Ground improvement for deep excavation of City Square Mall

Abstract

A commercial development, named "City Square Mall" with 4 basements, was constructed at Kitchener Road, in Singapore. Deep excavation of 18m depth was carried out in very soft marine clay and loose sands of the Kallang Formation. In order to minimize the effects of ground movements on adjacent roads and buildings, ground improvement using 3m thick grouted improved soil (GMP), and the semi-top down construction method was adopted. The construction was completed successfully. The movements of retaining wall systems and ground settlements are much less than what was initially estimated at design stage. Back-analysis with 2D-FEM can reduce computed displacements closer to measured data, but could not replicate the deflected shape of the walls. It appears that 3D effects of a square-like excavation pit with a thick stiff improved soil base layer has very significant influence on the wall deflected shape. 3D-FEM analysis is done to illustrate this behavior at "City Square Mall". Copyright © 2009 by Geotechnical Society of Singapore (GeoSS).