Investigation on influence of tail void grouting on the surface settlements during shield tunneling using a stress-pore pressure coupled analysis

For shallow tunnel constructions, settlement of the ground surface is a main issue. Recent technical developments in shield tunneling technique have enabled a decrease in such settlements due to tunneling under ground deformation controls. However, surface settlements are still considerable. The objective of this paper is to investigate ground behavior due to grouting of the tail void in shield tunneling. Tail void grouting is a common practice in shield tunneling that reduces ground movements and changes in the stress state of the ground due to tunnel excavation. In order to investigate the influence of tail void grouting, three dimensional FEsimulations were performed for the simple case of a tunnel heading in homogeneous sandy soil below the ground water table. In a sensitivity analysis, the initial relative density of the ground, which determines the stress-strain relationship, was changed. Focusing on the stress and volume change of the tail void grout with time, the simulation results were evaluated with respect to the deformation and stress state of the ground. Surface settlement depends both on the volume loss due to tunnel construction and on the volume change of the ground around the tunnel. Additionally, such volume change is influenced by pore water pressure.