Have You Heard of Stacked Drifts?

The use of “stacked drifts” in the sequential excavation method of tunnelling has been employed for over four decades and has allowed for the construction of tunnels and underground caverns approaching nearly 30-m width under clear cover thickness of 5 m or less, more typically in soft ground geology. The method essentially involves constructing a series of smaller-diameter tunnels, configured side-by-side, arched, and/or vertically “stacked.” Typically, each small tunnel is backfilled with concrete and linked to adjacent tunnels with mechanical or shear interlocks to either directly form or facilitate the construction of a single, larger-diameter tunnel or underground cavity.