By P B Attewell, I W Farmer and N H Glossop, University of Durham
This paper was first published in GE’s November 1978 issue
Ground deformation measurements around a 4.25m (excavated), 3.96m (intemal) diameter shield-driven tunnel at an axis depth of 13.375m in soft, saturated silty alluvial clay has indicated two types of movement. There was an initial ground-loss movement while the tunnel face was supported by compressed air. This was typical of predominantly undrained deformation, the silty alluvium being able to displace into the tunnel. Further deformation on completion of construction and removal of compressed air support is interpreted as being due to ground consolidation, the presence of the tunnel having created a facility for moisture movement from the covering ground.