New life for Canadian mine - Atlas Copco

Reinforcing the Torrebaso tunnel: So far, five pipe roofing umbrellas have been installed providing quick and effective support ahead of the excavation.Eight more umbrellas are planned, 9 m in length, to support a further 50 m of the tunnel.The Symmetrix solution has been successfullyused in similar ground conditionsaround the world and in Spain it is one ofGeotunnel’s specialities.Borja Del Palacio of Geotunnel, says:“We have installed hundreds of meters ofpipe roofing around the country and I haveto say Symmetrix is my favorite method.“It is fast, reliable and economical andthe quality of the bits and tubes we getfrom Atlas Copco is very good. Also, aswe can use the same rig for pipe roofingas for drill and blast, it is not necessary tosub-contract this work to a specialized piperoofing company.”Andoni Bonaechea, Technical Office andPurchasing Manager, who decided to adoptthe method at this site, is especially pleasedwith the way the work has progressed. Hesays: “Pipe roofing using the Symmetrixsystem is by far the fastest and most economicalway of stabilizing unfavourablerock conditions in tunneling and we haveproved it at Torrebaso.”It is estimated that more than 5 200 m 3 ofrock and soil will be excavated here and thatthe necessary stabilization and reinforcementwork will require the installation of 1 824 mof steel pipes and 35 000 kg of cement.For pre-support before each advance, theBoomer has installed five umbrellas with anaverage of 30 pipes per umbrella, each 12 mlong. A starter pipe fitted with the standardSymmetrix ring bit set is used followed byextension pipes – in this case, 89 mm pipeswith a 7.1 mm wall thickness using theSymmetrix P89 system.Fast installationThe pipes are installed at an angle of 4°and spaced 30–50 cm apart. Once installed,they are grouted in place to form a strongumbrella or canopy around the upper partof the tunnel profile.Net drilling time for a 12 m pipe averaged10 minutes and the total time forinstallation was 30–40 minutes per pipe,depending on the condition of the rock andother operational factors. As a rule, eachinstallation was perfectly straight.Alas Copco’s Area Manager Jorge Diazsays: “Geotunnel has long experience ofSymmetrix-based pipe roofing and thecompany chooses to work with us becauseof the features and quality of the Symmetrixsystem and the service that we provide.”Sole supplierIn addition to Spain, pipe roofing using theSymmetrix system has been successfullycarried out in many other countries includingPortugal, France, Sweden, Kazakhstan,India and the Czech Republic.Furthermore, Atlas Copco is currentlythe only supplier in the world to offer acomplete package of equipment for thistechnology – Boomer drill rigs, SymmetrixCasing Advancement System together withpipes, Secoroc drill rods and Unigroutgrouting equipment. (See facing page).Footnote:At the Torrebaso tunnel project, Geotunnel operatesas a subcontractor within the consortium CorsanCorviam/Balzola. The client is Ute Euba-Iurreta andthe project has been commissioned by E.T.S. (EuskalTrenbide Sarea), the housing, transport and publicworks authority of the Basque administration.Dealing with difficult groundThe Symmetrix Casing Advancement System is based onthe rotary-percussion drilling method and consists of apilot bit and a ring bit.The pilot bit is attached to the ring bit with a bayonetlocking mechanism. Together they drill the hole which islarge enough to allow the casing to advance simultaneouslyas the hole is being drilled in loose and collapsingground conditions. During drilling, the pipe itself does notrotate so there is no need for high torque on the drill rig.A special feature of the system is that flushing is carriedout through the annulus between the casing pipe anddrill pipe, ensuring high efficiency with minimal damage to theadjacen t formation.When the hole is complete, the pilot bit is unlocked from thering bit and withdrawn through the casing pipe together withthe drill pipe. The casing pipe (and ring bit) can be permanentlyleft in the ground or retrieved from the hole.Symmetrix is designed for installing casings with a diameterof 76.2 to 1 220 mm (3–48 inches). It offers a highly efficientmethod with great productivity and is used worldwide for avariety of applications in, for example, tunneling, foundationdrilling and well drilling.20 Mining & Construction – 3 / 2011