Coastal protection with geosynthetics

Naue GmbH & Co. geotextile containers and geotextiles offer coastal protection with geosynthetics along the shoreline of Thorpe, England.

Through a partnership involving the Suffolk Coastal District, the U.K.’s Environment Agency and local residents, work to improve coastal defenses at Thorpeness, England, has included Naue GmbH & Co. KG Secutex Soft Rock geotextile containers and Secutex H (formerly known as Terrafix) needlepunched, nonwoven geotextiles.

In 2010 the northern part of the village of Thorpeness suffered from significant coastal erosion that damaged the existing defenses and eroded frontages. This was caused by unusual weather, including heavy storms, resulting in sand and other material erosion from the frontage, and much of the material was deposited on the Thorpe Ness (beach) itself. This exposed 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 defenses, which had suffered significant damage. This was achieved using Secutex Soft Rock geotextile sand containers—with more than 1,800 being used in total, eight to ten layers deep. Naue also supplied 21,500 square feet (2,000 m²) of Secutex H geotextiles, which were employed in a toe-shaped structure to provide added support to the gabion baskets.

J Breheny Contractors Ltd. reconstructed and strengthened the damaged coastal defenses; tide times and the weather dictated how and when the work could be carried out. Early morning starts and late evening finishes were not unusual with this project.

One advantage of soft rock containers 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.

Secutex Soft Rock geotextile sand containers are made from double-layered, mechanically bonded nonwovens, sewn with a special seam. Measuring 4.8 x 7.8 feet (1.45 x 2.38 m), they feature a white polypropylene filter layer with a mass of 18 ounces per square yard (600 g/m²) and a beige-colored protection layer (also polypropylene) weighing-in at 8.8 ounces per square yard (300 g/m²).

Maximum tensile strength of the materials is greater than or equal to 18,808 pounds-force per foot (25.5 kN/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 18,808 pounds-force per foot (25.5 kN/m).

Secutex H geotextiles work by trapping sand between the pore spaces, replicating the buffeting effects of sand without the sand being removed.

Secutex H geotextiles work by trapping sand between the pore spaces, replicating the buffeting effects of sand without the sand being removed. Manufactured from synthetic fibers, Secutex H is a staple-fiber, needlepunched nonwoven geotextile. Thanks to a 3D fiber structure, the geotextile creates labyrinth-like pore openings closely simulating the soil structure and its hydraulic properties.

The geotextile has high-water permeability, retains soil and allows root growth so that bank protection structures will blend unobtrusively with the environment. The combination of the geotextile sand containers and the nonwoven geotextile are effective for coastal protection with geosynthetics.