tunnelboring

Tunnelboring is a method of excavating tunnels using specialized equipment, primarily tunnel boring machines (TBMs), to create underground passages for transportation, utilities, and other infrastructure. It is widely used for urban subway tunnels, road tunnels, water and wastewater conduits, and mining-related works.

The most common equipment is the tunnel boring machine, which consists of a rotating cutterhead at the front, a shield to support the surrounding ground, and a thrust system to push the machine forward. As the cutterhead excavates, the spoil is removed by conveyors or other removal systems, and a lining is installed behind the TBM to form a stable tunnel ring. TBMs are designed for different ground conditions and are categorized as hard rock TBMs, soft-ground or earth-pressure-balance TBMs, and slurry shield TBMs. Related techniques such as microtunneling and auger boring are used for smaller diameters or specific conditions.

The process involves the TBM advancing through the ground while maintaining support to prevent collapse. Excavated material is transported to the surface or a disposal area, and the lining is completed as the machine progresses. In soft ground or high-water inflow areas, grouting and ground stabilization may accompany lining work.

Advantages include continuous excavation with minimal surface disruption, smooth tunnel walls, and suitability for long or large-diameter projects. Disadvantages include high upfront costs, complex logistics, potential ground movement, and the risk of TBM downtime due to blockages or equipment failures.

Environmental and safety considerations cover groundwater management, spoil handling, noise and vibration control, and monitoring of nearby structures. Tunnelboring has enabled many large-scale urban and infrastructural projects and remains a central technique in modern civil engineering.