Feb 01, 2021

Retaining Wall System Aids in European Landslide Repair

The landslide – 328 feet wide, 98 feet high, and 65 feet deep – displaced 654 cubic yards of earth and rock near the bridge of La Mina in France.

The landslide – 328 feet wide, 98 feet high, and 65 feet deep – displaced 654 cubic yards of earth and rock near the bridge of La Mina in France.

Tucked amidst the Pyrenees Mountains on the border of France and Spain sits the small ski town of Pas de la Casa, Andorra. The town and its ski resort, economically reliant on year-round tourist traffic, were threatened in early 2019 when a massive landslide covered RN 22, Andora’s only roadway connection to France. The indefinite closure resulted in a 3-hour detour through Spain for travelers and the severe damage to the road posed a challenge for local engineers.

The landslide – 328 feet wide, 98 feet high, and 65 feet deep – displaced 654 cubic yards of earth and rock near the bridge of La Mina in France. If the situation wasn't quickly stabilized, as much as 3,924 cubic yards of rock were at risk of falling onto RN 22.

With the town virtually cut off from the outside world and its local economy in jeopardy, the French Departments of Roads for the Southwest (DIRSO) brought in STAM, a civil engineering firm that specializes in difficult-to-access sites in high-altitude, mountain environments. The team of STAM specialists immediately mobilized, deploying five shovel mechanics to work around the clock removing debris from the location at an elevation of 5,905 feet with steep terrain. Once the land was stabilized and the debris removed, the team was challenged with 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 that STAM had worked with previously. Morello then began to coordinate with France’s network of Redi-Rock suppliers, first reaching out to Vincent Lachaux of BBLOX/Lachaux Betons. Lachaux and Morello together obtained exclusive rights for manufacturing Redi-Rock in France in 2016 and have collaborated since then to expand the network to 12 producers under the name ML Rock. 

Three ML Rock producers; AL Rock, BBLOX and Carrieres et travaux de Navarre, all located in southern France, worked together to supply the project. Each manufacturer analyzed their existing inventory of 60-inch (1520-millimeter) blocks in comparison to their forecasted sales in order to ensure they wouldn't jeopardize future projects while also supplying Precast Modular Blocks (PMBs) for the emergency repair.

Redi-Rock’s revolutionary large block retaining wall system was ideal for this complex project, providing a quicker, more structurally sound solution using wetcast concrete with the look of natural stone. Redi-Rock’s one-ton PMBs allowed a greater gravity wall height, eliminating the need to excavate into highway slope for geogrid. This time savings coupled with precast blocks, removed the hassle of using site-cast concrete on such a remote project site. Maintenance crews were able to quickly install the giant interlocking Redi-Rock blocks, which provided critical support for the highway’s shallow sloughs and slides.

In total, AL Rock supplied 200 blocks, BBLOX supplied 130 blocks, and Carrieres et travaux de Navarre supplied 100 blocks. In addition to supplying the blocks on short notice, the quick installation process for Redi-Rock was a huge benefit in this emergency repair as well.

Lauchaux and Morello explained "[there's] no plaster, no joints, no paint, no finish." The blocks leave the factory with a beautiful natural stone appearance ready to be installed.

A retaining wall aided in a landslide repair in Europe.After the base course of the Redi-Rock gravity blocks is set, a typical crew of two to three people and a piece of lifting machinery can set upwards of 700 square feet (65 square meters) a day. In the case of the RN 22 retaining wall, the STAM team finished the entire project – over 2,875 square feet – in just four days.

In total, 33 delivery trucks supplied the 760 tons of Redi-Rock PMBs to craft the wall. The 200 blocks from AL Rock, located in Bort-les-Orgues, France, would travel the farthest distance to the site – 310 miles (500 kilometers). Manufacturers will typically ship Redi-Rock approximately 125 miles (200 kilometers). Despite being two-and-a-half times the standard shipping radius, the PMB solution with Redi-Rock was still a more cost-effective solution than the cast-in-place alternative.

An ideal solution for highway erosion control, the Redi-Rock wall design reduced the incline of the highway back slopes, avoiding future erosion and sloughing. Cast from durable, wet-cast, air-entrained concrete, Redi-Rock products will also perform well against the rigors of Andorra’s freeze-thaw conditions and road deicing chemicals.

The Redi-Rock wall, which curves along the roadway and stretches 262 feet (80 meters) long and 10 feet (3 meters) 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 quick install, the road was quickly reopened and safe for traffic.


About the author