Tunnel Business Magazine

JUN 2018

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Page 17 of 51

in geology for which it's suitable," said independent consultant Joe Roby, who has decades of industry experience. "I'd argue that history shows the reverse— ra erforming better than used — a used machine is a proven design and more likely to have a successful future." Large metro projects worldwide often ulta- neously, resulting in a glut of secondhand machines on the marketplace at any given time. But contractual constraints often form barriers toward using these ma- chines on subsequent projects. "Consul- tants employed by project owners often over-specify technical specs — I've also seen a lot of cases where they are doing a cut-and-paste job on the specifications without checking on the requirements. Sometimes the consultants don't have the erience, and it shows in the speci- fications," said Roby. He added, "I think it's important to continue education — the risks of over- specification may cost contractors and owners in the end. I think what owners ought to be doing, rather than over-speci- fying or specifying new machines only, is to specify the quality of the rebuild that is necessary. But that requires a certain lev dge from the consul- tants. Certain things could be specified, like that the main bearing is new or has to be certified for a certain number of hours. A cutter load could be specified for hard rock tunneling, but details like thrust and torque should not be specified." F unnel- ing and Civil at iPS who has rebuilt ma- chines worldwide, the bias toward new machines is readily apparent. "For ex- ample, over-specification was initially quite prevalent in Singapore. There was no reuse of machines allowed on the early round of metro projects. At one time, there were eight used machines sitting in a storage yard of identical size to what was specified but we couldn't use them." However, over time a more enlight- ened view did develop to allow reuse of y machine proposed for reuse had to leave Singapore for refur- bishment in the original manufacturer's facilities. Willis continued that on some projects, such as India um o, initially there was a similar philosophy but a stipulation was later added to allow refurbished machines to help meet the aggressive delivery schedule. A Record of Success So is newer really better? In many cases the record shows that they are equivalent. Changing opinions about rebuilt machines can be done, says Roby: "We have to show evidence where refurbished machines have been used, and show their track re- cord. If you can show that performance and price were good on a given project that is important. Time should also be considered: A refurbished machine can be important if you're looking to get started quickly. It can save a lot of lead time." If the age and number of projects bored een by some as an issue, a history of record-breaking projects achieved using rebuilt machines does ex- e than one third (36%) of currently standing world records have been broken using a refurbishe ome of them in service for decades. Rec manufactured in 1980 achieved three world records in the 6 to 7 m diameter range at the Deep Rock Tunnel Connec- tor (DRTC) in Indianapolis, Indiana. The 6.2-m diameter Beam had pre- viously bored at least five other hard rock c- ond Avenue Subway. Design updates for the DRTC included a new back-loading cutterhead with 19-in. disc cutters, vari- able frequency drive (VFD) motors, and a rescue chamber. The records included e d in One Day" (409.8 e d in One We eet " (5,754.6 ft/1,754 m). The machine is currently boring the next phases of the DigIndy network—a further 28 km in addition to the 12.5 km DRTC already completed. In cases where it is believed that new erform better, there is likely an experience bias at work, says Roby: "I would expect people might have experi- ence of one such job where that was true, and it's dominating their thoughts. y experience over the years has been that there are a lot of successful secondhand es are rare and gener- ally only happen in extreme conditions. A failed project can oftentimes be the re- ed where it wasn't suitable or wasn't rebuilt properly." He added that, if an older machine was "ini- tially built for sandstone, it will not have enough power to work well in granite 25 years later without modifications." A custom design, for a project's specific requirements and geology, is just as impor- tant on a rebuilt machine as a new one. For example, a contractor may wish to save money by purchasing a use rebuilding it to its original specifications. ebuilt to the same diameter and specifications, will cost less than rebuilding the same machine but increasing the size to 4 m and adding custom elements. But are the savings truly obtaine specifications do not fit the geology? Cut- terhead configurations are a particularly important example, with cutter spacing, cutting tools, cutterhead geometry, and muck openings all coming into play and greatly affecting the rate of penetration. A good example of this concept can be seen at o City's Túnel Emisor Ori- ente (TEO). The geology is highly variable, with the tunnel 62 km in length and up to 150 m deep. One 8.93-m EPB was used to bore two separate lots with very different geology: Lot 1 and Lot 5. At Lot 1, the machine was used with its original cutterhead and soft ground cut- ting tools, along with a two-stage screw conveyor, to excavate watery lake clays with great success. The machine bored 4.6 km to complete its section of tunnel on the critical path. The cutterhead was designed as adaptable for both hard rock and soft ground configurations, but before it began excavation of the 8.6 km long Lot 5, it needed some modifications. Person- nel added grizzly bars across the muck openings as well as heavy duty abrasion- resistant wear plating. Wear plating was also added to the screw conveyors so they could be used in open mode during ex- cavation in rock. Lot 5 is one of the most TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // JUNE 2018 C O V E R S T O RY 1 8

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