Twin Robbins TBMs Tackle Dahuofang Water Transfer TunnelsConstruction of the 85.3 km-long Dahuofang water transfer tunnel is expected to be completed at the end of 2008. The central area of Liaoning Province, northeast China, will receive an additional 1.8 billion cubic metres of water annually for local people and for agricultural and industrial production. The tunnel and diversion pipelines with a total length of 231 km will bring water from the Dahuofang Reservoir in the east of Liaoning to 10 million people in six industrial cities in the province's central region. The region is short of water, with per capita water resources less than 700 cubic metres. According to international standards, regions with per capita water resources of less than 2,000 cubic metres are taken as places with serious water shortage. 40% of tunnel is being excavated by drill and blast, while the remaining 60% is TBM-driven. TBM 1, one of two Robbins main beam TBMs on the job, broke through into an intermediate adit on 21st December, 2006. The breakthrough follows that of TBM 3, which reached its intermediate adit in September 2006. The TBM-driven portions of tunnel are divided into three contracts. Both contracts for TBM 1 and TBM 3 are using 8.03 m-diameter Robbins TBMs, conveyors and backup systems, while the contract for TBM 2 chose a collaboration of companies for the TBM, backup, and conveyor system. Both TBMs 1 and 3 have been boring since August 2005 on very long bores of 17 km and 13.6 km, respectively. TBM 1, after boring 10.4 km, will stop for a 2-3 month maintenance programme before continuing on the final 6.6 km leg of the tunnel. The tunnel and adit conveyors, tunnel utilities, and main transformers will be relocated to the new tunnelling site at the intermediate adit.The geology for the first section of the TBM 1 contract consists mainly of migmatite, andesite, syenite and compound granites with UCS values up to 109 MPa. The TBM 3 contract involves variable rock types, often in mixed face combination, of andesite, tufaceous brecciated lava, volcanic breccia, tuff, and tufaceous siltstone mixed with shale, sandstone, and mudstone. The rock strengths range from 19 to 30 MPa. Though the types of rock vary widely, both TBMs 1 and 3 are performing extremely well after 17 and 14 months of boring, respectively. As of mid-December 2006, data show that TBM 1 had bored 10,438 metres and had achieved a monthly average of 614 metres. TBM 3 also clocked in very well at 508 metres per month. The progress of TBM 1 is all the more remarkable considering it has surpassed TBM 2 in metres bored, even though it began seven months later. As of December 2006, TBM 2 had bored 10,133 metres in 24 months, more than 300 metres behind TBM 1, and was averaging 440 metres per month. Click here.TBMs 1 and 3 are utilizing several technologies that may be contributing to their fast advance rates. Both are using 48 cm back loading cutters with front loading optional, rather than 43 cm cutters (the size being used on the TBM 2 contract). Larger cutter diameters increase cutter life and cutter load capacity, allowing the TBM to bore faster in harder rock. In addition, TBMs 1 and 3 are using conveyor systems supplied by Robbins. The project is the first in China to use continuous conveyors for tunnel excavation. Steel cable belt is being used, rather than fabric belt, in order to accommodate the extremely long and straight tunnel paths. Steel cable has a higher strength than fabric, which allows the use of much more powerful conveyor drives. The 900 kW drive motors are three times more powerful than typical drive motors and reduce the need for booster drives in the tunnel. In fact, both contracts for TBM 1 and 3 are using only one booster drive despite the tunnel lengths.When boring is complete, the Dahuofang water transfer project will be one of the most extensive water transfer projects in the world. The tunnel will transfer water from the Huanren Manchu autonomous county to the Dahuofang reservoir in Xinbin Manchu autonomous county to supplement the arid and densely populated Shenyang region of China. Read E-News Weekly 40/2006. Click here. Visit www.therobbinscompany.com 07/07.