tunneling

Tunneling is the practice of creating underground passages by excavating soil or rock and providing permanent support. Tunnels are used to carry transportation, water and wastewater, utilities, or storage, and are designed to withstand earth pressures and groundwater. The work requires careful geological investigation, ground stabilization, and robust lining to ensure long-term stability and safety.

Two broad approaches are used. Bored tunnels are formed by removing material from a preformed axis, typically with tunnel boring machines or drill-and-blast methods, depending on geology. The lining is installed as the excavation proceeds, often using segmented concrete rings or cast-in-place concrete. Cut-and-cover tunnels are built by excavating a trench from the surface, constructing the tunnel within or beneath the trench, and then reinstating the surface. For underwater or cross-water routes, immersed-tube tunnels use prefabricated sections laid on the seabed or riverbed and connected underwater.

Modern tunneling relies on specialized equipment and methods to manage ground conditions, water ingress, and settlement. Ground support may include shotcrete, rock bolts, steel ribs, and concrete linings. Special tunneling methods such as earth pressure balance or slurry TBMs, and the New Austrian Tunneling Method, are designed to adapt to varied soils and rock. Maintenance and monitoring address deformation, leakage, and structural integrity throughout the tunnel’s life.

Applications span transportation (road, rail, metro), utilities (water, sewage, electrical, fiber), and mining or access passages. Tunneling has evolved from manual digging in ancient times to highly engineered projects that enable efficient, safe, and durable underground infrastructure on a large scale.