Reinforced soil embankment to absorb high energy impacts along the regional road SR 47 Aymavilles-Cogne, Aosta (Italy)

Alberto Grimod, Valerio Segor

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Landslides and Geohazards

ABSTRACT: Reinforced soil embankments represent very powerful solutions as passive rockfall mitigation systems. They are used worldwide to protect infrastructures and residential areas against rockfall, debris flow and avalanche phenomena. The paper presents a case study of three reinforced soil embankments designed to stop energies higher than 25,000 kJ along the regional road SR 47 Aymavilles-Cogne, in the Aosta Valley Region (Italy). The rockfall embankments design has been carried out by the Department of Hydrogeological Setting of Mountain Basins - Aosta Valley Region. The structures have been designed using innovative formulations and the new calculation approach defined by Maccaferri and the Polytechnic of Turin. All the design steps, as well as, the construction phases, the effects of impacts against one of the structures and its consequent maintenance will be described.

RÉSUMÉ: Les merlons en remblai renforcés sont des systèmes très efficaces pour la mitigation passive contre la chute de pierres. Ils sont utilisés dans le monde entier pour protéger routes et habitations situées en proximités de zones à risque de chute de pierres, éboulements et avalanches. L™article présente un cas d™étude de 3-merlons para-blocs en remblai renforcé qui ont été installés pour protéger la route régionale SR 47 Aymavilles-Cogne, Région Vallée d™Aoste (Italie). La conception des structures a été faite par le Département de l™Aménagement Hydrogéologique des Bassins Versants- Région Vallée d™Aoste. Les structures ont été conçues en utilisant les formulations et la nouvelle approche de calcul défini par Maccaferri et le Polytechnique de Turin. L™article décrit en détail le design, les phases d™installation et les effets des impacts contre l™une des structures, et le conséquent entretien. 1 SOIL REINFORCED ROCKFALL EMBANKMENTS Rockfall embankments are commonly used to protect roads, railways, mining and residential areas against rockfall, debris flow and avalanche events. These structures are classified as passive systems, because they are installed at a certain distance from the detachment area. Thus, their goal is to intercept unstable masses (rock, debris, snow, etc.) that can fall or slide from a certain area located up-slope. This category typically includes also rigid and deformable rockfall barriers, as well as debris flow and hybrid fences. It is possible to group the passive rockfall mitigation systems in three main categories depending on the energy absorption that are able to withstand (Grimod et al., 2013): i) Rigid Rockfall Barrier up to 100 kJ; ii) Deformable Rockfall Barrier from 100 kJ, according to ETAG 027 (EOTA, 2008), up to 8,600 kJ at the present (in accordance with ETAG 027:2008); and iii) Rockfall Embankments up to 25 MJ. Different types of rockfall embankments can be designed (Ronco et al, 2009): 1. Ground embankment: made of selected and compacted natural ground, with trapezium shape and inclined faces (on both size) at about 35-40°; 2. Embankments built with huge rock blocks: the inclined faces are usually equal to 60-70°; 3. Unreinforced ground embankment with a face made of wire mesh gabions: the gabion side inclination (upslope) is about 90°, the other side is about 35°; 4. Embankment made totally with gabions; 5. Embankment reinforced with wood elements; 6. fiUmbrellafl structure filled with soil: usually for temporary works; 7. Reinforced ground embankment, made of compacted soil with reinforcement and absorbing mattress on the mountain side face; 8. Reinforced soil embankment, made of compacted soil with reinforcements (i.e. geotextiles, geogrids, metallic wire nets), with trapezium shape in cross section and faces inclination at about 60 to 90°. Rockfall embankments may provide several advantages over rockfall fences, such as (Brunet et al., 2009): - Energy absorption higher than 8,600 kJ; - Resistance to multiple impacts; - Negligible downslope deformation after the impact; - Ability to intercept high speed impacts (> 30-40 m/s); - Reduced and easy maintenance after impacts; - High durability also in aggressive areas; - Easy and rapid installation;

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