18/06/2001
Maccaferri Ltd, specialists in retaining structures, erosion protection and slope reinforcement, has recently completed work on an embankment on the main Glasgow-Edinburgh rail link. Gabions supplied and installed by Maccaferri Construction Ltd, have been used to reinstate and stabilise the slope, reducing the amount of engineering work required and ensuring the work was completed on schedule.
Located in a narrow, steep-sided gully/ravine approximately 200m east of Polmont railway station, on the section of line between Linlithgow and Falkirk, the gabions replace an old masonry retaining wall.
Speed of installation was a key factor in determining the preferred engineering solution. Railtrack’s main contractors, Glasgow-based First Engineering appointed Maccaferri to act as sub-contractors and Donaldson Associates Ltd as designers.
Ken Millin, Project Services Manager at First Engineering, comments: "Obviously, safety is the first priority in all our work for Railtrack. However, we must also bear in mind the inconvenience to the travelling public resulting from a lengthy line closure. Maccaferri Gabions are a well-proven product and are readily available for immediate installation, offering the optimum solution. We allowed for the line to be closed for a week, and were able to re-open the track right on schedule."
With speed of the essence, Maccaferri’s Area Engineer, Alan Blair worked closely with First Engineering’s Consultants, Donaldson Associates and Railtrack to develop an effective solution. The resulting design was then checked using Maccaferri’s custom-designed GAWAC software, a programme developed specifically to analyse the stability of mass gravity Gabion walls. This allows consideration of geometry, loads and other factors with the option of visualising drawings of the wall, upstream soil and external loads.
The solution provided for a Gabion wall of 4 metres in height, with a length of 16 metres and an additional low height wall extending for a further 20 metres. An unusual feature was the provision of prefilled Gabions to make up the lower courses of the new wall, essential to overcome practical problems resulting from the exceptional amount of water in the burn.
The remainder of the wall was completed using conventional ‘flat pack’ PVC coated hexagonal woven mesh Gabions erected on-site and filled with 100mm – 200mm stone. This method of construction is ideal for ‘difficult’ locations with limited access and the site at Polmont, a deep ravine in a built-up area, presented a severe challenge in terms of access.
Working ‘round the clock’ Maccaferri Construction Ltd employed two teams working in shifts to complete the job in less than the time allocated by Railtrack, allowing the line to be re-opened on schedule.
Box Gabions are rectangular units fabricated from a double-twist, hexagonal mesh of PVC and Galfan coated steel wire. Galfan is a 5% aluminium/zinc mischmetal which provides enhanced corrosion protection characteristics when compared to conventional galvanising.
The standard size for each Gabion is 2m x 1m x 1m with a fixed diaphragm at 1m, but alternative sizes may be specified to meet precise specifications. Supplied folded flat, units are laced together using continuous 2.2mm diameter lacing wire, or alternatively high tensile steel fixing rings can be attached using a special pneumatic assembly tool. Once assembled, each unit is filled with natural local stone to create a retaining structure which is in sympathy with the surrounding environment.
The UK arm of the Maccaferri Industrial Group, headquartered in Italy, Maccaferri Ltd specialises in soil supporting systems including gabions, geotextiles, geogrids and geomats. In addition to a full range of products for retaining structures, slope reinforcement and erosion protection, the company offers an in-house design and consulting service and a design and construct service.
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