Stabilizing Soil with a 3-Cell Diaphragm Wall System: 18 Robinson, Singapore
Session: G: Geotechnical Engineering Award & Systems Award
Director, C & S Engineering, KTP Consultants Pte Ltd
Set on land reclaimed from the sea during the early half of the 20th century, the site had a unique set of challenges during the construction for the iconic 28-floor tower of 18 Robinson. Under some 5 meter thick of reclaimed Fill is a thin layer of sand deposit (original seabed) followed by thick Marine Clay (MC) varying from 12 meters to 30 meters across the site. Underlying the MC is Fort Canning Boulder Bedrock (FCBB) which are sandstone boulders embedded in hard reddish/ brownish clay matrix.
The proposed 6 levels of basement at 22 meters depth (72 feet) reaches close to 4 meters in distance to a pair of Mass Rapid Transit underground tunnel that are non-suspended and floating in the Marine Clay. After careful evaluation on all aspects, the solution was the form of 3 cellular cells of varying diameters arranged from large to small with a diaphragm wall construction that would fit within the site. The system has the benefits of high hoop stiffness crucial to minimize ground deformation and the resulting movements of existing tunnels from the basement excavations.
The basement 3-cell Dwall system played a key role in the construction of the building. It maximized the basement area by providing a stable excavation and allowed a full top-down construction sequence without the use of any temporary shoring, thus minimizing time and cost of the excavation while having no adverse impact on the progress of the superstructure. The system proves to be rigid and effective even with the close proximity to the pair of MRT tunnels in Marine Clay.