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After a landslide displaced 500 cubic meters of material, Redi-Rock pre-cast modular blocks provided a cost-effective and speedy solution to re-open the road into Andorra one week ahead of schedule.
Tucked amidst the Pyrenees Mountains near the border of France sits the little ski town of Pas de la Casa, Andorra. The town is reliant on tourist traffic year round to keep its economic engine running, so when a landslide closed one of only two roads into the principality at the end of April 2019, the community needed a solution to re-open the road fast.
The landslide on RN 22 -- which was 100 meters (328 feet) wide, 30 meters (98 feet) high, and 20 meters (65 feet) deep -- had displaced 500 cubic meters (654 cubic yards) of earth and rock near the bridge of La Mina. Estimates were that if the situation wasn’t stabilized as much as 3,000 cubic meters (3,924 cubic yards) of rock could fall on RN 22.
With the town virtually cut off from the outside world and their local economy in jeopardy, the French Department of Roads for the Southwest brought in STAM, a company that specializes in difficult to access sites in high-altitude, mountain environments.
STAM mobilized a team of five excavators to work round the clock removing debris from the steep terrain at 1,800 meters (5,905 feet). Once the land was stabilized and the debris removed, the next step would be installing a retaining wall to shore up the slope. For that task, STAM director Jeans-Marie Tissot reached out to Jean-Michel Morello, owner of AL Rock/Gedimat Vialleix, a licensed Redi-Rock supplier.
Having worked together before, both Tissot and Morello knew that using Redi-Rock large precast modular blocks (PMBs) to construct a wall would be a faster, more cost-effective solution than the proposed cast-in-place wall. Morello got to work coordinating with the network of Redi-Rock suppliers in France known as ML Rock. Three ML Rock producers -- AL Rock, BBLOX/Lachaux Betons, and Carrieres et travaux de Navarre -- worked together to analyze their inventory of 1520-millimeter (60-inch) blocks, determining how to supply the 430 blocks necessary for the emergency repair.
In addition to being able to supply the blocks on short notice, the quick installation process for Redi-Rock was a huge benefit in this emergency repair as well. Weighing up to 2,190 kilograms(4,840 pounds), Redi-Rock blocks are machine set, and the patented knob and groove technology allows the blocks to be easily installed with a precise setback or batter. The blocks already have a natural stone texture when they leave the factory, so there’s no additional finish work necessary onsite.
After the Redi-Rock base course is set, a typical crew of two to three men and a piece of lifting machinery, such as an excavator, can set upwards of 65 square meters (700 square feet) a day.
In the case of the wall along RN 22, STAM finished the entire project -- over 267 square meters 2,875 square feet) -- in just four days.
In total, 33 delivery trucks supplied the 689,000 kilograms (760 tons) of Redi-Rock PMBs to craft the wall. AL Rock supplied 200 blocks from their location in Bort-les-Orgues, France, which was 500 kilometers (310 miles) from the site of the repair. Manufacturers will typically ship Redi-Rock approximately 200 kilometers (125 miles), but despite being 2.5 times the standard shipping radius, the PMB solution with Redi-Rock was still a more cost-effective solution than the cast-in-place alternative in this case.
The finished Redi-Rock wall, which curves along the roadway and stretches 80 meters (262 feet) long and 3 meters (10 feet) tall, was finished a week ahead of the envisioned schedule for the project. RN 22 was closed for 18 days, but thanks to the technical ability of STAM and the availability and quick install of Redi-Rock, the road is now reopened and safe for traffic.
To learn more about solving earth retention problems with Redi-Rock, check out the International Design Resource Manual.
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