Road and Transportation Engineering

Permanent URI for this collection

http://etd.aau.edu.et/handle/12345678/137

Browse

Browsing Road and Transportation Engineering by Author "Abesha, Berhanu (PhD)"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Standardization of Guidelines for Railway Track Infrastructure Subsystem for Railway System of Ethiopia
    (Addis Ababa University, 2012-01) Gebeyehu, Yeserah; Abesha, Berhanu (PhD)
    Railway transportation, which is needed in the achievement of effective development, is an efficient, cost-effective and it is environmental friendly transport system. In addition to the low railway network connectivity in Ethiopia like other developing countries, the available one is not modern; has low capacity and is insufficient to facilitate transit trade; and also Ethiopian railway transport has not standardized guidelines to design the system. In this study an attempt was made to standardize guidelines for railway track infrastructures specifically track geometric parameters and track structural elements for conventional lines in Ethiopia. To achieve such objectives the research had a methodology of a task involving literature review; discussion and comparison of different country standardization practice; and different data collection that contribute for standardization of guidelines for railway system in Ethiopia. Standardization of guidelines for different track infrastructure subsystems for Ethiopia context was done based on topography, climatic condition and availability of track construction material, and different literature reviews. Track cant of a normal limiting value of 160 mm was recommended to reduce or eliminate lateral acceleration created due to small curve in difficult topography of Ethiopia. In addition a cant excess of as small as 70 mm was recommended in avoiding damage of low rail by heavy freight train; and correspondingly this can be achieved by increasing the value of cant deficiency for fast train. A gradient of up to 3.5% and/or greater value was recommended for lines constrained by topography. Even if the selection of steel rail grade is based on avoiding rail wear and rolling contact fatigue; standard steel rail strength i.e. R260 is recommended for all lines including for the whole range of curvatures due to high investment cost of higher quality steel grade that are recommended for sharp curves (curves are suffering from high rail wear). On the other hand, the recommended method of selecting fastening systems is a matter of satisfying safety of the lines. The specification of ballast and subballast depend on the availability of track construction material; and the track construction material availability in Ethiopia is, more or less, not a problem in construction industry even in the eastern part of Ethiopia where inadequacy of construction material are expected. An attempt was made to find a suitable range of ballast ii gradation which fulfills the objective of good strength (well graded) without significant reduction in permeability of ballast (uniform graded) using a coefficient of uniformity between 2.2 and 2.6, moderately graded ballast was recommended. In addition the specification of subballast material was determined based on filter principle of drainage criteria using subgrade material size distribution. The problematic subgrade soil, placed under subballast, should be replaced or improved to achieve the required strength characteristics of subgrade layers. The appropriate type of tests was selected to define the characteristics of each track substructure layers (ballast, subballast and subgrade soil). Key Words: Track, Cant, Cant Deficiency, Cant Excess, Rail, Fastener, Sleeper, Ballast, Subballast, Subgrade and Safety