Effect of jet-grouting on surface settlements above the Aeschertunnel, Switzerland

The Aeschertunnel is a large shallow non-circular tunnel that was excavated in glacial moraine and Molasse bedrock. In the sections, where the excavation was in the glacial moraine, the construction procedure included the use of a jet-grout arch ahead of the tunnel face for excavation support. Measurements taken during the jet-grouting process and the excavation of the tunnel heading suggested a settlement trough much narrower than that observed using conventional NATM tunneling methods. The volume losses were limited to 0.35%, approximately the volume losses achieved with slurry shield and EPB TBM tunneling. A numerical back-analysis was performed on the surface settlements where jet-grouting was used. The back-analysis suggests that the narrow settlement trough results from localized shear bands that were induced by high pressures associated with the jet-grouting.