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Blasting Works, Public and Specialized Works

RD 52 – Réouverture de la route


The local people in the towns of Brenon, Châteauvieux, La Martre are smiling again. After being closed to traffic for one year, departmental road 52 is expected to reopen early in June at the latest.
Reinforcement works were launched in late March and the team from "Minages et Travaux Publics Spécialisés" (MTPS) at Noailhac (Tarn) has been working on it late into the evening.
"Feuille de Chou" was given the opportunity to enjoy a guided visit of the site under the supervision of site foreman Gilles Arnaud. The affected area is a 45-m long and up to 8-m deep straight stretch of road, which is to be, so to speak, 'swaddled'.
Several phases took pace. The first phase consisted in driling in micropiles to a depth of 20 m (to ensure proper anchorage). A 25-ton excavator-mounted hydraulic drill was used. The technique involved drilling holes 25 cm in diameter, in which metal micropiles 14 cm in diameter were inserted and sealed with micro-concrete injections.
The 'nailed wall'.
During our visit, André gave us an overview of the work to come. "Once the micropiles have been installed," he said, "we shall enter the so-called excavation phase, and then the wall-nailing phase. This is a time-tested technique devised to neutralize the risks of landslide.
There are 50 nails of about 16 m each, which require horizontal drilling as well as drillling perpendicular with the micropiles. The engineer added that the 50 nails will need to be distributed along 4 rows down to the bottom of the wall (8 m for the last level).
The 'welded mesh' procedure plus two coats of projected concrete will be applied to secure them in place.
Once this is completed the wall will be "nailed" and the reinforcement phase will end. A coat of concrete will put the finishing touch before the work is officially launched. Giles Arnaud, whom we interviewed, confirmed that the ground where the collapse occurred is made of viscous loam, a sedimentary compound composed of nearly equal parts of chalk and clay, and geologically unstable.








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