C+S August 2023 Vol. 9 Issue 8 (web)

The US underground construction industry is booming. Back in November 2021, President Biden signed into law a new $1.2tn (£895bn) infrastructure bill that has uplifted the prospects of construction players across the country. Described as a “once-in-a- generation” initiative, the bill helps to pave the way for a variety of ambitious projects. Chief among these is the new railroad tunnel set to be built under the Hudson River that will connect New York and New Jersey as part of Amtrack’s Gateway Program, while the bill has also renewed talk of connecting New York and Boston with a high-speed, 16-mile railroad tunnel. However, there are many similar flagship projects scattered across several states that are also coming to fruition. The $6 billion Second Avenue Subway Phase II project is also currently underway in New York, while Baltimore is set to benefit from both the $6 billion Baltimore & Potomac Tunnel Replacement and $10 billion Superconducting Maglev Project – Northeast Corridor project. Meanwhile, over on the West Coast, the $5.5 billion Silicon Valley Santa Clara Extension and $12-15 billion BART 2nd Transbay Tube continue to capture headlines in California, while Texas is set to benefit from its own $1.7 billion D2 Subway in Dallas. With that said, not all underground structures currently being built in the US are designed for large scale transportation purposes. The state of Washington is coming under pressure to address the impacts that man made structures are having on several endangered species of salmon, paving the way for the construction of several small tunnels that provide the fish free passage to migrate to the sea and back inland to spawn. Back in California, meanwhile, to address the threat of tree branches falling on power lines and creating forest fires, Pacific Gas and Electric has outlined plans to bury 10,000 miles of distribution and transmission lines in California at a cost of $15-30 billion. Exploring the massive potential for innovative underground construction technologies in the US By Patrick Lane-Nott

Taking a new approach to underground construction In every one of these projects, the sums involved are astronomical– and that presents a significant opportunity for innovation and industry disruption. For well over a century, approaches to underground construction have broadly remained the same, involving the use of tunnel boring machines (TBMs). However, this conventional practice of excavation and building comes with risk, complexity and cost, as well as a heavy carbon footprint. If we consider Pacific Gas and Electric’s own commitment, burying lines underground currently costs $1 million per mile – this is significantly more costly than hanging lines overhead, and only increases further in more difficult terrain, such as mountainous areas. Finding ways in which to make the United States’ many new underground construction projects more affordable is therefore vital. Thankfully, technological advances promise to make the construction, extension, repair, and maintenance of underground structures significantly faster, cheaper, safer, less disruptive, and more environmentally friendly. Indeed, one method involves the use of swarm robotics and in-situ construction to offer the underground construction industry more options besides the traditional processes. This new method is described as follows. First, pilot bores are drilled and lined, and robots sent inside to inspect the geology. Core samples are taken, and the geology is scanned using ground penetrating radar (GPR). The result is a near perfect understanding of the entire tunnel length’s geology. Using this data, a virtual model of the tunnel structure is developed: the digital twin. With AI and machine learning, the optimum build




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