Two Dutch companies, Van den Herik and Boskalis/Cofra, recently won contracts for the construction of a vertical geotextile screen in the berm of the river levee along the Nederrijn, near Opheusden, the Netherlands.
Requested by the Rivierenland water board, the two companies developed their own technology to construct such a screen that is specially designed to prevent piping, a phenomenon that occurs in case of abnormally high water levels and water seeps under the levee and starts carrying sand.
Both companies got a levee section of 500 m to proof they can place a vertical geotextile screen that stops the sand transport but allows the seepage water to flow through.
On 8 July, Boskalis/Cofra was world’s first to launch its new anti-piping technology based on a geotextile screen. Van den Herik will follow with a different geotextile-based technology in two months’ time.
Growing concern over piping
The most classical way to prevent piping is by widening the toe of the levee or by constructing a very deep pile sheet wall. The Rivierenland board studied cheaper and less space consuming alternatives and started experimenting with underground screens of geotextile that stop only the sand transportation, but not the flow of the seepage.
Convinced of its potential the water board invited Dutch civil engineering companies to develop a geotextile technology for anti-piping. As a result two companies have now been invited to place their screens over a length of 500 meters. Boskalis/Cofra is now world’s first to place such a screen.
Modular system geotextile plates
Boskalis and Cofra developed a modular system of geotextile plates that can be assembled into one screen. First a trencher digs a very small trench in the toe of the levee. One by one the geotextile plates are installed and looked together in the underground.
Van den Herik developed a technology with a special designed mobile construction that houses both the trencher and the large geotextile rolls. This machine can put the screen in place continuously, making it much faster. Another advantage of this technology that it uses geotextile on a roll that can be supplied by any producer.
The water board will monitor the performance of the screens with glass fiber cables that have been attached to the geotextile. The cable measures the temperature of the seepage water and in case of a free flow the water temperature will be low. In case of a clogging of the geotextile by sand, the water flow will stop and the temperature will go up.