On Monday, 24 September 2012, Deltares started a unique experiment with geotextile on the IJkdijk in Groningen on behalf of the Rivierenland Water Authority and with co-financing from the Room for the River program. A 15 m wide and 0.5 m long GeoDetect® filter and detection system, provided by TenCate Geosynthetics, was positioned vertically in the clay layer of a test dike. The week-long test was engineered to see if this design approach could counteract piping. Sensors and water-pressure meters were used for monitoring.
GeoDetect®, a unique sensor-enable geotextile, was developed to detect and interfere with internal erosion processes within hydraulic structures; but using it to deal with piping is an entirely new application. This latest experiment at the IJkdijk has shown for the first time in the field that geotextiles can actually stop piping.
Piping has an enormous impact on the stability of a dike. It is, therefore, absolutely essential to confine this process. Previous studies have shown that it is one of the most important dike failure mechanisms. It occurs at the sand-clay interface, when water levels are high. The resulting pressure can force water to seep through the base of a dike. This water may take grains of sand with it, creating tubular openings (pipes) under the dike, which get bigger and bigger, endangering the stability of the structure. If piping is not confined, it can weaken the dike with the result that it can sag and, in the worst case, cause it to collapse.
THE EXPERIMENT
The IJkdijk is an innovative dike monitoring organization for inspection and testing based on sensor systems. The goals of the program are include to yield internationally marketable dike monitoring systems (or, smart levees) as well as more economical, durable designs that reduce infrastructure costs and rebuild needs in the water resources sector.
During September’s successful experiment, after the textile was in place the pressure on the dike was increased to induce piping. Clear piping was soon seen below the clay dike on the downflow side of the textile—but the geotextile was successful in stopping the further development of the piping channel. The geotextile stopped piping for eight days, after which the experiment was terminated.
Ulrich Förster, a Deltares dike specialist, was closely involved with the test. He is very enthusiastic about the result: “We had already conducted lab trials with the geotextile and the results were very promising. So we had high hopes for this experiment and we haven’t been disappointed. Even less sand and clay than I expected was rinsed out. We stopped after eight days because, in practice, that is usually how long high water lasts, with a risk of piping as a result.”
Now that the experiment has been successful, the Rivierenland water authority will look to see whether the textile can be tested next year on a longer section of dike in the Rivierenland area.
The Rivierenland authority has to upgrade many kilometers of dike because of the risk of piping. Traditional current measures, the widening of dikes, and the installation of sheet piling, are expensive options and take up a lot of space. A geotextile solution could be a good alternative: it is cheaper, easier to install and it doesn’t take up any extra space.
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