Geotextiles against piping
On the instructions of the Rivierenland Water Board in the Netherlands, a method has been developed to combat the sinking and breaching of dykes that result from piping: the installation of vertical sand-tight geotextile. Over the next few years, this method will be applied to a dyke in the Willemspolder. Here the sand-tight geotextile will be fitted with fibreglass sensors: TenCate GeoDetect®. The solution chosen for this project requires little space, helps to save costs, and in principle has only a modest CO2 footprint.
Water boards and the government have taken the initiative to pursue efficient innovative solutions to piping. In this situation, water flows through a quay or a dyke as a result of a huge difference in water levels and seepage occurs, leading to small tubular openings that weaken the structure. If the piping is not averted in time, subsidence or a dyke breach may be the outcome. For this reason, a research programme has been initiated: Cross-Boundary Exploration Piping. Underlying this project is the new Dutch Delta Programme, which stipulates that national flood defences must satisfy more stringent standards.
Livedijk Willemspolder is situated near the Waaldijk. Since the beginning of October 2015, approximately 100 metres of the summer quay has been fitted with vertically installed geotextile as a preventive measure. Geotextile is a sustainable material that can be effectively applied in dyke improvement.
For decades, it has been used worldwide for the erosion protection of flood defences. In principle, it has a low CO2 footprint. The geotextile installed as a filter in the dyke body allows water to pass through, but not sand. As a result, no sand boils occur and no seepage takes place. The simultaneous application of fibreglass sensors to the geotextile means the effects of piping at high water and the stability of the dyke can be monitored.
It is hoped to observe in the Willemspolder how piping develops and how the transport of sand proceeds. This will contribute to acquiring both a better understanding of piping and insight into the positive effects of the installed geotextile. Over the next two years, measurements will be carried out during periods of high water.
‘We’re hoping for winters with high water, otherwise progress will be sluggish and then we’ll have to extend the test period,’ says Frans van den Berg, coordinator of the Rivierenland Water Board Dyke Reinforcement Programme. According to him, piping is a problem that is underestimated - even in the Netherlands. ‘A great deal has to be done in terms of reinforcement because of the new standards, particularly in the river area. The choice fell on the Willemspolder outside the dyke because quite a lot of piping occurs there. Normally, embankments are created but this entails considerable space and earthworks.’ As the vertical sand-tight geotextile requires little space, the feasibility of dyke improvements is increased and the solution is cost effective to boot.
Vertical sand-tight geotextile is applied on the inside of the dyke. Water can pass through freely, but sand is blocked. TenCate Geodetect® applied as vertical sand-tight geotextile won the Dutch Water Innovation Award in the category Dry Feet in 2013.