Effect of Ballast Bonding and Stabilized Soil Modulus on Railway Track Transition zone Settlement
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Date
2016-12
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Addis Ababa University
Abstract
Railroad substructure deforms and degrades progressively under heavy cyclic loading. The track subsoil and ballast have the most significant contribution for the substructure deterioration. Track degradation and settlement occurs throughout the track but particularly sensitive are transition areas between ballast track and ballast less track, switch and crossing areas, turn out areas and rail joints due to dynamic impacts that come from the abrupt change in track stiffness. Track stiffness has a profound significant in design and construction stages of the railway track. Safe travel and life time performance of a track depend on the unvarying track stiffness.
In spite of that, varying the track stiffness is bound to happen, particularly in the transition zone, where the rigid track connects to a conventional ballasted track. In this critical point track stiffness varies suddenly and it causes differential settlement, which is the major source for deterioration of tracks and sub structures at transition zones. Different solutions have been applied on the super structure of the track to make gradual stiffness transition, such as the use of gradual pad stiffness long sleepers and auxiliary rail.
This critical railway infrastructure problem demand repeated track preservation work, especially frequent ballast bed maintenance. In order to increase the performance of railway track, to avoid frequent maintenance works and to reduce costs the better solution is track substructure reinforcement. Reinforcement of the track by bonding ballast using polyurethane geocomposite and stabilizing the subsoil is a candidate solution to these problems. This paper focuses on the applicability and potential benefits of ballast bonding technology and soil stabilization to railroad bridge approach transition zones. The prominence of this study is conducted on the investigation of the characteristics of track substructure at transition zone under the train moving loads by improving ballast and subsoil strength. For that reason, well-known commercial finite-element method package ABACUS- CAE has been used to investigate the dynamic behavior of the transition zone under the passage of trains. The results of the dynamic analysis are presented and compared in two set of conditions; one the non-improved or low strength substructure without gradual stiffness change and the other by considering the improvement in the substructure by intensifying the substructure performance through constructing two-part transition section. These are improved and non-improved parts. The geometry of improved parts of the ballast and subsoil changes gradually to mitigate stiffness variation. Finally conclusion and recommendation are presented based on the finite element results. From the finite element result the vertical displacement of the ballast and the sub grade has been lowered to the acceptable range due to the improved modulus of elasticity of the substructure. The vertical acceleration on the rail is also absorbed to zero when the substructure is improved.
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Keywords
Track transition zone, Track stiffness, Ballast bonding, Soil stabilization