Keywords: increased axle loading, railway foundation materials, railway cyclic loading, cyclic triaxial testing.

The transportation of bulk and heavy freight by rail is beneficial from an economic, environmental and safety perspective, such that in South Africa, there are strategic plans to increase some of the corridors from 20 to 26 tonnes per axle. This has therefore created a need to understand the engineering behaviour and performance of each railway track component at higher axle loading in order to maintain a sustainable railway network. The purpose of this work is to analyse the behaviour and performance of railway formation materials, particularly the subballast and subgrade layer at an initial axle loading of 20 tonnes per axle, increased to 26 tonnes per axle. The methodology involved the characterisation of railway loading, experimental work using an advanced cyclic triaxial apparatus on materials representative of the subballast and subgrade material, followed by detailed processing, analysis and interpretation of the results and conclusion. Based on the test results, the behaviour of both materials when loaded at cyclic stresses equivalent to 20 tonnes per axle was in dilation and the plastic strains remained stable. At cyclic stresses equivalent to 26 tonnes per axle, both materials underwent a phase-transfer in soil behaviour from dilation to contraction and upon the phase-transfer the plastic strains became exponential. It is therefore concluded that for design and maintenance of railway foundations, geomaterials that tend to undergo a phase-transfer in soil behaviour from dilation to contraction should ideally not be used for operation in railway track foundations, as they might result in excessive plastic deformation and differential settlement.

download the full-text of this paper (PDF, 1223 Kb)

go to the previous paper
go to the next paper
return to the table of contents
return to the volume description