Prefabricated vertical-drain test section in Craney Island Dredged Material Management Area

A 183 m by 122 m prefabricated vertical-drain test section was completed in February, 1993, in the Craney Island Dredged Material Management Area. The test section was constructed to evaluate the effectiveness of prefabricated vertical drains in consolidating the dredged fill and underlying foundation clay, thus increasing the storage capacity of the facility. The feasibility of installing prefabricated vertical drains was questionable because vertical drains had never been installed in an active dredged material management area; a drain length of approximately 50 m was close to the longest vertical drain ever installed, and the installation equipment could exert a ground pressure of only 10.3 kPa to operate on the surface of the soft dredged material. Results show that the dredged fill and foundation clay underwent substantial consolidation settlement (1.8 to 2.7 m in 30 months) after drain installation. In summary, prefabricated vertical drains appear to be an economical technique for increasing the storage capacity of active and inactive dredged material management areas.