The HS1 High Speed Line, formerly known as the Channel Tunnel Rail Link, passes through a range of terrains. At one point the track passes over the mid Kent downs and in order to provide the required track level when the route was constructed, steep cuttings, some 350m long and up to 12m deep were excavated through the chalk.
The cuttings were dug into structurally sound chalk with slope angles that ranged between 45° and 50°. Since the natural steep slope of the chalky face was unable to support any plant growth, the cuttings would have presented a stark and unacceptably barren appearance along the line. The planning consent for the CTRL was dependent on minimum impact on the unique Kent chalk land ecosystem. It was essential that the contractor created an environment that would give rise to the establishment of vegetation over the chalk face.
The contractor opted to use ABG Erosaweb to hold a topsoil cover in place on a steep chalk face and ABG Erosamat for slope protection and root zone reinforcement on the surface of the less steep cuttings between 30° and 40°.
The Erosaweb geocellular honeycomb soil confinement system was laid on top of the steep chalk face and secured with mild steel J pins into the chalk. The contractor drilled holes prior to fixing.
The cells of the Erosaweb geocell that hold the topsoil in place on the steep chalk face provide sufficient soil containment to support good moisture retention for the roots of vegetation, thus maintaining grass cover, even during dry periods.
Erosamat erosion control matting’s three-dimensional open matrix was utilised to protect the less steep upper slopes from erosion and to provide permanent root zone reinforcement for the vegetation. 150mm of topsoil was placed on the chalk with the 20mm thick Erosamat geosynthetic pinned on top.
The topsoil was hydro seeded with a drought resistant seed mixture. Even before the tracks were laid, an excellent cover of grass had established over the face of the chalk The natural regeneration of the wildlife ecosystem on the slopes will play its part in helping to reduce any adverse environmental impact of the cuttings.
ABG Erosamat erosion control for railway embankments
The ABG Service
ABG offered a design and installation advice on the optimum pinning centres for the given slope, with advice on filling sequence of cells and final hydroseeding.
Contact ABG today to discuss your rail or erosion control specific requirements and discover how ABG past experience and innovative products can help on your project.