Investigation of Ballast Degradation on Bike- Dewele Railway Line
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Date
2023-10
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Addis Ababa University
Abstract
Rail tracks are often placed on ballast which offers the desirable resiliency to cyclic loads. Modernization of railway transportation in terms of increasing axle load and speed focused on ballast layer as a key component of conventional railway track. The ballast layer undergoes gradual and continuing degradation with usage and time due to increasing traffic passage, loads and speed. The rate and magnitude of ballast degradation depends on ballast quality, environmental exposure, geometry profile, speed, and number and magnitude of axle loadings. Intolerable degradation cause track geometry deterioration due to track settlement as a result of excessive permanent deformation of the ballast layer. Understanding the degree of ballast bed degradation under cyclic loadings helps to either making standardization or planning for maintenance schedule.
This study was conducted to determine the extent of ballast degradation along the Bike-Dewele section of the Ethio-Djibouti railway line following five years of operation. This study collects data on ballast degradation through visual inspections in the field and laboratory tests. Visual inspections were conducted following such as vegetation growth, surface fines, crib and shoulder ballast missing, cobles on the main track, more degraded ballast sections. On samples of ballast collected from ten (10) locations along the Bike-Dewele sections, laboratory tests including gradation (sieve analysis), Los Angeles Abrasion, shape tests (Elongation and Flakiness) and Fouling index were conducted, as well as design and as-built data reviewed. Gradation was determined by calculating the percentage shift of each PSD curve from the as-built PSD curve limits. Additionally, other tests were compared to the recommended standard at each location.
The investigation discovered that the ballast on the Bike-Dewele section within five years of operation, there is significant deterioration of ballast, as shown by the PSD curves shifting above the as-built maximum values of 40-115 percent. Improper ballast aggregate addition has been found, as indicated by PSD curves dropping below the as-built minimum value of 41-180 percent. The majorities of ballast aggregates throughout the Bike-Dewele stretch are broadly graded and fall within as-built data, while others are even more broadly graded than as-built data. The resistance of the present ballast to abrasion is between 76 and 87%, when the values are compared to the recommendations in various standards, it can be concluded that the ballast is still capable of carrying the imposed loads. The shape property index tests show that particle shape has been rapidly changing (highest FI value is 37% and highest EI value is 46%) and the material is deteriorating. While conducting a field investigation, discovered that several portions of the ballast were highly fouled, but that sampling was not permitted.
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Keywords
Ballast; Degradation; Investigation; Laboratory tests; Field Inspections