Study of Seepage Flow And Sand Plug Loosening In Installation of Suction Caissons In Sand

It is well known that seepage flow plays a key role in assisting suction installation of caissons in sand. By loosening sand along the caisson’s inner wall and at the wall tip, the flow significantly reduces the soil resistance. At the same time, this can also create plug loosening and upward movement of the sand column inside the caisson. Despite being widely observed in both field tests and small-scale experimental studies, the behaviour of seepage flow and the extent of sand plug loosening during suction installation are not well understood. To investigate the problem, a series of tests were conducted in a geotechnical centrifuge. Seepage flow during each test was derived and compared with results from the 1g tests. Theoretical seepage was also calculated using PLAXIS, whose results were then compared with the experimental ones. The extent of plug loosening in the tests was examined through seepage back-calculations, and checked against the recorded sand heave using a previously developed void ratiopermeability relationship. It was found that the initially dense sand plug appeared to be in medium state during installation. Comparisons between theoretical expansion and recorded heave gave good agreement. CPT tests were also conducted inside the suction-installed caissons, and clearly showed evidence of plug loosening. The tests were carried out using caissons of different sizes. Scaling of seepage flow in the centrifuge will also be discussed.