At the Sedrun sub-section, two 6.5km long tunnels run through theproject’s most complicated and dif-ficult geological zones. Also in thissection is one of the Gotthard BaseTunnel’s two multifunction stationsthat house crossovers, emergencystop stations, and technical instal-lations for railway operations andventilation. With more than 2000 metres ofoverlying mountain, tunnellingthrough the unstable rock of theTavetsch intermediate massif is par-ticularly demanding work. TheSedrun section is reached from thesurface via a 1-km-long access tun-nel and two independent 800 metredeep parallel vertical shafts. Heavyduty conveying systems supply thetunnelling site with machinery andconstruction materials via shaft II,whilst shaft I is used to bring theexcavated material to the surface.At the foot of these shafts conven-tional blasting and drilling tech-niques are used, rock mass permit-

Downhole Drilling with Compressed AirNEAT construction with Kaeser compressors

ting, to advance tunnelling workboth north and south.

SSppeecciiaalliisseedd ttuunnnneelllliinngg iinn tthheeTTaavveettsscchh iinntteerrmmeeddiiaattee mmaassssiiffSpecialised blasting, drilling andsupport procedures are used in theSedrun section to enable tunnellingto progress through heavily loadedzones in the Tavetsch intermediatemassif. Examples include:

Round-blasting Tunnelling with full-faceheading Additional blasting (to create up

to 70 cm additional space) allowsfor controlled deformation. Thisrequires heading diameters of up to135 m² (normally: 68 m²) Systematic tunnelling face rein-

forcement with long horizontalanchors Initial reinforcement exclusively

with high-deformation capabilitysupport materials (Design: steelmountings with two interlockingrings featuring slide joints, anchors) Application of rigid support ma-

terial (e.g. shotcrete) after deforma-tion has taken place

Systematic use of additional sup-port material (additional anchors,steel arches etc.) backwards fromthe tunnelling face Implementation of further meas-

ures such as grouting and advancedrainageAs deformable steel mountings hadnever been used on this scalebefore, extensive large-scale testsat the construction site itself con-

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AARRGGEE TTrraannssccoo’’ss““bbaassee ccaammpp”” aattSSeeddrruunn

8

The Swiss, who are no strangers to bold engineering schemes, are currently building the ‘Gotthard BaseTunnel’ after 50 years of planning. Forming the main section of the ‘Neue Eisenbahn-Alpen-Transversale’(NEAT) new trans-alpine rail link, the tunnel has become Switzerland’s most ambitious construction projectyet: Miners carry out their work hundreds of metres below towering Alpine peaks and ridges to integrate theSwiss railway system into the European high-speed rail network. Kaeser compressors are also on site toassist with the tunnelling work at one of the most geologically challenging locations.

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Photos: SBB (3)

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Kaeser rotary screw compressorsmounted on tunnel railcars providethe compressed air that powers thedownhole drilling equipment at theSedrun construction site. This sys-tem enables efficient compressedair delivery exactly where it is need-ed, as the air does not have to passthrough long sections of piping.Each compressed air car isequipped with two Kaeser CSDX162 rotary screw compressors anda 3000-litre air receiver per com-pressor. Most of the condensatethat occurs during the compressionprocess is removed via centrifugal

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Author: Klaus Dieter BätzContact: klaus-dieter.baetz@kaeser.com

firmed that the theory worked inpractice. To maximise the narrow workspace,ARGE TRANSCO-Sedrun installed amulti-functional heading installa-tion that is suspended from the tun-nel roof on a monorail system. Inuse for the first time in tunnel con-struction and more usually associ-ated with mining, the four multi-functional machines create a sec-ond work level for the placing ofsteel arches, cutting of anchors atthe tunnelling face and also forapplication of shotcrete at the tun-nelling face.

SSppeecciiaall mmaacchhiinneess,, ssppeecciiaall sseerrvviicceeConstruction machinery supplierAvesco AG, the representative forCaterpillar and Sandvik-Tamrock inLangenthal, was awarded the con-tract to supply ten ‘Tamrock-Axera’drilling jumbos, seven ‘Tamrock-Toro’ front-loaders, four ‘Caterpillar’special excavators, twelve ‘Ram-mer’ hydraulic hammers, as well as‘Sandvik’ drilling steels. Avesco isalso responsible for supervision oftunnelling equipment at the con-

struction site. Avesco Service Tech-nicians are permanently on-site andwork in three shifts, seven days aweek to provide round-the-clocksupport for the machinery. Further-more, a spare parts and a drilling-steel store are located underground,as is an office container equippedwith its own IT infrastructure.

DDrriilllliinngg wwiitthh aaiirr--ppoowweerrA working group of representativesfrom Arge Transco Sedrun, AvescoLangenthal and Tamrock (Finland)developed a special drilling installa-tion that would be able to tunnelthrough the pressure zones of theTavetsch intermediate massif.

Weighing in at over 60 tonnes, thegiant ‘Tamrock Axera T12 Sedrun’can sweep across the entire 13-metre tunnel diameter with itsdrilling arms to set blast holes, self-drilling anchors, as well as casedanchors, up to a drill diameter of140 mm. For cased anchors, themachines use the downhole drillingmethod: Hydraulically driven viapush rods, the rotating drill-bit isequipped with a pneumaticallypowered hammer drill, which with-in this diameter range, significantlyincreases overall system efficiency.Furthermore, it eases the burden onthe hydraulic drive system & borerods, enables precision drilling at

low push rod speeds (10 to 60 rpm)and simplifies setting of linear bore-holes.At the same time, the compressedair used to power the downholedrill-hammer also removes the drilldust from the borehole and addingdust-binding foam to the com-pressed air prevents dust build-up.Downhole drilling is a relatively newprocess suited to large drillingdiameters and has proven particu-larly effective both in extremelyhard and in soft rock masses.

Sedrun Section – Facts and Figures

· Two tunnels approx. 6.5 km long with 50 mseparation

· Connecting galleries every 320 m· Multifunction station with two emergency stops · Total length of tunnelling approx. 20 km· Cost: 1.25 billion CHF· Workforce: up to 450 employees· Installation work: May 2002 to October 2003· Shaft II construction: May 2003 to February

2004· Tunnel blasting begins: July 2003 (North side),

August 2004 (South side)· Estimated breakthrough: Summer 2008 (North

side), Autumn 2008 (South side)· Completion of blasting: End 2008· Concreting and finishing: 2006 to 2009· Handover to owners: Summer 2011

Photo: SBB/AlpTransit Gotthard AG

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TThhee ccoommpprreesssseedd aaiirr ffoorr tthhee ‘‘ddoowwnnhhoolleeddrriilllliinngg’’ pprroocceessss iiss pprroodduucceedd hheerree

separator, whilst ‘Eco Drain’ con-densate drains ensure ecologicallysound disposal. For equipment tooperate reliably and efficiently insuch a hostile working environ-ment, meticulous design and con-struction are essential. Kaeser com-pressors, for example, feature largelow-speed airends filled with gener-ous volumes of cooling / lubricatingfluid to ensure effective removal ofparticles from the intake air. As a result, Kaeser compressorsprovide far superior performanceand reliability compared with unitsequipped with smaller high-speedairends. This advantage is furtherenhanced by Kaeser’s use of amaintenance-free 1:1 direct drivecoupling to turn the airend, as thiseliminates the power losses associ-ated with gear driven systems. With unrivalled quality and depend-ability, Kaeser compressors are intheir element performing such ademanding role at what is one ofthe world’s most challenging con-struction sites.