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Geosynthetics combine to create stiffened trackbed in Scotland

Case Studies | October 25, 2021 | By:

Photograph courtesy of Greenfix UK and Presto GeoSystems

The Borders Railway is the longest new domestic railway to be constructed in Britain in more than 100 years. Four new stations in Midlothian area and three in the Scottish Borders region have reduced journey times between Tweedbank and Edinburgh to less than one hour from nearly two and one-half hours.

The area approaching the new Galashiels station at Fountainhall was found to have particularly wet and marshy peat ground requiring additional stabilization beyond the conventional geosynthetics routinely used in trackbed construction. The Presto GeoSystems GEOWEB 3D confinement system, successfully employed in the rail industry for more than 30 years for challenging soil-stability problems, was chosen to stabilize this area of the track. The GEOWEB material carries the U.K.’s Network Rail approval for track drainage with Parts and Drawings System (PADS) numbers covering 4-inch, 6 inch and 8-inch (100-mm, 150-mm and 200-mm) depths.

Greenfix UK, a leading designer and supplier of soil stabilization and erosion control systems in the U.K., worked with the main contractor, BAM Nuttall Ltd., a construction and civil engineering company that often works with the rail industry, to establish the most appropriate grade and depth of the GEOWEB 3D system to perform with the exceptionally soft ground conditions. The GEOWEB system’s ability to perform in soft subgrades and suitability for this type of application was supported by test results from the Transportation Technology Center in Colorado.

Design phase

Design work was performed by Greenfix UK in conjunction with local track engineers. The use of the GEOWEB 3D system would create a stiffened ballast layer and reduce ballast depth requirements by at least 50%. Two layers of 6-inch (150-mm) GEOWEB material were selected as the most suitable depth for this challenging site.

Installation of the ballast reinforcement system

A geotextile separation layer and geogrid reinforcement layer were laid over the prepared aggregate base, followed by another layer of aggregate. Next, GEOWEB panels were expanded and positioned two panels high and two panels wide across the trackbed to cover a width of 5.2 meters 17 feet (5.2 m).

GEOWEB sections were installed end-to-end and side-to-side with turn-and-lock ATRA Keys. The connection keys are fast and easy to install—and assure a secure connection at each GEOWEB joint for optimal performance.

ATRA Keys are also permanent connections—3X stronger and faster to install than stapling, and safer. Made from corrosion-resistant polymer, ATRA keys will not degrade over time.

About Greenfix UK

Greenfix UK’s technical staff provided technical support to the designers and client as required and were on-site to train and advise the contractors responsible for the installation. (Project information and material supplied by GREENFIX UK.)

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