Construction World September 2019

Debris flow barriers Flexible ring-net barriers had been introduced more than 10 years ago as a solution to protect against debris flow. Since then, more than 250 debris flow barriers have been installed in more than 25 countries to protect infrastructures such as roads, railways or residential areas from significant damage. In the Western Cape, on Chapman’s Peak in Hout Bay, a total of five debris flow barriers had been installed in 2015 to stop further debris flow from reaching the picturesque road. These were the first debris flow barriers that had been installed on the African continent. Local consulting firm, Melis & du Plessis did the geohazard assessment on Chapman’s Peak, while contractors Penny Farthing did the installation work. Both companies convinced the Western Cape Government to make use of Geobrugg’s geotechnical solutions. The suitability of the debris flow nets for small volumes as well as for very large volumes with several nets in succession was proven in large field tests. Systems can be measured using the freely accessible DEBFLOW software of Geobrugg. Major advantages of flexible debris flow barriers are their low weight and short installation time. This is important in steep, difficult terrain where access for large construction machinery would be uneconomical. On Chapman’s Peak, the contractors could use an old South African National Parks road at the top of the slope to transport most of the machinery to the top of the slope. From there it was then carried down to the work face. The system is made in smaller, manageable sections that could be carried to the work face where it was assembled. The Geobrugg system aims to eliminate unnecessary drilling of holes. This design reduces the construction costs by keeping drilling to a minimum. Due to their low visibility, debris flow nets are used increasingly more. Especially in environmentally sensitive areas such as the picturesque Chapmans’ Peak Drive, this is a decisive factor and cost-effective alternative to conventional situations all over the world. Geoprevent In partnership with Geoprevent who have been developing and installing alarm and monitoring solutions for natural hazards for many years, Geobrugg can now offer monitoring of hazard zones. These warning systems recognise precursors to events. These

enable measures to be taken in good time (i.e. road closures). Alarms systems recognize the event itself. Alerts take place in real time so immediate protection can be guaranteed. These monitoring units can be applied to measure rockfall movement on rockfall drapes and on rockfall barriers. Real time detection of debris flow and landslide movements are also possible. Detection of avalanches (tracking/ mapping) is also done. A monitoring unit is a system that consists of various components. The systems are built to stand up to harsh environmental conditions. Measurements are done by radar, cameras, laser and other technologies. Radar works reliably in all visibility conditions and is used for various applications. Detection of events up to 4 km is possible with real-time alerting. LIDAR Laser measures rock face surfaces or landslide events with mm precision. The monitoring systems can operate when there is no mains power. Alternative power supplies are in the form of solar cells, fuel cells with methanol, batteries or wind/water turbines. Webcams and optical deformation analysis of the surface monitor landslides or rock movements. Webcams are remote controllable while high resolution enables detailed assessment of the area. Communication systems for data and alarm transmissions can be done with GSM (mobile radio), WiFi, radio, glass fibre, etc. It is recommended that two communication channels are used for alerts for redundancy reasons. Besides the direct impact of monitoring systems, it also offers other economic benefits about the availability of infrastructure. Monitoring measures can make a decisive contribution to safeguarding housing, traffic, routes, tourist destinations or industrial sites. Tracking and mapping of events are done with remote monitoring. The monitoring supplies valuable information such as location of unstable zones, movement speeds and direction, event frequency and estimate of the volume of unstable zone. It is an ideal supplement to installed measures for monitoring large infrequent events. Geoprevent’s monitoring solution offers a cost-effective solution to increase safety. It has a low maintenance costs and a low environmental impact. Cost-efficiency is also established with shorter closure times of transport routes, infrastructures etc. Examples of such monitoring systems are in Switzerland and Norway. 

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CONSTRUCTION WORLD SEPTEMBER 2019