Effects of Compaction on the Acoustic Velocity in Soils

Abstract

Soil compaction induced by the use of agricultural machinery changes the mechanical and structural properties of soils. Assessment of its effects may be made by acoustic techniques. In this study, a triaxial cell modified to measure the acoustic velocity was used to simulate the compaction process. Unconsolidated‐undrained triaxial tests were performed on two air‐dry remolded soils and one undisturbed field soil taken from sites in Sharkey, Neshoba, and Marshall Counties, Mississippi. Both the deformation and the acoustic behaviors of the soils were studied during a compaction process. It was found that the acoustic velocity and the deviator stress behaved similarly. Both the acoustic velocity and the deviator stress increased linearly at the early stage of compaction and they changed nonlinearly with intermediate compaction. At the extreme case where the soil was compacted to failure, the acoustic velocity and the deviator stress changed only slightly with further compaction. During the unload‐reload cycle, the acoustic velocity and the deviator stress varied steeply and presented hysteretic and load‐history‐dependent properties. Significant influence of water content on both acoustic and deformation behaviors was found. The similarity between the acoustic behavior and the deformation characteristics make the acoustic velocity a promising parameter for monitoring the ongoing compaction process in situ and for long‐term soil survey.