Quantification of extrusion-induced excavation volume in shield tunnelling through squeezing cohesive-frictional ground.

When tunnelling through weak and highly deformable ground, relevant deformations occur ahead of the tunnel face and result in face displacements that are opposite to the advance direction ("extrusion"). In mechanised tunnelling, the cutterhead continuously removes the ground extruding at the tunnel face during advance. Therefore, the total excavation volume is higher than the volume that corresponds to the tunnel cross-section area.