Study of Seepage Flow and Sand Plug Loosening in Installation of Suction Caissons in Sand

摘要

It is well known that seepage flow plays a key role in assisting suctionrninstallation of caissons in sand. By loosening sand along the caisson’srninner wall and at the wall tip, the flow significantly reduces the soilrnresistance. At the same time, this can also create plug loosening andrnupward movement of the sand column inside the caisson. Despite beingrnwidely observed in both field tests and small-scale experimentalrnstudies, the behaviour of seepage flow and the extent of sand plugrnloosening during suction installation are not well understood. Torninvestigate the problem, a series of tests were conducted in arngeotechnical centrifuge. Seepage flow during each test was derived andrncompared with results from the 1g tests. Theoretical seepage was alsorncalculated using PLAXIS, whose results were then compared with thernexperimental ones. The extent of plug loosening in the tests wasrnexamined through seepage back-calculations, and checked against thernrecorded sand heave using a previously developed void ratiopermeabilityrnrelationship. It was found that the initially dense sand plugrnappeared to be in medium state during installation. Comparisonsrnbetween theoretical expansion and recorded heave gave goodrnagreement. CPT tests were also conducted inside the suction-installedrncaissons, and clearly showed evidence of plug loosening. The testsrnwere carried out using caissons of different sizes. Scaling of seepagernflow in the centrifuge will also be discussed.