Adelaide Rail Network embraces latest technology

The Project

Tracksure, a joint venture between John Holland, Coleman Rail and York Civil, was awarded the Adelaide Metropolitan Rail Revitalisation project by the Department of Planning, Transport and Infrastructure in South Australia (DPTI).

The revitalisation forms the centrepiece of a $2 billion investment transforming the metropolitan passenger rail network. The project involved a major upgrade of several of the network assets including two primary sections, the Gawler & Noarlunga lines.

This large and complex project required a similarly complex formation design which required subgrade improvements where marginal soils had deteriorated.

The Solution

Global Synthetics (along with its German manufacturing partner Naue GmbH) was approached to offer a suitable method of improving the strength of these existing marginal subgrades using advanced geosynthetic materials.

The design team chose Secugrid®, an ultra high modulus geogrid specifically designed to increase the effective shear strength and bearing capacity of foundation soils for road and rail applications.

The Secugrid® was selected against a range of different materials on the basis of its technical characteristics and proven performance.

The Result

Secugrid® allowed the client to avoid the expensive exercise of excavating and replacing the existing weak subgrade. Traditionally, geogrids have been utilised successfully when located between the existing weak subgrade and structural overburden. However, for this project, the project design team required Secugrid® 30/30 to be placed directly below the renewed primary ballast formation (see diagram).

One of the critical design criteria was to ensure the chosen geogrid had the required aperture size to satisfy the necessary ‘interlock’ dictated by the 40-50mm ballast stone.

The structural ‘bars’ of Secugrid have the ability to ‘rotate’ under confinement which enables it to bond with a broad range of interface stone sizes.

To achieve separation and filtration below the ballast, the Secugrid® was underlain by a 500g/m2 nonwoven geotextile. The ProFab® geotextile was selected on the basis of its inherent suitability in applications where cyclic load conditions exist.

ProFab® is manufactured using staple fibre technology which carries superior abrasion and puncture resistance - qualities which are paramount in rail, pavement and rock armoured applications.

Approx 275,000m2 of Secugrid ®30/30 & ProFab were supplied for this project which was completed in 2013.