External radial stress changes and axial capacity for suction caissons in soft clay

A series of centrifuge tests was performed on instrumented model caissons in normally consolidated, lightly over-consolidated and sensitive clays, to investigate the external radial stress changes around suction caissons during installation, consolidation and pullout, and axial capacity after consolidation. Total pressure transducers embedded at different elevations of the caisson wall showed external radial total stresses that varied almost linearly with depth during both penetration and extraction of the caisson, with smaller gradients during post-consolidation pullout. Only slight differences were found in the measured external radial total stress when pressure transducers entered the suction-affected zone from the jacking-affected zone. Comparisons are presented between measurements and two theoretical predictions, for both the external radial total stress during caisson installation, and the radial effective stress after consolidation. A simple cavity expansion approach was found to give reasonable predictions of stress changes and post-consolidation external shaft friction for caissons installed by combined self-weight and suction. These findings are consistent with estimates of the amount of internal soil heave during installation, where about 50% of the caisson wall thickness was accommodated by outward flow of soil.