Volume 7, no. 13 - Colbond Geosynthetics

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Will bypass bring mountain idyll back to Giswil? 10 Colbond Geosynthetics News 13 - 2002 Past Oerlikon Stadium, the highway south pops in and out of the shade of a seemingly endless series of cut and cover tunnels, then stretches out along a chain of long lakes mirroring the rocky peaks around. It’s the stuff picture postcards are made of. For the good people of the town of Giswil, Switzerland, however, peace and quiet may only now be returning. For this town of not quite 3,500 souls is located on the main arterial road between the metropolis of Zurich and the city of Interlaken. Convenient enough for the tens of thousands of visitors who come each winter to ski on the surrounding 6,000-foot slopes, but something less than a blessing for the citizens themselves. The beginning of the solution started, however, when the authorities of Obwalden Canton received approval to build a two-kilometer bypass tunnel to lead the N8 national highway around Giswil. The project, estimated at some 121 million Swiss francs, started in 1997 and is scheduled to be open to traffic in the course of 2003. Although the tunnel is not yet open to the public, construction machinery now drives in and out of the south portal, where the first breakthrough came in February of 2000. Inside, the tunnel itself is a model of modern engineering. When completed, the inner shell, with a diameter of a little over ten meters, will house a twolane highway with a maximum speed limit of some 85 kilometers an hour and a gradient of 2.5%. To get there, the builders used more than 50,000 man-hours and 180 tons of explosives to mine their way through sandstone, chalk and limestone formations. Close to the north portal, the almost vertical layers of sedimentary rock produce a flow of a few hundred liters of water per minute in the vicinity of the tunnel entrance.
Today, most of the 2,000 meter gallery has been covered in a 25 - 30 centimeter thick layer of ‘shotcrete’ - liquid concrete sprayed onto the raw rock walls - and a large portion is already equipped with bright orange PVC membrane. Outside the winter sun is bright, but here in the cavern men are working in constant dusk, air-testing the welds on the waterproof liner. “The membrane used in tunnels almost always has a colored signal front layer and usually a black backing,” explains Rudi Kubli of Schoellkopf AG, Colbond Geosynthetics’ Swiss distributor. “That makes it easier to check visually for cuts and punctures.” Behind the PVC at Giswil is some 45,000 square meters of Enkamat ® three-dimensional geospacer, attached to the rock wall at one-meter intervals by means of steel nails and PVC washers. Liner and Enkamat form a ‘sandwich’ when the liner is heat-welded to the washers. Valves located at strategic points in the liner allow air to be pumped behind the PVC to make sure the ‘sandwich’ is truly water-tight. “Tunnels are a major infrastructural investment,” Kubli says. “You can’t afford to close down a tunnel and fix the walls every few years. So the highest safety combined with extremely low maintenance is a very important criterion for specifiers. Colbond Geosynthetics News 13 - 2002 11
Page 1 and 2: Volume 7, no. 13 N GEOSYNTHETICS W
Page 3 and 4: Dear Readers, From the editors Geos
Page 5 and 6: Forces at play Fire safety is a ver
Page 7 and 8: High-pressure cascade Tunnel shells
Page 9: Column “The world changes rapidly
Page 13 and 14: “One way to keep tunnel walls int
Page 15 and 16: Waterproofing system The waterproof
Page 17 and 18: The exceptional conditions of the p
Page 19 and 20: Once the drainage layer and liner a
Page 21 and 22: Present state of development in str
Page 23 and 24: In the case of non-ventilated metal
Page 25 and 26: Reinforced Enkamat Filled Armater E
Page 27 and 28: Mekastone and Enkagrid support Worl

Volume 7, no. 13 - Colbond Geosynthetics

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