Despite a daunting timeline set by the Paris Accord, zero-carbon tunnels are within reach, provided the right solutions are implemented.
Er. Vasileios (Bill) Paoulos, CMT, CMRL, L&T Construction Heavy Civil Infrastructure
The tunnelling industry is at a tipping point where sustainability and decarbonization are at the top of the executives’ agendas. To achieve a 1.5°c climate-change target by 2050, the tunnelling industry will need to play its own role to reduce direct CO2 emissions to net zero.
Currently, only few countries and infrastructure projects are “walking the talk” and taking the initiative to reduce carbon emissions. Perhaps Norway is one country leading the way; with their world leading domestic electric vehicle market, electric drive construction equipment is increasingly being employed. Norway’s major cities are to witness carbon neutral construction by 2025.
Outside Norway, a few countries and projects in Europe are establishing some aspirational targets to reduce carbon, but typically with the sole focus of developing lower carbon concrete mixes.
The tunnelling industry, which is a contributor to global CO2 emissions, is facing increasing pressure from policy makers, investors, and customers to decarbonize operations. Whilst some believe low carbon tunnelling automatically equates to higher project costs, the best practices in carbon management in the construction industry suggest otherwise. A holistic approach throughout a project’s lifetime, with engineers focused on carbon saving, can intrinsically deliver an overall project cost saving too. This is the ethos behind the PAS 2080 approach to Carbon Management in Infrastructure and is well worth employing on projects for those keen on decarbonization.
Given the growing need for decarbonization, my advice is to consider 3 key aspects that would accelerate decarbonation efforts and make a considerable push forward to achieve the 1.5°C climate-change goal: Build Clever, Build Efficiently, and Build for a Lifetime.
Build Clever: It all starts with innovative and considerate design
The biggest decarbonization gains in tunnels come from decisions at the planning and design stage. For instance, upfront choices for possible projects are crucial to the carbon story, including whether to build at all, or look to upgrade, or extend the life of existing assets, before pursuing a new build approach.
As always with any project, it is early in the design stage that the key differences are made; and in tunnels it is design where the largest proportion of savings in carbon can be made. Such design benefits can be more readily implemented on tunnel projects through client leadership, for example, incentivising procurement approaches that attract main contractors to offer innovative carbon reducing processes and materials, that in turn stimulate the wider technical supply chain.
In open face tunnelling, sprayed concrete rock support is used globally. In many countries (given its high quality), it has been widely adopted for permanent tunnel linings, which save between 20- 25% of the concrete used in conventional tunnel lining systems. I believe that modern sprayed concrete systems today, combining high levels of Portland Cement replacement, polymer fibres and innovative waterproofing technologies, offer possibilities to potentially achieve up to 50% reduction in carbon in our tunnel linings. But again, these Build Clever solutions must be captured and implemented at the early design stage to maximise the biggest carbon saving potential. These are real solutions for real savings; we can take these big steps today with the right team culture and the right design, coupled with exciting new procurement models to coerce positive changes.
As a side note, the challenge for the low carbon sprayed concrete is the slower strength gain in the first few hours after spraying. Early strength gain is vital for overhead safety and productivity in building thick enough layers. Interesting studies that we have developed with geopolymers (mixes with no Portland cement) have shown that we can obtain ultra-low carbon concrete with rapid early strength gain. However, we continue to improve the desired long-term performance to make these mixes more viable.
The next step we can take towards carbon zero tunnels is to be super-efficient throughout the construction processes.
Build Efficiently: Smart equipment, people, and digitalisation
Multiple efforts will be required to address the principal sources of emissions and to decarbonize. Efforts include a move towards sustainable sourcing, selective use of fuels, electric drivetrains, as well as a switch to green electricity providers to power tunnel construction projects.
An example of our sustainable offering is the SmartDrive battery electric vehicles which provide improved performance with zero local emissions. They also eliminate fuel and fuel transportation costs and have lower equipment maintenance costs.
Norwegian tunnel contractors are already operating to 2050 carbon net zero targets by using SmartDrive Spraymec 8100 SD spraying robots that are charged using hydropower grid electricity. We are now starting to see this in remote mining projects where mine based renewable energy plants supply the battery charging power for the mining equipment fleet.
Critical to carbon reduction is to start measuring and establishing our carbon usage in tunnelling projects today. We need to create a baseline on which to benchmark - a reference point to improve our game. To do this, I anticipate a digital revolution in sprayed concrete tunnelling, using data access platforms that pull in data sources from underground equipment, batch plants etc, but also intelligent and real-time 3D scanning systems at the excavation face, supporting robot nozzle operators “getting it right first time” when they can spray to the required profile or thickness.
These systems will also support engineers to assess material usage, geology, and quality. In essence, a real-time digital twin will be highly valuable to all stakeholders and will drive the daily review of carbon and cost reduction, whilst attaining controlled, safe processes.
Virtual reality training platforms for key operators are becoming established in our industry. Normet’s VR Sprayed Concrete Simulator, endorsed by the international EFNARC C2 certification scheme, is the latest example allowing nozzle operators to hone their skills in the classroom environment. These simulators encourage safe, sustainable ways of spraying and highlight areas for improvement, helping trainees to develop the right attitude and follow safe practices needed in the underground space.
Build for a lifetime
We need to be less of a throwaway society - even in tunnelling! Normet builds equipment to last; wherever we can, we recycle and re-purpose our components and materials to build new equipment and new construction materials.
Furthermore, when you choose not to build new tunnels, we can offer ways to give new operational life to tired and worn out existing underground assets, by first using remote, accurate structure assessment tools to define the issues, then an array of smart, fast track rehabilitating technologies and processes to fix things ready for another lease of life.
Finally, let’s promote the use of low carbon sprayed concrete technologies to build more sustainable infrastructure. High societal value is already measurable with the re-invigorated interest in underground green energy storage schemes, such as with pumped hydro and future hydrogen storage, but also low project cost tunnel solutions.
In a nutshell, multiple efforts on various fronts are needed to accelerate decarbonation efforts in tunnelling. It’s not just about low carbon concrete. We’ve all got some work to do, so let’s get to it and have fit “low-carb” tunnels!
Key References
- Melbye,T,2022.MUIRWOOD LECTURE: Wet -Mix Sprayed Concrete -A Modern Support Method in Tunnelling and Mining. ITA-AITES World Tunnel Congress, WTC2020 Malaysia May 2020(postponed).
- Grov, E.2021. SUPERCON-Sprayed sustainable permanent robotized concrete tunnel lining. NFF Rock Blasting Conference, Oslo November 2021.ISBN 978-82-8208-076-7
- Bowers, K,2020.BTS Harding Prize Lecture, London, UK.
- Thomas, A,2020.Achieving sustainability in underground construction through innovation. ICE publishing, London, UK.
- PAS 2080:2016-Carbon Management in Infrastructure. The British Standards Institution 2016.Published by British Standards Limited 2016. ISBN 978 0 580 90155 3
- The GREEN BOOK-Central Government Guidance on Appraisal and Evaluation(2020).Crown copyright 2018.This Publication is available at www.gov.uk/official-documents
- UK Committee on Climate Change 2020.Reducing UK emissions-Progress Report to Parliament-June 2020. Published www.theccc.org.uk/publications.
- Myrdal, R&Griffith, R 2014. Admixtures for geopolymer concrete:the performance of accelerating admixtures, Proceedings of the 2nd International Congress on Durability Of Concrete.
He has also acquired a wide operational experience in pre-selection, evaluation and operation/managing, production efficiency and product quality assurance for project related Quarries, Crushers, Batching Plants and Pre-Fabrication Lines.
He is a professional chartered engineer, and active contributor as a Member of the Technical Chamber of Greece (T.E.E.). Paoulos completed his Master of Civil & Structural Engineering (MEng) from UMIST (University of Manchester Institute of Science and Technology) and Post Graduate Dipl. in Blast and Ballistic Loading Structural Response and Design from RMCS (Royal Military College of Science) affiliated to Cranfield University.
