By Emily Newton
Tunneling projects can be tremendously resource-intensive, meaning the people leading them must proactively look for ways to make them more sustainable. Fortunately, there are plenty of options to pursue.
Since tunnels require large volumes of materials, a good starting point is to see how people might reduce the associated environmental burdens. One of them involves Germany’s Stuttgart 21 railway project. Some of the primary aims of the work are to cut the travel times for passengers on regional and long-distance routes.
The work encompasses eight tunnels, collectively spanning more than 55 kilometers, including some running under an airport and television tower. The sustainability aspect comes into play with a cement product that uses less clinker than conventional options. Estimates suggest it could save approximately 160,000 tons of CO2 or about 45% of the cement-related emissions associated with the total project. Decision-makers chose to line the inner tunnel with the lower-clinker material.
Elsewhere, Australia’s Metro Tunnel project will stand out for sustainability by using crushed recycled glass in place of 25% of the sand in the structural concrete. Virgin sand is usually mined or taken from rivers. However, using crushed glass as a substitute diverts the material from landfills. This is the first high-strength project to use a glass-sand mix in Australia, although other places in the country have used it for low-strength initiatives, such as sidewalks.
People can also be more mindful of a tunneling project’s sustainability by examining how it will affect the surrounding environment. Then, they can use the information to plan mitigation measures.
In California, the Department of Water Resources released an environmental impact report near the end of 2023 to quantify the expected impacts of the planned Delta Tunnel. It would be 45 feet in diameter and divert as much as 6,000 cubic feet of water from the Sacramento River every second.
California Governor Gavin Newsom has positioned the project as climate-related, asserting how important it will be for protecting millions of people’s access to water. However, environmental activists have heavily criticized the project, saying it will worsen an existing crisis for local fish populations. Many conservation groups collaborated to document several major flaws with the planned tunnel. Since the tunnel’s planned completion date is in 2040, there’s enough time to study and listen to concerns and then make mutually beneficial changes.
Tunneling projects can even get delayed if people don’t accommodate environmental needs during the work. Such is the case with an Australian hydropower project. Using a tunnel boring machine at the site caused a 9-meter surface depression and temporarily stopped the project. In May 2023, a report accused it of failing to comply with many of the 125 conditions of approval. Plus, 10 of the 16 required management plan submissions are overdue by years.
All these issues could significantly push back the planned completion date. When those leading a tunneling project show they’re genuinely committed to minimizing environmental requirements and following all requirements, their work should be greener. It also has a higher chance of finishing on time and free of problems.
Tunnel boring machines (TBM) are essential for excavation tasks. Keeping equipment well-maintained is an excellent way to prioritize sustainability. People can also explore the many recent TBM improvements that could help projects progress faster and more smoothly.
One company’s method allows continuous tunneling in soft ground to happen 1.6 times faster than traditional options allow. Other businesses are moving into autonomous and sensor-driven TBM technologies that give customers better control and oversight of all operation aspects.
However, it’s understandable if many leaders don’t want to or can’t immediately budget for these upgrades, even if they recognize the associated benefits. The next best thing is to explore equipment leasing opportunities. They allow people to spread the costs over many years, making the expenses much more manageable.
Using newer equipment for construction projects can reduce emissions and fuel use, making the work greener and more future-focused.
Thinking sustainably about tunneling projects also means considering the greenest ways to move excavated materials from the site. Managers supervising London’s 1.4-kilometer Silvertown Tunnel project took that approach. As of October 2021, more than 120,000 tons had arrived at or left the work area on barges. The amount was equivalent to 6,750 truckloads.
People involved with the excavation said although the River Thames’ barges weren’t the cleanest transport methods in general, they were better than using heavy trucks and the area’s roadways to move the materials. The next step is to analyze the barge movements and how to make the river traffic greener.
Many of the materials taken away with barges will have greener uses later, too. They include the reuse of several thousand tons of concrete from tunnel-related demolitions and a commitment to find beneficial applications for 1 million tons of soil.
These examples show what’s possible when people get creative about material movement. It’s an often overlooked way to make projects greener and get meaningful results.
Digital twins are highly realistic and detailed models of real-life assets. Although many people have used them for product design and manufacturing projects, they’re equally valuable for planning tunnels.
People are working on one for upgrades for London’s Piccadilly tube line. One daunting aspect of the project is a goal to make the enhancements while keeping the route operational.
Those associated with Transport for London — the organization overseeing the upgrades — hope to use the digital twin to visualize the associated emissions and work towards meeting a net-zero goal by 2030. They also believe the digital twin will keep construction and maintenance projects on schedule.
Parts of the Piccadilly line are as many as 30 meters underground in some parts and include numerous circular tunnels. However, the significant depths result in spotty Wi-Fi and GPS coverage, historically making it difficult to create digital maps of the area. Plus, surveying activities must only occur during a designated four-hour time frame.
However, the digital twin could allow surveying to happen in a different, non-time-restricted way that does not disrupt the transit line’s usage. A detailed site model could help leaders make more sustainable decisions based on the greater visibility they enjoy.
Even the most carefully planned tunneling projects disrupt the environment. However, decision-makers should do everything feasible to limit those adverse effects. These suggestions and real-life examples will give them some actionable inspiration.
Emily Newton is a construction and industrial journalist. She enjoys exploring the impact technology has in the construction and utilities sectors. When Emily isn’t writing, she enjoys building Lego sets with her husband.