1.4.06 Integrated warning system – monitoring and stabilising dykes with sensor-based geotextiles

The condition of dykes has almost exclusively been monitored visually up to now. With the appearance of their insides hidden from inspectors, damage is often not noticed until it is in the advanced stages. This means it is generally too late to implement targeted support for sections at risk of breaching in crisis situations. Automated monitoring within the dyke could prove to be helpful here: with funding from the BMBF, the Saxon Textile Research Institute (STFI) has worked together with the Federal Institute for Materials Research and Testing (BAM) and other partners to develop special geotextiles that both secure and monitor dykes at the same time. In the meantime, the research has produced a new spin-off company called fibrisTerre GmbH as well as three marketable patents.

Conventional dyke inspections in Germany monitor the surface and are not always able to detect damage with sufficient speed or reliability. Round-the-clock monitoring would be required during times of flooding, and this is hardly feasible from a manning perspective. There are actually electronic measuring systems already available on the market, but they are expensive and as such are rarely used. Cue the BMBF-funded research project entitled “Entwicklung von multifunktionalen, sensorbasierten Geotextilien zur Deichertüchtigung, für räumlich ausgedehntes Deichverteidigung-Monitoring sowie für die Gefahrenerkennung im Hochwasserfall bei der Deichverteidigung” (development of multifunctional, sensor-based geotextiles for reinforcing dykes, dyke monitoring over greater areas and hazard detection to defend dykes in the event of flooding). Scientists from the Saxon Textile Research Institute in Chemnitz worked together with the Federal Institute for Materials Research and Testing in Berlin and other partners to develop an innovative material with built-in sensor technology as a part of this project.

Geotextiles: a versatile construction material

Geotextiles are heavy-duty fabrics specially designed for outdoor use; they can be made of woven, non-woven or knitted fabrics, and from natural or synthetic materials. They are used within geotechnical and structural engineering – generally to stabilise ground constructions and prevent soil erosion, e.g. in constructing roads and railways or waterways and dykes. Depending on their purpose, geotextiles are either permeable – when installed on steep slopes, berms or embankments – or impermeable, e.g. when used at landfill sites.

Automated dyke monitoring

The idea behind the project was to develop a multifunctional geotextile that, as well as being able to secure the dyke slopes, could also be used to monitor dyke stability. Fibre-optic sensors were therefore incorporated into nonwoven structures during the manufacturing process itself to serve this precise purpose. These sensors feature the standard, low-cost glass fibres used within telecommunications and use special optical measuring procedures to detect even minimal stretching of the textile structure as well as temperature fluctuations so that dyke deformities can be registered during a flood. The detected changes can then be routed to central measuring and monitoring stations, where they can be called up at any time so that the alarm can be raised promptly in the event of any damage.

A new basis for measuring devices was developed for obtaining and evaluating the readings, work primarily undertaken by the BAM. Based on Brillouin frequency range analysis, the new measuring technology developed and patented during the BMBF’s RIMAX project (Risk Management of Extreme Flood Events) clearly had so much potential that the EXIST research transfer programme approved the application of three young scientists to set up their own company. Founded in January 2010, fibrisTerre GmbH is the first spin-off company from the BAM.

Producing the geotextiles

How should textiles be made in order to ensure sufficient protection of the optical fibres? Which materials are most suitable? How can the glass fibres be worked into the textile? To answer these questions, the scientists at the Saxon Textile Research Institute conducted numerous tests on a non-woven Raschel machine. The method used is a conventional production procedure for geotextiles that has been specially modified for this purpose; new test methods have also been developed to determine the sensor and mechanical performance profile of the multifunctional geotextiles. The STFI is obtaining patents both for the production process and for the use of geotextiles with built-in sensors within dykes.

In the meantime, the functional capability of the geotextiles has been demonstrated in various field tests. Various studies using a trial full-size dyke on the premises of the Franzius Institute of Hydraulics, Waterways and Coastal Engineering at the University of Hanover have shown what the new procedure can achieve. Simulations of different crises and loads were run, proving the functional capability of the sensor-based geotextiles under conditions of practical relevance. BBG-Bauberatung Geokunststoffe GmbH is currently working on marketing the sensor-based geotextiles together with rg-research, which was founded by Rainer Glötzl (http://rg-research.de/english/).

Benefits of the procedure

Comparatively speaking, sensor-based geotextiles are a cost-effective alternative to other dyke monitoring approaches. The optical procedure lowers the costs per measuring point considerably, and provides data for the entire area rather than just isolated spots or along a chain of sensors. This also makes it possible to monitor extremely long sections of dyke with little personnel expenditure and enables precise mapping of damage. Only a monitoring system enables observation of both short-term changes such as cracks and scouring and long-term effects such as dyke subsidence. Finally, the procedure is also financially beneficial when it comes to constructing dykes, as securing the structure and integrating the monitoring system becomes a single-step process.

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1.4.07 Building security for all

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1.4.05 Avoiding dyke breaches