Stabilisation of dykes
Terrafix® needle-punched geotextiles are used to protect the coastline when used in the toe area of sea walls and dykes. They improve the construction efficiency if the sea currents cause surface erosion or unacceptable soil displacement. The three-dimensional, labyrinth-like pores and channels of Terrafix® nonwovens are not only similar to the soil structure itself, but, if correctly designed, also increase the stability of the revetment against impact stress caused by the motion of the sea. For coastal hydrodynamic forces and the typical fine to medium sands in these areas, the following simplified engineering approach can be used to determine the effective opening size 090,W of a filter geotextile when one is used below an open revetment:
090,W ≈ d50 of the subsoil
The minimum thickness of the filter geotextile should be 4.5 mm (please refer to chapter “Filtration”) in order to ensure the stability and permanency of the filter. Due to their extraordinary robustness, Terrafix® geotextiles with a mass of about 600 g/m² are used below blocks or riprap.
A geotextile with a minimum mass per unit area of 600 g/m² is necessary wherever type II (LMB5/40) or III (LMB10/60) armor rock with individual weights ≤ 60 kg are placed directly on Terrafix® geotextiles, or where concrete revetments for high-stress applications have been installed. Where individual stone weights exceed 60 kg, Terrafix® geotextiles with yet a higher mass per unit area are recommended. In the case of low-stressed dykes, Terrafix® filter geotextiles with a minimum mass of 500 g/m² and minimum thickness of 4.5 mm serve to encapsulate and stabilise the sand core from erosion. When flooding occurs, they prevent washout of the sand and ensure the stability of the dyke. Top soil as well as concrete blocks can act as an effective cover layer over the geotextile.