How big are underground tunnel machines? Underground tunnel boring machines, also known as TBMs, come in a wide range of sizes depending on the specific needs of the project they are designed for. These machines are engineering marvels, capable of excavating through various types of soil and rock to create tunnels for subways, roads, water systems, and other infrastructure.

　　Size Range

　　- Small TBMs: These can have diameters as small as a few meters (around 2 to 4meters). They are typically used for utility tunnels and smaller-scale projects.

　　- Medium TBMs: These have diameters ranging from about 5 to 10 meters. They are commonly used for subway tunnels and large utility projects.

　　- Large TBMs: These machines can have diameters of 10 meters or more. The largest TBMs ever built have diameters exceeding 15 meters. The "Bertha" TBM.

　　Used in the Alaskan Way Viaduct replacement tunnel in Seattle, had a diameter of 17.48 meters, making it one of the largest ever constructed.

　　The size of a TBM is determined by the project it is designed for. From small utility tunnels to massive subway projects, these machines are essential tools in modern construction, pushing the boundaries of what is possible in underground engineering. Their sheer scale and technological sophistication continue to evolve, making them a fascinating subject for both engineers and enthusiasts alike.