SETTLEMENT AND BEARING CAPACITY OF FOUNDATIONS IN SINGAPORE RESIDUAL SOILS AND OLD ALLUVIUM

Abstract

The residual soils of Singapore are mainly of granitic and sedimentary origin, ranging from silty sand to silty clay, depending on the composition of the parent rock. The Old Alluvium formation, which general) comprises poorly-graded medium dense to dense clayey coarse sand, or less often sandy clay, is the result of severe weathering of alluvial deposits by denudation and desiccation, and contains occasional stringers of sub-rounded pebbles, stiff to hard clay lenticels or sand pockets. Although these soil formations can usually provide adequate bearing support to building foundations, their nature and composition present difficulties of both sampling and testing which lead to uncertainties in selecting soil parameters and hence either overly-conservative or unsafe design. A study was thus initiated to review current sampling, testing and design practices, and hence recommend appropriate parameters for determining the bearing capacity and settlement of foundations in these soils. This entailed an assessment of sampling and testing requirements in these soils as well as correlation of field test results such as limit pressures pL and deformation moduli Em from pressure meter tests, standard penetration test (SPT) blow counts N and cone penetration test(CPT) point resistances qc and laboratory test results inter alia, from which appropriate design parameters may be extracted. Also, the results of fully-instrumented pile load tests as well as settlement measurements for shallow foundations in these soils have been compared with analytical predictions based on soil parameters thus determined to verify the proposed correlations.