Engineers Australia

Assessment of the post-compaction characteristics of a silty sand

Ana Heitor, Buddhima Indraratna and Cholachat Rujikiatkamjorn

Abstract

Conventional field compaction control methods are effective at the time of placement. However, the discrete nature of these measurements and a limited depth of investigation can render them unsuitable for post-construction compaction quality assessments of deeper fills or larger surface areas. In this situation, classical destructive geotechnical surveys (i.e. boreholes, cone penetration tests) are sought to evaluate the current fill conditions. Nevertheless, these methods often do not provide the required level of information because only certain locations are tested and they have tremendous implications in terms of cost. The use of available non-destructive methodologies, such as shear wave velocity surveys (i.e. SASW, spectral analysis of surface waves or HVSR, horizontal-to-vertical spectral ratio) together with electrical resistivity tomography surveys (e.g. evaluation of water content), offers a valuable alternative to efficiently control compaction over large areas during post-construction stages and locate areas within the existing formations where the soil was not sufficiently compacted.

This study explores the performance of a cost effective method for evaluating the characteristics of compacted fills by measuring the shear wave velocity and matric suction to evaluate the void ratio or dry density of compacted soil. Laboratory studies of compacted specimens were used to evaluate this method and their performance under different isotropic confining pressures. The results showed that the shear wave velocity and matric suction can effectively predict how the soil is compacted, but its success requires field measurements of both shear wave velocity and matric suction. The application of this relationship would enable practitioners to efficiently control compaction over large areas during post-construction stages, and locate areas within the existing formations where the soil was not sufficiently compacted.