Long-term Behaviour of Piled Raft with DMW Grid on Reclaimed Land

Abstract

This paper offers a case history of a friction piled raft, supporting a four-story parking garage on reclaimed land. The subsoil consists of filled sand and alluvial loose sand which have the potential for liquefaction. Hence, grid-form cement deep mixing walls were employed as a countermeasure of liquefaction with the piled raft. Below the sand layers, there are very-soft to medium alluvial clay layers, which are normally consolidated or under-consolidated, and the depth of the dense sand layer changes markedly near the center of the site. To reduce the differential settlement due to consolidation of the clay, 152 friction piles of different length were employed. To corroborate the foundation design, field monitoring on the foundation settlement and the load sharing between the piles and the raft was performed. The measured settlements and the maximum angular rotation of the raft about 12 years after the end of the construction were within acceptable limits. Furthermore, at the time of the 2011 off the Pacific coast of Tohoku Earthquake, no significant change in effective contact pressure between the raft and the unimproved sand was observed after the event, which confirms that the effectiveness of the grid-form DMWs as a countermeasure of liquefaction.