Study On The Structure Optimization Of Double-Block Ballastless Track On Subgrade In Area Of Large Temperature Variation

With the rapid development of high-speed railways in China, the construction of unballasted track received substantial and extensive application. Double-block ballastless track is a main structure of unballasted track system in China, because of its advantages of simple structure, good integrality, convenient construction, low construction cost, etc. But excessive tensile stress which appeared in services period of double-block ballastless track could cause many diseases in track concrete layer such as cracking, crushing and up-warping, etc. The operation and analysis experience show that the main reason is the complex temperature stress in track concrete layer.Lanzhou-Xinjiang double railway lines used double-block ballastless track and the temperature difference between these two areas is relatively large, so it is necessary to optimize the design of double-block ballastless track in this area. This is of the important theoretical significance and practical value for the design theory and application of double-block ballastless track.This paper is based on the background of the double-block ballastless track in Lanzhou-Xinjiang double railway lines. Through the theoretical analysis and field test, the adaptive temperature range of the double-block ballastless track was determined. The paper puts forward a structure design method of the double block ballastless track which was suitable for the temperature of Lanzhou-Xinjiang double railway lines. This paper’s main work is as follows.1. The temperature characteristics of double-block ballastless track in Xinjiang was studied.The temperature characteristics of double-block ballastless track in Lanzhou-Xinjiang double railway lines based on field test and research on the historical meteorological data. The historical meteorological data research shows that the maximum temperature is 47.7℃ in Turpan, and the lowest temperature is -41.5℃ in Urumqi. And the maximum annual temperature difference is 83.6℃ in Urumqi. The field test in a year shows that the maximum temperature of track concrete layer is higher than the highest temperature 5℃, and the minimum temperature is equal to the minimum temperature value.2. The mechanical model of double-block ballastless track was established.The mechanical model was established based on double block ballastless track structure and load condition, meanwhile the influencing factors of temperature, temperature gradient, structure layer relations, train loading roadbed, etc was considered.3. The adaptive temperature range of continuous double-block ballastless track on subgrade was studied.In this paper, the temperature load was considered which leads to track concrete layer cracking, arching, crashing. From this, it was found that the slab maximum allowable temperature rose and dropped. The calculation result shows that the track concrete layer will not lose stability before the concrete is crashed. Without considering the temperature gradient conditions, the maximum temperature drop which the track concrete layer can withstand is 30℃, while the maximum temperature rise is 65℃. The effects of temperature gradient should be converted according to the corresponding formula. In Lanzhou-Xinjiang double railway lines, under the effect of the maximum temperature gradient, double-block ballastless track can be adapted to the temperature range of 60 ℃, so continuous double-block ballastless track on subgrade cannot be directly applied in this area.4. The feasibility of continuous track concrete layer with false joint structure design was studied.The scheme of track concrete layer with false joint can release the temperature force and improve the adaptive temperature range of the double-block ballastless track. By calculation, the reasonable joint depth is 1/4h-1/3h and interval distance is 4-6m. This scheme can make the double-block ballastless track temperature adaptation range raise by 19℃. Without considering the temperature gradient conditions, track concrete layer with false joint can be adapted to the temperature range of 115℃.In Lanzhou-Xinjiang double railway lines, under the effect of the maximum temperature gradient, it can be adapted to the temperature range of 79℃. The field test shows that, the damage appeared at false joints and other parts has few damage.There is a gap between the temperature difference in the test section and the historical limit temperature difference, so there is less diseases. With consideration of the theoretical analysis, the scheme of track concrete layer with false joint is not available in the Lanzhou-Xinjiang double railway lines.5. The design method of the unit slab of the double block ballastless track on subgrade was proposed.Based on the design of unit slab track, this paper puts forward the design scheme of unit track concrete layer. The reasonable design length of the unit slab was obtained by mechanical coupling model, whose length cannot exceed 8.2m. To increase the integrity of the slab, the scheme of large unit track bed with false joint was put forward. The field test shows that unit slab schemes had environmental adaptability.Through applying the theoretical method to the analysis of continuous double-block ballastless track on subgrade in area of large temperature variation, a design scheme is put forward. It guides the optimized design of the structure in the Lanzhou-Xinjiang double railway lines and it offers the theoretical reference to the other projects.