Summary Draft #4

 Designed to have superior performance while remaining safe during underground excavation, the Herrenknecht Tunnel Boring Machine (TBM) is a state-of-the-art piece of engineering (Herrenknecht, n.d., Our Tunnelling Technology section). called the cutter head located at the forefront, equipped with disc cutters or other cutting tools designed to break rock and soil as it advances (Wikipedia, 2024). According to Wikipedia (2024), TBMs also feature a conveyor system, which consists of belt conveyors or screw conveyors to collect and remove excavated material, also referred to as "muck", from the tunnel face. During tunnelling, TBMs also possess advanced guidance systems to maintain precise alignment. These systems usually utilize laser-based technology, consisting of a laser theodolite and a laser target to create a navigation system that can steer the machine accurately. (Herrenknecht, n.d.). TBMs ability to propel itself forward is due to its hydraulic thrust cylinders, which push against the tunnel walls. These cylinders are positioned around the circumference of the TBM, pushing the machine forward from previously dug tunnel walls (Herrenknecht, n.d.).

TBMs significantly enhance the accuracy and efficiency of tunnel construction compared to traditional methods like drill and blast; however, their large size and logistical challenges may make traditional techniques more suitable in certain niche situations.

First of all, TBMs greatly enhance the efficiency of tunnelling projects, enabling faster completion compared to traditional methods. Encardio (2019) reports that TBMs can usually excavate about 50 to 60 feet per day with their high-speed which is approximately 20 hours of constant excavation. This continuous operation minimizes downtime, further improving efficiency and maximizing the amount of time saved (Tunnel Engineering, 2024). In contrast, traditional methods like the drill and blast method typically excavate at a rate of only 3 to 5 meters per day (Railsystem.net, n.d.). For example, a tunnelling project that would typically take 15 days to complete using traditional methods can be finished in just 5 days with a TBM, illustrating the substantial amount of time TBMs could save. Thus, the superior efficiency of modern TBMs makes them the preferred choice for projects requiring swift completion.

While TBMs have significant advantages in terms of accuracy and efficiency, their large size and complex logistics can make traditional methods, such as drill and blast, a more reasonable choice for confined tunnelling projects. For instance, a TBM used in Poland weighed 4,300 tons, measured 107 meters in length, and featured a tunnelling disc with a diameter of 15.2 meters (DB Schenker, 2023). TBMs with such sizes require specialized transportation, such as unique semi-trailers and allocating expressway exits, to ensure their safe delivery. In contrast, traditional tunnelling methods like drill and blast are more adaptable to various site conditions, such as cavern construction, cross-overs, cross passages, shafts, and penstocks, making them appropriate for projects where TBMs may not be usable (Tunneling Online, 2020). The substantial size and complex logistics required for transporting a TBM, as illustrated by the case in Poland, highlight the significant issues associated with its deployment, especially in projects with limited access or confined spaces. This evidence reinforces the argument that traditional methods, like drill and blast, are often more practical for smaller-scale or more site-restricted tunnelling projects, where TBMs may not be a viable option.

In conclusion, TBMs undoubtedly offer superior efficiency and precision, making them the preferred choice for large-scale tunnelling projects where these qualities are essential. Their advanced technology ensures minimal deviation and consistent alignment, significantly reducing the need for costly corrections compared to traditional methods. However, the logistical challenges posed by their massive size and transportation requirements can make traditional techniques, like drill and blast, more suitable for smaller-scale or confined projects. Despite this limitation, the overall advantages of TBMs in terms of accuracy and efficiency make them a groundbreaking tool in modern tunnelling, often outweighing the drawbacks, especially for major infrastructure endeavours.

References:

DB Schenker. (2023, October 7). Unique TBM (Tunnel Boring Machine) transport logistics. https://www.dbschenker.com/global/insights/blog/unique-tbm-tunnel-boring-machine-1677782

Encardio. (2019, March 13). All about tunnel boring machine: Components, types, and advantages. https://www.encardio.com/blog/all-about-tunnel-boring-machine-components-types-advantages

Herrenknecht. (n.d.). Our tunnelling technology. https://www.herrenknecht.com

JOUAV. (2024, March 27). Drilling and blasting: Principles and applications. Retrieved from https://www.jouav.com/blog/drilling-and-blasting.html

Railsystem.net. (n.d.). Drill and blast method. https://railsystem.net/drill-and-blast-method

Tunnel Engineering. (2024, September 20). Comparison between TBM tunnelling and drill and blast method in hard rock tunnels. https://tunnel.engineering/comparison-between-tbm-tunnelling-and-drill-and-blast-method-in-hard-rock-tunnels

Tunneling Online. (2020, April 15). Advancements in tunneling and underground excavation by drill & blast. https://tunnelingonline.com/advancements-in-tunneling-and-underground-excavation-by-drill-blast

Wikipedia. (2024,). Tunnel boring machine. https://en.wikipedia.org/wiki/Tunnel_boring_machine