International Association of Dredging Companies IADC, in its latest edition of Terra et Aqua, has posted an article about the subsoil improvement works at Dinh Vu Industrial Zone, Haiphong, Vietnam.
This article describes the subsoil improvement works realised in the Dinh Vu Industrial Zone. This area is located along the Cam and Bach Dang Rivers adjacent to the sea.
Before land reclamation, the area was below the water level of a pond. The land was reclaimed by using sand dredged from the sea and pumped into the area to be reclaimed (thickness of the sand 3 m). The subsoil in Dinh Vu consists of soft alluvial and marine clay deposits with a thickness of about 35 m.
The soft subsoil has low bearing capacity and excessive settlement characteristics.
In order to accelerate the settlement process, subsoil consolidation has been performed in an area of 40 ha in the industrial zone, including installation of prefabricated vertical drains (PVDs) combined with a surcharge preloading. PVDs provide a shorter drainage path in a radial direction which decreases the excess pore pressure and increases the effective stress. In order to realise the design of PVDs (spacing and depth), a pre-soil investigation was performed and theoretical predictions of settlement were calculated.
During the project the consolidation process was recorded with settlement marker plates. Settlement recordings have been analysed using the Asaoka method. Theoretical consolidation behaviour predicted before subsoil improvement matched the recorded consolidation.
A model was developed and in order to test its accuracy under different loads, a trial embankment was performed (thickness of sand 6 m). A post-soil investigation has also been realised and compared to the pre-soil investigation highlighting the subsoil improvement.
Press Release, December 11, 2013