TECHNICAL | SUSTAINABLE TUNNELING
USING REBUILT TBMS TO HELP REDUCE ENVIRONMENTAL IMPACT
The world needs to reduce its carbon emissions. The tunneling industry needs to play its part in that effort. TBM makers Robbins recently came together with TTNA to host a webinar on how re-using TBMs can help reduce the carbon footprint of tunnel construction. Doug Harding, vice-president of Robbins, and Christian Heinz, project manager for J. F. Shea, gave the benefit of their experience and answered questions from participants. Julian Champkin moderated the discussion and reports on the webinar
A tunnel in use is generally a carbon-saving device. Whether it shortens a transport route thus reducing emissions, or provides a rapid rail link over a road alternative, or eliminates a ferry crossing over a water barrier, the end result is likely to be fewer carbon emissions. There are other environmental benefits as well. Bored tunnels have less impact at the surface than
other construction options, such as bridges, cut and cover tunnels, and surface roads and railways. This is particularly true for sensitive environments or urban areas that lack available space; tunnels keep such impacts to a minimum.
The actual construction of a tunnel, though, is a
different matter. It is a hugely energy-intensive affair, both in the physical extraction of the rock or soil and in the embodied energy of steel and, in particular, of concrete. For tunnel construction in general, consultancy Cowi has estimated that between 50% to 75% of the carbon footprint from tunnel construction comes from concrete and steel, and most of that carbon footprint comes from heating in the process of producing the material. Progress has been made in designs that reduce the
amount of concrete used in segment linings and the like; better still, recent research has identified a possible
Above: Manufacturing a TBM creates a carbon footprint but its reuse over decades helps to reduce the environmental impact ALL IMAGES COURTESY OF ROBBINS 14 | Summer 2023
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