The impact of shallow cover on tunnelling in soft soil

Abstract: Shield tunnelling is used widely in constructing underground infrastructure in cities due to the ability to limit settlements and damage to existing buildings. However, in an environment with soft overburden and buildings on pile foundations, the tunnel is often designed well below the pile tip level. There are two reasons for doing this: to reduce interaction between tunnelling process and piles, and to avoid having to drive through old abandoned piles that are still present below the streets. This results in deep station boxes. When the tunnels would be located at a more shallow level above the pile tip level, this would largely eliminate the impact on pile bearing capacity as well as reduce the required depth of the station boxes and the construction cost.