Constructing tunnels exposes workers to various dangers, which is why machines are essential. Thus, tunnel boring machines stand out as crucial equipment since they come in multiple forms that are typically used to meet the requirements of different tunnel construction methods.
As technology advances, newer and more specialized types of tunnel boring machines emerge, further enhancing safety and efficiency in tunnel construction projects.
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1. Soft Ground TBMs
Earth Pressure Balance (EPB) machines and Slurry Shield (SS) machines are the two principal types of tunneling machines (TBMs) being utilized in soft ground tunneling. Both machines, comparable to Single Shield TBMs, progress by applying propulsion against concrete segments via thrust cylinders. As mentioned, the EPB TBM is used for soft ground and pressures below 7 bar. Their cutter heads include cutting bits made of tungsten carbide, carbide disc cutters, and hard rock disc cutters. In addition, the Earth Pressure Balance machine helps achieve a state of equilibrium between the earth's pressure and the machine's pressure. Because of this, the machine can endure the soft ground that lies beneath it.
2. Hard Rock TBMs
Open-type or shielded tunnel boring machines (TBMs) may excavate unyielding rock. Compressive stress fractures are caused by the disc cutters on hard rock TBMs located within the cutter head. These fractures cause the rock to break apart, resulting in chips being removed from the tunnel face. It is then evacuated from the tunnel using a series of conveyors or muck cars. The debris produced is referred to as muck, and it is carried from the cutter head to a conveyor belt.
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3. Gripper TBM
Gripper tunnel boring machines are designed to bore rock tunnels. These machines typically employ disk cutters as excavation instruments and advance by applying shove forces against the tunnel walls via a hydraulic gripper reaction system. When no final lining is feasible, driving in conditions of unbending rock is appropriate. Accordingly, it is possible to attach the rock supports behind the cutter head shield.
These rock supports, which may include rock anchors, wire mesh, shotcrete, and steel arches, allow for the regulated alleviation of stress and movements. Even when operating in high-pressure rock, gripper TBMs are able to maintain their flexibility due to the presence of moveable partial shields, which help to prevent the machine from being jammed when digging in expanding rock.
4. Slurry Shield TBMs
Tunneling in soft, wet soils, as well as tunneling beneath rivers and other bodies of water, is how Slurry Shield TBMs are utilized. These machines use a slurry consisting of water and bentonite clay to provide support for the tunnel walls and remove the material that has been excavated. By forming a solid, stable wall along the tunnel face, the slurry is pumped to prevent tunnel collapse. Additionally, a conveyance system is integrated into Slurry Shield TBMs to remove excavated material from the tunnel, which makes them ideal for tunneling in densely populated regions.
5. Micro TBMs
Micro Tunneling Machines (MBMs) are compact tunneling machines used to excavate tunnels in tight locations such as crawl spaces, basements, and under structures. The conveyor system and diminutive cutting heads of these devices remove the tunnel's excavated material. Micro tunnel boring machines are suitable for digging in urban settings where space is restricted.
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