Infrastructure improvements (roads, railway lines and buildings) often requires making new cuttings and the steepening of embankments in loose grounds and rocks. Ideally slopes should be at a low angle of inclination to avoid compromising the stability of the area.
If this is possible, simple greening aids such as erosion control mats are usually enough to protect against washouts. These are however, not enough when steeper embankments must be secured or when there are superficial or even global stability problems.
There are a variety of erosion control mats and geotextiles available to support the greening of loose rock slopes. In principle, there are two different starting materials: synthetic geotextiles (i.e. made of polypropylene), and natural geotextiles made of organic materials such as jute or coconut fibres. Organic material products can be used for flatter slopes. In steeper slopes, synthetic products offer advantages thanks to their low weight.
Flexible slope stabilisation systems made of steel wire meshes in combination with a soil nailing system are now widely used to secure loose ground and rock slopes. These systems have proven to be very effective if applied correctly. For slope stabilization using flexible facings it is necessary to have a certain value of tensile strength to hold a bigger volume of material back together with a deformation which should be as small as possible so that no erosion problems can start and will occur. The load distribution by a local impact is much more favourable with rhomboidal meshes such as those that Geobrugg supply.
So why are Geobrugg’s products superior to the rest? Investors, designers and contractors should look at test results of products in detail to ensure that they are getting the right products with the expected performance for the job in hand. To avoid failures in installations and liability risks, it is important to make sure that the parameters in the Declaration of Performance (DoP) or European Technical Assessment (ETA) are in accordance with the corresponding design of the project. Standardisation for rockfall, debris flow, shallow landslides and slope stabilisation exists.
In the European Assessment Document (EAD) for “flexible facing systems for slope stabilization and rock protection”, several tests are described for flexible facing which have been used worldwide for decades. They are available in two different qualities: mild steel and high tensile steel wire. For both qualities of steel, in combination with soil nailing/rock bolting there exist three key characteristics for the products.
- Puncturing at the nail head plate (shearing-off resistance at the upslope edge of the spike plate)
- Slope parallel load transfer into the nail with interaction of the soil (tensile strength)
- Deformation/elongation of the mesh under load in percent
What does this mean for users?
The performance of the flexible facing is tabulated. These tables can be used to compare different products in terms of bearing resistance. Based on these tables, the three characteristics of flexible facings can be clearly defined in tender documents. Different products can be compared on a unique level.
Geobrugg is proud of the fact that many of its rockfall barriers as well as the high-tensile wire mesh systems carry the necessary certification which makes it stand out. Factory production control are well documented and evaluated to ensure compliance with the conditions laid down in the technical specifications.
Standardisation in the European Union helps to achieve a certain quality standard. The letters CE are the abbreviation of the French phrase “Conformité Européene” which literally means “European Conformity”. CE marking is a certification mark that indicates conformity with health, safety and environmental protection standards for products sold within the European Economic Area (EEA). The CE marking is the manufacturer’s declaration that the product meets the requirements of the applicable EC directives. The responsibility for the CE marking lies with whoever puts the product on the market in the EU.
There is more evidence that standard galvanized products do not stand the test of time. To achieve prolonged design life, Tecco stainless are to be considered. Stainless steel can be used for aggressive and severe environments with low pH values, close to the seashore or in areas with direct contact with salt spray. The mesh has a tensile strength of 1 650 N/mm2. When one evaluates the installation cost, replacement and maintenance of conventional systems, then the high cost of the Tecco stainless steel system is not out of line.
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.
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 recognize 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 4km 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.