Engineers Australia

Characterising compacted soil using shear wave velocity and matric suction

Ana Heitor, Buddhima Indraratna and Cholachat Rujikiatkamjorn

Abstract

The manner in which soil compacts governs the practical and reliable criteria in controlling compaction in the field. A nuclear density meter, based on radioactive isotopes, is the method most commonly used for field compaction, and while it performs well for controlling placement, its localised nature is not suitable for deeper fills or for assessing larger surface areas. In those types of conditions, alternative non-destructive methods should be considered. Numerous research studies have focused on the characteristics of compacted soil at its optimum moisture content under saturated conditions, but only a few have evaluated compacted soil under unsaturated conditions using surface wave and shear wave velocity surveys.

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 will compact, 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.