SUSTAINABLE TUNNELING | TECHNICAL


“As long as it is well-maintained there will be jobs


that it can bore economically.” The limitations that do exist are primarily to do with


the original quality of the machine. “Overall, the life of a TBM is a function of the


fundamental design. If it is intended for a hard rock tunnel it will be designed from the outset to be robust, with greater strength of core structure and final drive components.” He says that Robbins High Performance (HP) TBMs


are an example. Quality assurance should mean that a design life of 10,000 hours is perfectly reasonable. “A machine that is designed for multiple projects will


have a robust cutterhead and a heavy steel structure and will take into account the effect of highly abrasive excavated material.” Regular cutter inspections, he adds, should be


designed into the cutterhead. Crucial components are the main bearings and seals. “Bearings and ring gear are difficult to access, so they


must be designed for longevity from the outset. Large- diameter three-axis main bearings need the largest possible ratio of bearing to tunnel diameter – that gives them the dynamic capacity to withstand more load impacts and, therefore, have longer life.” Hardened wear bands are essential, he says. “Many other manufacturers do not use wear bands,


so as the TBM operates it wears a groove into the seal lip contact zone.” Gear boxes, on the other hand, are less critical: if


the TBM has bored more kilometers than they were designed for, replacement can be planned without too much difficulty. Having obtained a good-quality TBM, maintaining it is


important: regular inspections and checks – of cutters, of fluid levels and the like – should be part of a daily monitoring log, he says. Given this careful treatment, a quality TBM can be


rebuilt cost-effectively project after project, he adds. In fact, several known, active TBMs are still boring tunnels after more than five decades of use and 50km of total tunneling.


CASE STUDY: TBM ON DIGINDY, INDIANA What is an example of how this TBM re-use works in practice – for a contractor? The webinar offered, as an example, the DigIndy


Project in Indianapolis, Indiana, US for consideration. There, contractor J.F. Shea is using a rebuilt TBM to great effect. The 20.3ft (6.2m) diameter Main Beam TBM on the project was originally built to bore New York’s East 63rd Street subway – back in 1980. A tunneler starting with it as a brand-new machine


at the beginning of his career will now have retired. The TBM, however, has not retired. Since it was manufactured, the TBM has bored at least five hard-rock tunnels, spent some time tunneling in the UK and, back in the US, the machine recently finished boring more than 25 miles (40km) of tunnels below Indianapolis.


During the course of the DigIndy project, the TBM set


three world records in its size class (6m-7m diameter), including a best 24 hours 136.6yd (124.9m), per week 563.3yd (515.1m), and per month 1918yd (1754m). Over the course of that half-century of work, the


machine has been rebuilt multiple times, notably in 2012 when Robbins refurbished the cutterhead, the variable- frequency drive (VFD) motors, and the rescue chamber. It has 19” cutters, increased from the original 17” ones. The TBM has 2,088kW of power delivering 2,237kNm torque, and weighs 417 tonnes. Christian Heinz is the J.F. Shea’s project manager for


the Indiana project, which is known as DigIndy. A used TBM is nothing new for him. He says that, in fact, he has never yet in his career worked with a new machine. DigIndy is an EPA-funded project intended to clean up


the city’s present system of combined sewer overflows (CSO) which empty into the White River. The tunnels are 76m below ground where the geology is of moderate to very strong rock, generally low to abrasiveness but 31% was tested at medium abrasiveness, the strata comprising limestone, shale and dolomite. It has been a 10-year project. Tunnels bored by the Main Beam include the DRTC,


White River, Lower Pogues Run, Fall Creek and Pleasant Run. On DigIndy, the networks of tunnels bored by the TBM totals more than 45km. Having competed its role in DigIndy, the TBM’s


cutterhead has been removed and the whole machine is being put into storage until needed next. “The machine was stoutly built to start with, so it


could cope with the changes that were made to it,” says Heinz. “If there is anything that we can do in our industry to help the environment, we should be doing it. Around half the tunneling jobs in the US are to some degree connected with improving sewage flow; their whole purpose is to clean up the waterways of the US. Any ways that we can help with that are beneficial.” With which Harding agrees: “Most tunneling projects


are environmental somehow. What it all adds up to is that we shouldn’t re-use a TBM just because we happen to have it. That is a mis-application. Tunneling is complex, and you may well need a custom machine for a custom project. But the more geological information we have about a project the more likely it is that we can refurbish a TBM to serve that project. “We are seeking to fulfil a commitment; and as


engineers we need to supply good solutions that benefit the environment. If we can make an impact on that, so much the better.” Meanwhile game fish have already returned to the


White River as a direct result of the DigIndy project; which would seem to show that the environmental value of the tunneling effort, and of the re-furbished TBM, is a real one.


The Robbins/Tunnels and Tunnelling International webinar ‘Sustainable Tunnelling: how rebuilt TBMs can reduce environmental impact and make your project a success’ is available free to view on demand at https://bit.ly/3FxsESZ


Summer 2023 | 17


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