Tunnel Business Magazine

JUN 2018

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TUNNELINGONLINE.COM B U S I N E S S B R I E F S 6 TBM: TUNNEL BUSINESS MAGAZINE // JUNE 2018 Contractor Eiffage Civil Engineering is operating the machine, which launched in 2017 for the Galerie des Janots project in La Ciotat, France. The cavern, studded with stalactites and stalagmites and mea- suring 8,000 cubic meters (283,000 cubic ft) in size, was grazed on the tunneling operation's left side. The crew named the cavern "gr esimple" after their site geologist. "We hit the corner of it. To cross it, we had to erect a 4-m (13-ft) high wall of con- crete s ve something to grip against," explaine c Dhiersat, Project Director of Galerie des Janots for Eiffage. A small door allowed access in- side the cavity, which formed naturally at a point 60 m (200 ft) below the surface. d up and was able to successfully navigate out of the cavern in eight strokes without significant down- time to the operation. "This is certainly unusual, to come across a cavern of this size and signifi- cance. It is somewhat related to the geol- ogy, with karstic and volcanic formations having the most potential for under- ground cavities," said Detlef Jordan, Rob- ope. Karst cavities were a known risk during the bore, but the cavern was not shown in vertical borehole reports conducted from the sur- face along the alignment. A further 1.8 km (1.1 mi) will need to be tunneled before the 2.8 km (1.7 mi) tunnel is complete. "It is possible there could be more unknown caverns. We have a geo- te stem on the machine, and are conducting probe drilling, shot- creting, and maintenance in a separate shift," said Dhiersa stem, standing for Bore-tunneling Electrical ound predic- tion technique using focused electricity- induced polarization to detect anomalies The crew encountered difficult ground conditions early on in the bore, consist- ing of limestone with powdery clays. "When the machine is boring it does well. We have good production and it's a good machine for hard rock. But sometimes it's not hard rock that we encounter," said Dhiersat. The weak rock and clay conditions necessitated ground support including resin-anchored bolts and rings in bad ground, topped with a 10 to 15 cm (4 to 6 in.) thick layer of shotcrete. Despite five months of poor ground conditions, Eiffage is optimistic that conditions will improve and the tunnel will be complete in the next four to five months. Galerie des Janots is one of the 14 oper- ations designed to save water and protect resources, which are being carried out by eille-Provence metropolis, the wa diterranean Corsica, and the State Government. The future Janots gallery will replace existing pipelines currently located in a railway tunnel—these original pipes have signifi- cant deficiencies with estimated water losses of 500,000 cubic meters (132 mil- lion gallons) per year. The completed tunnel will pass under Le Par tional des Calanques, with cover between 15 and 180 m (50 to 600 ft), in order to replace the pipes that are currently being utilized for the water supply networks. "The current pipes have a capacity of transit limited to 330 liters (87 gallons) per second, which is largely insufficient in the summer period. The objective of the operation is to secure the lines and increase capacity to 440 liters (116 gallons) per second," said Dhiersat. Robbins TBM Uncovers Spectacular Cavern at Galerie des Janots The Robbins TBM encountered an unexpected cavern measuring 8,000 cubic meters (283,000 cubic ft) in size. The 3.5 m (11.5 ft) Robbins Main Beam TBM is boring a 2.8 km (1.7 mi) long tunnel for the Galerie des Janots project in La Ciotat, France.

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