In the design of rail track structures where the subgrade cannot achieve the desired
capacity, enabling the required standard of track geometry to be maintained for the speed,
axle load and tonnage to be hauled, a capping layer of granular material is placed
between the natural ground or the embankment fill material and the ballast to protect the
underlying weaker layers.
In spite of the important role played by the capping layer, very little research has been
carried out on its performance. The current practice of design of the capping layer,
therefore, is based on working stress philosophy where reduced levels of stresses are
assumed not to degrade the subgrade. Even on tracks containing a thick ballast layer that
ensures allowable levels of working stress the subgrade has been found to have
permanently deformed. Design of capping layers based on plastic deformation,
therefore, appears appropriate. This thesis aims at determining the load levels that cause
detrimental plastic deformation in the capping layer.
The suite of material properties that characterise plastic deformations of capping layer is
neither readily available nor easily determined. This thesis proposes a cheaper method of
evaluating a range of capping layer material properties using penetration tests on
specimens contained in California Bearing Ratio (CBR) test moulds coupled with a finite
element modelling based back calculation technique. The suite of material properties
thus determined are used for the simulation of the behaviour of capping layers under the
boundary and loading conditions similar to those in practice. The predicted results are
validated using laboratory experiments on large size capping layer specimens.
| Identifer | oai:union.ndltd.org:ADTP/217333 |
| Date | January 2006 |
| Creators | RADAMPOLA, Senanie Sujeewa, senanie.s.radampola@mainroads.qld.gov.au |
| Publisher | Central Queensland University. Centre for Railway Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.library.cqu.edu.au/cqulibrary/disclaimer.htm), Copyright Senanie Sujeewa RADAMPOLA |
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