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  • Type: Dam
  • Location: Carcassonne, France
  • Area: 25,000 m²
  • Product: NTP3

The La Galaube dam is the final component of the Montagne Noire water management system above Carcassonne. This system, which already includes the Saint Ferréol, Lampy and Cammazes dams, constitutes a reserve of more than 35 million cubic metres intended to supply drinking and irrigation water to three departments: Aude, Haute-Garonne and Tarn, and to regulate the Canal du Midi.

It is a rockfill dam with impermeable upstream facing. The facing’s waterproofing component consists of 10 cm of 0/20 gravel impregnated with bitumen emulsion, 10 cm of 0/10 cold bituminous concrete, a COLETANCHE® NTP3 bituminous geomembrane and 10 cm of fibre-reinforced concrete laid on a geotextile.

The COLETANCHE® NTP 3 bituminous geomembrane was prefabricated in 5.15 metre wide rolls. They were manufactured according to a precise pattern in order to fit the site without requiring seam welds. Some of the rolls were over 100 m long and weighed over 3 tonnes.

They were unrolled using a horizontal beam carried and controlled by a specially adapted hydraulic excavator An overlap of 20 cm was used when unrolling the strips to allow for welding.

The high surface mass of the bituminous geomembrane limited wind uplift and creases, making it easy to weld with a gas torch and then carefully roller-press. To prevent the geomembrane from slipping, it was anchored to the dam crest by iron staples and covered with unsorted material.

At the foot of the face and all around the perimeter, the bituminous geomembrane was attached to a reinforced concrete plinth anchored in the rock. This plinth provides continuity between the waterproofing of the face and the foundation. The geomembrane is attached by torch welding with a bituminous primer, reinforced by stainless steel components bolted into the plinth. A strip of approximately 1 metre of COLETANCHE was then welded across the components.

A protective mechanical layer was essential to ensure that the geomembrane could withstand all kinds of damage (ice jams, vandalism, etc.). This protection is provided by concrete slabs poured in place on an anti-puncture layer consisting of a heavy-duty non-woven geotextile.

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