Robbins TBM Goes on the Fast Track for Papua New Guinea TunnelA 5.6 m-diameter high performance main beam TBM will be delivered on a "fast track" programme just six months after contract signing. The Robbins TBM will be used for a series of dewatering tunnels at the Ok Tedi mine in Papua New Guinea, with excavation beginning in the first quarter of 2008. With the expedited programme, required by the mine, it was necessary to utilize a re-manufactured TBM. Previously, the machine bored the Little Calumet leg of the Tunnel and Reservoir Plan (TARP) in Chicago, Illinois, earning a world record for boring 2,163 m in one month. Robbins will supply the TBM, back-up system, 48.3 cm cutters, and spares for the Ok Tedi tunnels, as well as field service personnel for TBM assembly and commissioning onsite. In total, three dewatering tunnels will be excavated at the mine, measuring 4.2 km, 900 m and 1.2 km in length. All three tunnels are located in complex geology consisting of siltstone, intrusive porphyry, and limestone with possible fault zones and karstic structures. Rock strengths of up to 285 MPa UCS are expected, though the average is estimated to be 100 MPa. Geological conditions will be verified using a probe drill capable of extending anywhere from 30 m to 100 m ahead. The results will be used to determine if any aquifers lie ahead in the bore path. Two roof drills will be used for tunnel support and are capable of installing 2.4 m-long bolts in unstable areas. An invert thrust system will be used as the machine bores through fault zones. The machine will push off of the concrete invert to reduce the required gripper force against the tunnel walls. The Ok Tedi mine is currently one of the world's largest suppliers of copper, but its open pit reserves are forecast to run out by 2013. Rainfall at the site averages about 10 m per year, necessitating additional drainage from the open pit beginning in 2009. Once complete, the new dewatering tunnels will extend the life of the mine by providing a high volume of drainage underneath the active mining application. In the future, the tunnels may also be used to identify further deposits of gold or copper. Visit www.therobbinscompany.com and www.oktedi.com 04/08.