Summary Final Draft

 Designed to be the top-of-line excavation machine, the Herrenknecht Tunnel Boring Machine (TBM) is made to have exceptional performance underground while remaining safe (Herrenknecht, n.d., Our Tunnelling Technology section). Key features of a modern TBM include the cutter head, conveyor system, navigation system and hydraulic thrust cylinders. Located at the forefront of the TBM is the cutter head equipped with disc cutters and other cutting tools engineered to break rock and soil as it advances (Wikipedia, 2024). According to Wikipedia (2024), TBMs’ conveyor system consists of belt conveyors or screw conveyors to collect and remove excavated material, also referred to as “muck”, from the tunnel face. While excavating, TBMs use their advanced navigation systems to maintain precise alignment. Utilizing laser-based technology consisting of a laser theodolite and a laser target, these navigation systems are able to steer the machine accurately (Herrenknecht, n.d.). TBMs ability to propel themselves forward is due to their hydraulic thrust cylinders, which push against the tunnel walls. These cylinders are positioned around the circumference of the TBM, pushing the machine forward from the 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 methods more suitable in certain niche situations.

First of all, TBMs greatly enhance the efficiency of tunneling projects, enabling faster completion compared to traditional methods. Encardio (2019) reports that TBMs with their high speeds can usually excavate approximately 50 to 60 feet in a day, which is roughly 20 hours of constant operation. Staying operational constantly, TBMs are able to reduce downtime to a minimum, further improving efficiency and productivity (Tunnel, 2024). In contrast, traditional methods like drill and blast can only typically achieve a rate of 3 to 5 meters a day (Railsystem.net, n.d.). For example, a tunneling project that would take roughly 15 days for blast and drill to complete, TBMs can finish excavation in just 5 days, demonstrating the substantial amount of time TBMs could save. Thus, modern TBMs with their superior efficiency, make them the preferred choice for projects requiring swift completion.

Also, unlike traditional tunneling methods, modern TBMs leverage cutting-edge technology to navigate underground with unmatched precision, ensuring that tunnels are excavated accurately with minimal deviation. With the help of their laser-based navigation systems, including a laser theodolite that tracks the position of the TBM underground, aligning TBMs to their planned tunnel axis, ensuring accurate excavation lines (Herrenknecht, n.d.). On the other hand, the inaccurate nature of traditional methods like drill and blast creates cracks past the intended excavation path, resulting in the need for additional measures to fix errors and wasted materials (JOUAV, 2024). This demonstrates the difference between the two methods, with TBMs having accurately excavated lines compared to drill and blast error-prone excavation. Thus, TBMs with the use of advanced laser technology, have a significant advantage over traditional methods.

While TBMs have notable advantages over traditional methods in terms of accuracy and efficiency, due to their large size and complex logistics, traditional methods can be a more reasonable choice in niche situations. For instance, a project in Poland used a TBM that measured 107 meters in length, featured a tunneling disc with a diameter of 15.2 meters and weighed 4,300 tons (DB Schenker, 2023). The size of TBMs requires them to have unique ways of transporting them, such as allocating expressway exits and special semi-trailers, to ensure their safe delivery. In contrast, traditional tunneling methods like drill and blast are more flexible to a vast number of site conditions, including but not limited to cavern construction, cross-overs, cross passages, shafts and penstocks, making them the wise choice for projects where TBMs are not usable (Jennemyr, 2020). Due to their size and complex logistics, as shown by the case in Poland. TBMs have many issues surrounding its deployment, especially in projects where limited space is one of the various site conditions. This allows traditional methods like drill and blast to become a more reasonable choice for more site-restricted tunneling projects, where TBMs may not be a viable option.

In conclusion, TBMs undoubtedly offer unmatched efficiency and precision, making them the favored choice for large-scale tunneling projects where such qualities are essential. Their use of advanced technology ensures consistent accuracy and minimal errors, removing the need for costly corrections compared to traditional methods. However, the issues surrounding their deployment due to their size and complex transportation can make traditional methods, like drill and blast, more suitable for small-scale or space-restricted projects. Despite this limitation, the overall advantages that TBMs provide in both efficiency and precision make them an irreplaceable tool in modern tunneling, especially for major infrastructure projects.

(I hereby acknowledge the usage of ChatGPT for error checking and sourcing of information for this Reader’s Response)

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. (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

Lars Jennemyr. (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