Field-scale constructability evaluation of underwater vacuum preloading

There is an ever-increasing demand for land to cope with the rapid economic development worldwide. As a result, new land is always reclaimed from the sea to meet the demand. The soft marine deposit in the seabed is often too weak to support the reclamation and the infrastructure to be built upon it. However, dredging of marine deposit has to be minimized to prevent ecological damage to the marine environment. In-situ improvement of the marine deposit is thus often required. Vacuum preloading is a proven technique to improve the engineering properties of soft clay onshore. However, the viability of applying the technique underwater is yet to be established. Practicality and constructability are important issues. The results of a field-scale constructability evaluation of underwater vacuum preloading are presented in the paper. Different techniques to install a membrane underwater to provide the required air-proof barrier were evaluated by monitoring the vacuum pressure underneath the membrane, pore pressure in the clay in the seabed, and ground settlement as a function of treatment duration