In South Australia, high strength polymer geogrids, together with non-woven geotextiles have been used to reinforce railway ballast. A case study is presented from a project across soft soil conditions and v.ery high ground water table. In this case the adopted solution involved encapsulating the railway sub-ballast in high strength bi-axial oriented polymer geogrid, to form a stiff ‘raft’. The method involved excavating to sub-grade level, laying non-woven geotextile directly followed by geogrid. Ballast material was then placed to a specified depth and a second layer of geogrid was placed to effectively ‘encapsulate’ this sub-ballast layer.
On this raft, or platform, further ballast was then placed to form the normal railway ballast formation.
Performance after one year is given. Details are given of other options that were considered, such as permanent de-watering of the sub-grade by pumping.
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