The community of Saint-Jean-Cap-Ferrat between Nice and Monaco extended the 50-year-old sewage system. The entry point of the HDD operation (Sea Outfall) was located at the "Pointe de la Causinière", which was situated directly next to a narrow coastal road at the foot of a hill topped with luxury mansions. The access routes are narrow and winding, the space on the jobsite is very tight. The seafloor is covered with corals. So, for environmental reasons, the muck could not be removed with bentonite.
The jobsite team employed a Herrenknecht HDD Rig HK150C. Navigating the mobile Crawler Rig to the jobsite was a precision job before it was brought in pilot-bore position to build the pipeline from ashore into the sea. The planned pipeline alignment demanded a steep entry angle of 22 degrees. This was handled by the Herrenknecht rig and the specially adapted jobsite installation without problems. The muck was removed with compressed air from a compressor installed on the jobsite.
The geology was a real challenge for the tunnelling technology: intially brittle and poros fold rock made up of clay and limestone, followed by weathered rock and sandstone formations. The first ten tunnel meters were lined with concrete to avoid a collapse of the borehole and to make the muck removal by comressed air more effective. After the pilot bore, the expansion of the drill hole and the installation of the product pipe, the construction works were completed on July 4, 2007.