Tunnelbuilder Promoting the world's tunnelling industry to a huge qualified audience

View the Spanish Tunnelbuilder website View the Italian Tunnelbuilder website

Challenging Casing System and Blast Monitoring at the Saas Tunnel in Switzerland

Challenging Casing System and Blast Monitoring at the Saas Tunnel in SwitzerlandThe valley of Klosters and Davos, worldwide known from the annual World Economic Forum, provides a crucial passage in the Canton of Grisons in the East of Switzerland. However, besides the regular commuters, the traffic added during the winter season increases the load above the acceptable level in the area, especially in historic towns with narrow roads. In order to reduce this load and eliminate the traffic problem on road A28 from Landquart to Davos, major investments are made for bypassing Klosters with the Gotschna tunnel, already opened (read E-News Weekly 1/2006), Küblis and now Saas. The key structure on the Saas road bypass is a 2,577 m-long bidirectional tunnel beneath Saas, including open cut stretches of 130 m at the junction of Saas West and 15 metres at the Waldhof portal. The tunnel begins at the Saas portal in the west and climbs a 2.6% gradient heading east to Waldhof. The smallest radius is 600 m. The transversal slope is 6.5% in the curves and 3% in the straight lines. Its cross-section ranges from 83 to 90 square metres, according to the primary support. A 2,320 m-long 17 sq m rescue tunnel is built at 30 metres parallel to the main tunnel and the two bores will be cross-connected by eight passages every 300 metres approximately. Three lay-bys will be spread out through the main tunnel. LED indicators along the pavements and on the middle line will materialize the roadway to increase security. Emergency call niches and fire extinguishers will be placed every 150 metres. The ventilation system will supply fresh air via a ventilation duct and remove smoke via a parallel duct above the concrete ceiling. Moreover, the tunnel will be monitored by video cameras and have mobile phone reception. Sensors will permanently measure the wind in the tunnel, visibility and CO2. Read E-News Weekly 31/2002.The owner is the Canton of Grisons. The project designers are Pöyry and Amberg Engineering. Toscano is the project manager. Visit www.tiefbauamt.gr.ch/projekte/index.htm, www.poyry.com, www.amberg.ch and www.toscano.chATUS (ATUS Arbeitsgemeinschaft Tunnel Umfahrung Saas), a joint venture consisting of Walo Bertschinger, CSC, Rothpletz, Lienhardt + Cie, and Gebr. Vetsch, was awarded a CHF130 million contract for the tunnel. Work commenced in 2002 and the tunnel is scheduled to open to traffic on 11th November, 2011. Visit www.walo.ch/deutsch/projekte/aktuelle-projekte/untertagebau/umfahrung-saas.htmlAbout 80% of the length (approximately 2,000 metres) is shale with incrustations of calcite and very thin layers of the so-called kakirite, cataclastic fault rocks. The remaining 20% (approx. 500 metres) is soft ground with erratic boulders of 1 to 10 cubic metres.The main tunnel is bored in rock from the west by drilling and blasting in a top heading and bench sequence, using liquid explosives supplied by Explotec. A Tamrock three-boom Axera T11 drill rig is used. After blasting and mucking-out, the spalling of rock is eliminated by an Eickhoff ET 30 rotary head mounted on a Liebherr 932 excavator. To date, there is still 50% to bore. Breakthrough is planned where the hard rock meets the soft ground. Visit www.explotec.ch, www.eickhoff-bochum.de and www.liebherr.comSupport is made of a first layer of shotcrete (7 cm, CEM I 42.5 cement) reinforced with Bekaert ZP 35-65 steel fibres (35 kg/cu m) sprayed by a Meyco Potenza shotcreting pump, 4 m-long Belloli steel anchors with chemical cartridges, welded mesh (K188) and a second layer of shotcrete of 15 cm. Visit www.bekaert.com, www.meyco-equipment.ch and www.belloli-italia.it/belloli/inglese/index_inglese.htmThe emergency tunnel has been excavated through rock by a 4.5 m-diameter Jarva MK12 TBM. The machine completed its work in November 2006. Support is identical to that of the main tunnel. The mucking-out system was supplied by Rowa Tunnelling Logistics. Visit www.rowa-ag.ch/images/PDFs/ref_UmfahrungSaas_d.pdfNot only the ground conditions encountered at the Saas tunnel by crews make it a very challenging drilling case in the soft ground but also a premiere in Switzerland to monitor the blasting with a dynamic system. Robit forepoling of steel piles drilled into the soft ground Blasting monitoringDue to the geological conditions the tunnel is excavated using blasting technology. Since blasting induces vibrations that could lead to damages to some buildings located just above the tunnel, the project owner, the Canton of Grisons, decided to install a dense monitoring system for the control of seven buildings. The system is designed to provide the means to understand, avoid and determine early potential risks associated with the high vibration impact on specific structures due to blasting within the overall project quality management.GeoSIG was selected to install and operate the dynamic monitoring system supervising the blasting work performed during the construction of the Saas tunnel. The monitoring system utilises a VE-33 velocity sensor installed at the basement of every building to be monitored. All the seven sensors are connected through a cable to a CR-5 central monitoring system. This is the first installation in Switzerland of a dynamic online monitoring system based on the internet as data communication media. Visit www.geosig.comCasing system in soft groundThe main tunnel in soft ground (500 metres) requires the drilling of pipe roof umbrellas due to difficult geological conditions. The descending excavation from the east is performed under umbrellas of steel pipes on a total length of 500 metres, starting from the newly built Hexentobel bridge. The pipe roof umbrellas are drilled using a casing system supplied by Robit Rocktools. The ground conditions consist of an alternation of hard weathered rock and soft ground. Most of the tools available for forepoling applications cannot be used in this type of condition due to the high drilling requirement. When most of the forepoling products are made to be used in relatively soft ground, the robust Robit casing system, also called RoX, was designed to be used from the softest conditions to the toughest rock. Visit www.robit.fi. Bolting with Tamrock jumbo The ATUS JV has chosen Robit among several suppliers for the supply of the casing system to drill all of the pipe roof umbrellas. The roof reinforcement consists of 30 arches of 30 piles. Each pile will be a 14 m-long casing, with pipes of a diameter of 114.3 mm and a thickness of 6.3 mm. The equipment to drill the pipe roofs is a Tamrock Axera T08 two-boom jumbo and Sandvik rods. The ATUS JV has contracted Ceresola TLS to supply the tubes produced by Mec Edil of Italy, for whom they are distributor for the project. Visit www.miningandconstruction.sandvik.com, www.ceresola.com and www.mecedil.comThe RoX is a ring bit system composed by two parts: a pilot bit and a ring bit on which a casing shoe is mounted at Robit's factory. The easy automatic connection between the pilot bit and the ring bit leads to a quick learning process for a first time use and to a fast drilling for the experienced RoX users. Further to cement grouting in the 30 piles with a Häny pump, excavation is performed metre after metre using a Liebherr 934 excavator prior to the placement of Jorimann HEB 200 or HEA 280 steel arches in three steps (top heading, benches and invert). Concrete is poured in the space between the steel arches by a Meyco Potenza pump. Visit www.haeny.com 15/07.