MACMAT™ -R, BIOMAC™, ROCKFALL NETTING AND GABIONS PROVIDE SOIL REINFORCEMENT AND EROSION PROTECTION
A range of geosynthetic solutions and gabions from Maccaferri Ltd, specialists in retaining structures, soil reinforcement and erosion protection, have been specified to stabilise the sides of the Kilmacud cutting, part of Dublin’s LUAS light rail transport system. Currently under construction, when complete the new system will provide the city with three tramlines linking central Dublin with the surrounding area.
The new tramway, powered by overhead electricity lines, will operate within the existing road system.Where possible, however, outside the city centre lines have been routed along existing disused rail tracks. Once part of an old suburban line, the Kilmacud cutting, located in the Dundrum suburb of Dublin is on Line B, running from St Stephen’s Green in central Dublin to Sandyford industrial estate.
Long disused, the cutting required considerable widening at the base to accommodate modern tram technology and overhead power lines. Running through a built-up area, widening the crest was not an option. Cutting back and creating steeper gradients within the existing rock and soil side slopes was the only way to create the additional space.
To reinforce the steeper side slopes of the cutting, geotechnical consultants John Barnett & Associates worked closely with project track and civil works designers Sinclair Knight Merz. A range of Maccaferri soil reinforcement solutions were developed to stabilise the different slope gradients within the cutting.
Comprising of both rock and soil strata, the Kilmacud cutting is approximately three kilometres long, with slope heights ranging from 2 – 11 metres and gradients of between 600 – 850 % through rock and 150 – 450 on the soil covered sections. Slope stability analysis was undertaken to determine optimum gradients.
MacMat-R was specified for steeper slopes where soil reinforcement was required in addition to erosion control. A composite material combining Maccaferri’s unique double twist hexagonal wire mesh with a three dimensional geomat manufactured from entangled, heat bonded polypropylene monofilaments, MacMat-R provides a three dimensionally stable matrix for vegetation, the additional strength of the wire mesh offering additional soil reinforcement.
Used to stabilise steeper slopes, where soil overlays rock strata, MacMat-R has been combined with rockfall netting. On less steeply sloped areas, BioMac degradable quilted coir soil blankets have been specified to control soil erosion, enabling newly planted grass seed to grow through the protective blanket. Very shallow slopes have been re-planted with vegetation.
In addition, a number of small gabion walls have been specified adjacent to the trackside. With speed of construction being a key factor, gabions were preferred to reinforced concrete retaining walls. Designed and supplied by Maccaferri, a number of walls have been constructed, ranging from 8 – 20 metres in length and two to four metres high.
The Kilmacud cutting is due for completion this summer. Working up from the south and towards the city centre, specialist sub-contractor, Ritchies is installing the various Maccaferri products as excavation is completed. Construction of the whole LUAS light railway project is been overseen by AMB Joint Venture.
The UK arm of the Maccaferri Industrial Group, headquartered in Italy, Maccaferri Ltd specialises in gabions, geotextiles, geogrids and geomats. In addition to a full range of products for retaining structures, soil reinforcement and erosion protection, the company offers an in-house construct, design and consultancy service.