Cutandcover

Cut-and-cover is a method of constructing shallow tunnels and underground structures by excavating a wide trench along the proposed route, building the tunnel structure within the trench, and then covering it with backfill and restoring the surface. It is commonly used for urban rail lines and large utility tunnels where a bored tunnel would be too deep or disruptive at ground level.

The typical sequence involves surface disruption to dig a trench, installing temporary supports or sheet piles, constructing the tunnel's lining and deck in the trench, placing tracks or roadways as needed, and then backfilling and restoring the surface once the structure is complete. In some cases, a top-down variant allows constructing the final surface layer before excavation of the lower parts, reducing surface disturbance.

Applications include subways and light-rail lines, city-center road tunnels, and major utility conduits. It is favored where there is adequate surface width or existing right-of-way, and where groundwater is manageable with dewatering and drainage. It is less suitable in areas with heavy groundwater, high surface traffic, or strict surface-use constraints.

Advantages include lower cost and simpler equipment compared with deep bored tunneling, the ability to work from the surface and to integrate with existing streets and utilities. Disadvantages include substantial surface disruption, noise, dust, risk to nearby structures, and limitations on achievable depth and tunnel cross-section.

Historically, cut-and-cover was widely used for early urban rail networks in many cities, such as parts of New York City's subway system and central sections of London's early underground lines, as well as similar projects in Paris and Tokyo.