دانلود رایگان مقاله انگلیسی پاسخ دینامیکی بستر خاکی زیر ریل های دوتایی راه آهن سریع السیر - الزویر 2018

ABSTRACT

The majority of high-speed railways around the world is in China and more than 90% of the high-speed railways in China are double-line. At present, studies on the dynamic responses of subgrade under double-line high-speed railways are quite limited due to the complexity of these railways. In this study, a three-dimensional finite element model was developed using ABAQUS software for a double-line ballastless track-subgrade system subject to 8-carriage moving constant loads. The dynamic responses (specifically the vertical stress, displacement, velocity and acceleration) were determined at three points on the subgrade surface (Point A, Point B, and Point C) for trains travelling at different speeds (250, 300, and 360 km/h) and line patterns (unidirectional and bidirectional operations). The vertical stress distributions at selected points on the subgrade surface at these train speeds and line patterns are presented, and the vertical stress distributions along the soil depth of the subgrade at Point A and Point B are discussed. The key findings of this study are as follows. The maximum vertical displacement at the three observation points decreases as the train speed increases whereas the absolute maximum vertical velocity slightly increases as the train speed increases. In bidirectional operation, the maximum vertical stresses occur under the rails on the subgrade surface and the stress distributions are asymmetric. At Point A (point on the subgrade surface underneath the left rail in the left line), the vertical stress decreases along the soil depth and the vertical stress attenuation is more pronounced for bidirectional operation. However, at Point B (point at the centre of the subgrade surface), the vertical stress increases along the soil depth. The vertical stresses at Point A and Point B tend to be close to one another with an increase in soil depth such that the values are nearly coincident in the embankment layer within the range of train speeds investigated in this study.

4. Conclusions

A 3D FE model was developed in this study in order to examine the effects of train speed (250, 300, and 360 km/h) and line patterns (unidirectional and bidirectional operations) on the dynamic responses of subgrade subject to high-speed moving constant loads. The following conclusions are drawn based on the findings:

(1) The maximum vertical stress increases with an increase in train speed for both unidirectional and bidirectional operations. The maximum vertical stress of the subgrade increases by 6% and 2% for bidirectional and unidirectional operation, respectively, as the train speed increases from 250 to 360 km/h. However, the maximum vertical stresses are generally lower for bidirectional operation.

(2) The vertical displacements are higher at all observation points (Point A, Point B, and Point C) for bidirectional operation, indicating that the subgrade structure sustains more external force.

(3) The vertical velocity slightly increases as the train speed increases from 250 to 360 km/h. The vertical velocity-time history curves are mainly controlled by the bogie loads, rather than the wheel loads. The absolute maximum vertical velocities of the subgrade are 10.64 and 9.50 mm/s for bidirectional and unidirectional operation, respectively, at 360 km/h.

(4) The maximum vertical acceleration at Point B is 0.54 m/s2 for bidirectional operation, which is twice the value for unidirectional operation.

(5) The vibrations at Point B are more severe for bidirectional operation compared with those for unidirectional operation.

(6) At the subgrade surface, the vertical stresses are maximum under the rails and the stress distributions are asymmetric for bidirectional operation.

(7) The vertical stress attenuates along the soil depth at Point A and the vertical stress attenuation is more pronounced under bidirectional operation. However, a different trend is observed at Point B, where the vertical stress amplifies along the soil depth. The vertical stresses at Point A and Point B tend to be close to one another with an increase in soil depth such that the values are nearly coincident in the embankment layer within the range of train speeds investigated in this study.