Evaluation of relative density profiles of sand fill at a reclaimed site

The determination of relative density is an important part of site characterization for reclaimed sand fill. In practice, a direct determination of the relative density profile is not always possible, and very often one has to resort to indirect methods using in situ tests, such as the cone penetration test. The usefulness of the indirect method is strongly affected by the validity of available correlations. This investigation compares relative density profiles of reclaimed sand fill created from a marine sand by two distinctively different placement methods at the Changi East reclamation site in Singapore as obtained using both the direct and indirect methods. For reclaimed fill, the relative density profile is found to be predominantly influenced by the method of sand placement, although the basic characteristics of the sand also have an effect. Existing correlations developed in calibration chamber tests for indirect evaluation of relative density from the cone resistance in silicate sand are found to provide a slight underestimate of the relative density in direct-dumped fill in Changi, mainly because of the high compressibility of the marine sand. On the other hand, inadequate consideration of overconsolidation and variation in particle size from the specific placement process have led to an overestimate of the relative density in hydraulically placed sand fill in Changi using similarly derived correlations.Key words: in situ density, relative density, sand, land reclamation, cone penetration test, sand placement.