Safe coastal protection with geosynthetic sand containers
Coastal erosion rectified
In a scheme that has resulted from a partnership involving Suffolk Coastal, the Environment Agency and local residents, work to improve coastal defences at Thorpeness has included the supply of Secutex® Soft Rock containers, and Secutex® H geotextile (formerly known as Terrafix®) needle-punched nonwoven from NAUE.
It was back in 2010 that the northern part of the village of Thorpeness suffered from significant coastal erosion which damaged the existing defences and eroded frontages. This was caused by unusual weather, including heavy storms, resulting in sand and other material being removed from the frontage, and much of the material being deposited on the Ness itself. This resulted in the exposure of a series of rock-filled gabion baskets that had been in place since the mid 1970s.
Strengthening work needed to be carried out to support the gabion defence which had suffered significant damage. This was urgent as it was felt the gabion structure might not offer the necessary level of protection in the months ahead and was achieved using the NAUE Secutex® Soft Rock geotextile sand containers – with over 1800 being used in total, eight to ten layers deep. NAUE also supplied about 2000m2 of Secutex® H which has been employed in a toe-shaped structure to provide added support to the gabion baskets.
Work carried out by J Breheny Contracting Ltd. has included the reconstruction and strengthening of damaged coastal defences at the northern end of Thorpeness – with tide times and the weather dictating how and when the work could be carried out. Very early morning starts and late evening finishes were not unusual with this project. There are a number of significant advantages with soft rock containers. One of these is that they arrive on site empty – greatly reducing the transportation demands, with significant knock-on cost and environmental benefits.
They are then filled with material on site using sand from the beach, eliminating the need to supply raw materials.
The Secutex® Soft Rock geotextile sand containers are made from double-layered, mechanically bonded nonwovens, sewn with a special seam. Measuring 1.45m by 2.38m, they feature a white polypropylene filter layer with a mass of 600g/m2 and a beige coloured protection layer (also polypropylene) weighing-in at 300g/m2. This total mass of 900g/m2 emphasises the delivery and handling advantages these containers offer.
Maximum tensile strength of the materials is greater than or equal to 25.5kN/m in both machined direction and cross machine direction, while the elongation at the maximum tensile strength is at least 50% in machine direction and 30% in cross machine direction.
There is no weakness at the seam – it retains the maximum tensile strength figure of no less than 25.5kN/m.
Secutex® H works by trapping sand between the pore spaces, replicating the buffeting effects of sand without the sand being removed.
Manufactured from synthetic fibres, Secutex® H is a staple fibre needle-punched nonwoven geotextile. Thanks to a three-dimensional fibre structure, it is able to create labyrinth-like pore openings closely simulating the soil structure and its hydraulic properties.
Secutex® H has high-water permeability, retains soil, and allows root growth if needed so that bank protection structures will blend unobtrusively with the natural environment. Secutex® H boasts more than 30 years of successful non-woven geotextile applications in hydraulic engineering – proving the high technical standards and abilities of this product. Secutex® H stands out for its versatility, filter stability, and resistance to abrasion.
Elongation at maximum tensile strength is about 70% in machine direction and 30% in cross machine direction – ensuring the sheet copes with the load without splitting, instead the material stretches.
Once again NAUE Geosynthetics has provided a solution to a problem that required a speedy and effective response. This is one of many coastal erosion projects around the UK, and the World, that is benefitting from NAUE Secutex® Soft Rock containers, and the Secutex® H needle-punched nonwovens for hydraulic engineering.