefly consist of differences in settlement tendency and track stiffness. The transition zone is described as the weakest link in the railway track by Nyquist (2010). The thesis is a review of the knowledge concerning the construction of transition zones, as well as what impact the construction generates in regard to its design and maintenance. The knowledge review of the transition zones include studies based on interviews, documents, previously conducted measurements, as well as site visits to the reference projects: Citytunneln in Malmo¨, Nya A°rstabron in Stockholm, the Metro in Copenhagen and Drogdentunneln in O¨resundsfo¨rbindelsen. A purpose-built transition construction from Austria, V-TRAS, has been studied, based on an interview and document in the form of a concept description. Also a theoretical review and interview has been performed with a Doctor of Technology, who has conducted research of transition zones. The result shows that Citytunneln has relatively well-designed transition zones, working as designed. There are settlement tendencies in the transition zones, as a consequence improvements have been proposed for preventing further deterioration of the existing condition. With today’s design, the transition zones on Nya A°rstabron show greater settlements and maintenance need, in comparison to the other reference projects. Regarding the transition zones in the Metro, two of the ten transition zones lack a construction for stiffness equalisation. The transition zones without the construction demonstrates significantly greater maintenance need in comparison to the other transition zones, which work well. Among all transition zones in the reference projects, the transition constructions in Drogdentunneln differentiate as the better, after a reconstruction was made. As of today, they are well adapted to the surrounding conditions, exemplified by the low maintenance need. The V-TRAS module is applied in both new and existing tracks, and can be adapted to existing conditions as well. It seems to work well, but it should be noted that the period of use is only two years. Finally, theoretical experiences of transition zones are presented. The gradual or abrupt designs of the change in track stiffness in the included reference projects are not to be recommended. Instead it is recommended to use the error function, with an S- shape, to obtain a smooth transition in track stiffness. In summary there are generally large differences between transition zones, in particular between transition zones with, respectively without an adapted design. It is found that a construction of the stiffness transition is important, especially as a preventive measure against settlements.
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