Following the development of the reverse-circulation drilling technique in Japan, trench-cutting machines took off in Europe, according to USSD. In 1984, German contractor Bauer A.G., Schrobenhausen, used one of the first trench cutters to build a 40-m-deep wall in sandstone at the country's Brombach reservoir. In 2006, the company claimed to have reached a 116 m depth for a cutoff wall at the Perimbonka hydro dam, Quebec, Canada.
In the mid-1980s, before being acquired by Trevi, the contractor Rodio S.p.A. used a milling machine to drill a 100-m-deep wall in sandy, gravely soil for a demonstration trial near Milan. Early this summer, Rodio claimed another, deeper success, testing Soilmec's S-135 rig down to 150 m.
But Trevi has yet to go anywhere near that deep on a commercial contract. In an equal partnership with Paris-based Soletanche Bachy S.A., the group's biggest-ever contract for a cutoff wall is now well advanced on the Wolf Creek Dam foundation remediation project in Russell County, Ky. The contract, signed in 2008 with the Army Corps of Engineers for $341.4 million, calls for a 1.2-km-long, up to 84-m-deep cutoff wall, including slurry walls and secant piles (">ENR 2/27/12).
While the big leap in wall depths excites Trevi engineers, its reception by dam designers likely will be restrained. "There is no doubt that what they are suggesting is new," says Tim Hill, the Cambridge, U.K.-based head of hydraulic structures at the design firm Mott MacDonald. But the technology's newness "tests the way the dam industry works, because we are very conservative," he notes.
Hill acknowledges the scarcity of alternatives to concrete walls for plugging leaks in soluble rock-dam foundations. "People have tried grouting, but that has had very limited success," he says. "I am excited that it's new, but somebody has to stick their toes in the water first."
While there is demand for deeper walls, Siepi agrees that, "at the moment, there are few projects where the capability of this rig will be required." He adds, "There are serious projects to build something like that, although at this time I cannot disclose where [those projects are]."