Wick drains and piling for Cai Mep container port, Vietnam

Abstract

A container terminal, Cai Mep port in the Mekong delta approximately 80 km southeast of Ho Chi Minh City, Vietnam, was constructed along the Thi Vai River over about 35 m thick soft, deltaic silty clay deposited on dense to compact sand. The port buildings required piled-raft foundations, which were 400-mm square, precast concrete piles driven to 18–28 m depth. One building required 760 piles. The seasonal flooding conditions in the area required raising the ground surface by 2.5 m, which brought about considerable consolidation settlement. To ensure that the settlement would develop before constructing the port area and buildings, the consolidation was accelerated by means of wick drains at a spacing of about 1.2 m. Additional fill (surcharge) was placed to raise the ground to a total height of 8–10 m. The surcharge was kept on for 6–18 months at which time the consolidation was considered to have completed and the piles were constructed. The settlements and amounted to about 3.5 m during the surcharge period. Settlement monitoring continued after end of surcharge removal and it became obvious that the area continued to settle after the removal of the surcharge, indicating that consolidation settlement had not been completed despite the long surcharge period. Indeed, the post-construction settlement over general port area would exceed the specified limit: 400 mm over a 20-year period. Moreover, which was rather perplexing, when monitoring the settlement of the piled foundations after the pile construction, the piles were found to settle at the same rate as the ground surface already before the buildings had been constructed. A remedial procedure was implemented that involved extending the piles to bear in the sand, where no long-term settlement would occur. The problem and its solution were analyzed by means of the unified design method. The remedial solution did not resolve the settlement problem for the general container storage area, however.