Armater geosynthetic material specified for Temple Wood cutting, CTRL Contract 330

15/08/2000

The construction of the Channel Tunnel Rail Link (CTRL) through Kent requires the excavation of several deep cuttings. Working with the CTRL Contract 330 main contractors Alfred McAlpine/Amec JV, Maccaferri Ltd, specialists in retaining structures, slope reinforcement and erosion protection, has supplied the Armater cellular containment system to support the soil and vegetation on the sides of the cuttings.

Armater has been supplied to the Temple Wood cutting, near the River Medway. Located in poor ground, the cutting features an upper slope gradient of 1:2.5 through superficial deposits with a 1:1 gradient over an eight metres high lower slope. The lower slope in chalk contains clay infilled solution features. To ensure overall stability of the clay material, soil nailing has been used with Armater secured to the slope surface.

Matt Showan, design engineer at Maccaferri recommended the Armater product to the geotechnical engineer for the main contractor. Armater was proposed as the slope surface finish to secure the topsoil layer and prevent erosion and the development of water paths as a result of run-off following heavy rainfall.

Lightweight, flexible and easy to install, Armater forms cells into which topsoil is placed. These cells reduce the erosion caused by surface run-off and prevent the formation of gullies. The porous material enables water to flow slowly thought the hexagonal cells, avoiding ‘ponding’ at the base of the cell.

The JV geotechnical engineer was particularly impressed with the non-woven material used in the manufacture of Armater. He commented: “It is sufficiently rigid to hold soil and vegetation in place, while the porous nature of the material allows water to drain away without drain holes which can become blocked and create problems. In addition, the material is more homogeneous with the soil and will facilitate rapid re-vegetation.”

The Armater was laid on completion of the soil nailing and secured to the slope surface using 0.5m long, 10mm diameter steel pins and buckles at 1.0 metre centres. Providing technical support and back up, Maccaferri Sales Engineer, Tim Parsons was on-site to oversee the initial work. On completion of the Armater installation, a 360o excavator was employed to place the topsoil in the cells and finished off by hydroseeding.

The UK subsidiary of an Italian-based engineering company, Maccaferri Ltd specialises in 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 supported by three designers and a technical director. Maccaferri also retains a full-time bio-engineer providing advice on environmental issues and ensuring that, where appropriate, all engineering solutions support plant growth and create a ‘greener’ and more attractive landscape.

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