Abstract
The Old Alluvium (OA) in Singapore is a quartenary alluvial deposit consisting of mainly medium to very dense cemented clayey quatzo-feldspathic sands and fine gravels with some coarse gravel and lenses of silt and clay (Pitts, 1984). Previous attempts to define the engineering properties of the OA from soil tests have met with limited success due to the vast scatter in the results resulting conservative assumptions of soil parameters for design of earth retaining structures. Consequently, the observed performance of recent deep excavations works in the OA shows a significant deviation from the predicted performance. Amongst the various reasons that could account for the deviation of actual field performance, one major factor was inability of conventional testing methods to derive stress-strain behaviour of soil at smaller strain level. In this paper, the ensuing investigations to measure the small strain stiffness behaviour of the Singapore OA soils from laboratory and field tests are presented. PS suspension logging tests are conducted to interpret the small strain stiffness of the soil in the field in-situ. Bender element tests in triaxial set up are conducted on undisturbed samples to determine the small strain stiffness of soil in the laboratory.
