In some cases, dykes alone are insufficient for coastal protection. Structures such as groynes, breakwaters and sea walls are used to prevent the erosion of coastal areas and directly influence the localised sea currents. Terrafix® sand mats provide stability as well as scour protection for these structures. Even in deeper waters, the underwater installation of Terrafix® B 813 is easy due to the integral sand ballast layer. Depending on the subsoil conditions, Terrafix® filter layers that are at least 4.5 mm thick (for soil types 1 to 3) or 6.0 mm thick (for soil type 4), ensure the filter stability of the fine grained subgrade. Secugrid® geogrids are used as additional reinforcing elements where foundation failure is possible.
The reinforcement measures required for transverse structures depend on the prevailing sea current stresses to which they are subjected. For low-current stresses, a Terrafix® needle-punched nonwoven geotextile or a Terrafix® sand mat can be placed on the sandy dam core and covered with riprap. For mediumcurrent stresses, it is recommended that the dam core is reinforced with two or three layers of Terrafix Soft Rock® sand containers prior to installing the revetment. Groynes can be built entirely with Terrafix Soft Rock® sand containers, and if required, be covered with the appropriate revetment.
Terrafix Soft Rock® sand containers consist of needle-punched nonwoven geotextiles with a maximum tensile strength of ≥ 30 kN/m. Over 80 % of the nonwoven geotextile strength is required for all seams. One of the remarkable features of Terrafix® is its robustness and elongation capacity. Terrafix Soft Rock® sand containers can be placed in their exact position and over granular terrain without a high risk of becoming damaged by using specific excavator grabs (“grippers”).
When properly designed, even the dynamic impact of dumping does not reduce the performance of Terrafix Soft Rock® due to the flexibility of the Terrafix® nonwoven geotextile. Mussels, algae and other underwater life attach to the crimped fibres that are partially in a vertical position, so that the Terrafix Soft Rock® sand containers integrate quickly and easily into the sensitive sea ecosystem.