Coupled effects of compaction conditions and suction on the cyclic behaviour of an unsaturated soil

Abstract

Compaction conditions, including compaction density and water content, can greatly affect the microstructure and macro-behaviour of soils. So far, the effects of compaction conditions on the cyclic behaviour of unsaturated soils at various suctions have not yet been investigated, which is important for many issues (e.g. ground subsidence and road collapse) in engineering geology. In this study, loess specimens were compacted at two dry densities and two water contents. For each compaction condition, three different specimens were prepared and the subjected to different suctions (0, 10, and 30 kPa), followed by cyclic loading–unloading. At the same density and suction, permanent vertical strain increases and resilient modulus decreases as compaction water content increases. This is because the soil skeleton becomes softer due to the existence of extra-large inter-clod pores, as revealed by microstructural analysis. In addition, as dry density increases, a significant reduction in permanent vertical strain and an increase in resilient modulus are observed. The effects of compaction water content and dry density become less significant as suction increases, possibly because the soil skeletons of specimens compacted at higher water contents and lower densities are more sensitive to suction variations. New equations were proposed to describe the influence of compaction conditions on cyclic behaviour, and their performances were examined using data from both the present study and the literature.