Analysis of desiccation cracking in compacted soils using computed tomography

Abstract

Desiccation cracking in soils is a critical issue in geotechnical engineering, particularly in arid and semi-arid environments. Although soil shrinkage and cracking have been extensively studied at the laboratory and field scales, the underlying mechanisms of crack initiation and propagation remain insufficiently understood due to the complex thermo-hydro-mechanical interactions involved. This study uses X-ray computed tomography (CT) as a non-invasive technique to visualize and quantify crack formation and soil deformation in compacted clay specimens subjected to drying and wetting cycles. Compacted specimens were prepared on the dry side, at optimum, and on the wet side of the compaction curve, as well as in slurry form, to explore the influence of soil structure on shrinkage and cracking. Ring-shaped specimens were scanned using microCT, and cylindrical specimens with a rough bottom using macroCT to assess crack morphology, propagation patterns, and soil volume changes. Horizontal and vertical cross-sections were analyzed to identify crack orientation, initiation points, and closure behavior upon wetting. Soil structure emerged as a key factor influencing shrinkage behavior and crack development. Dry side specimens exhibited minimal deformation and low cracking, while wet side and slurry specimens experienced significant volume loss and wide crack openings. Crack closure during wetting was partial, with residual flaws promoting re-opening and the formation of additional cracks in subsequent cycles. CT scans also enabled the calculation of void ratio and construction of Soil Shrinkage Curves (SSCs). Results showed that dry side specimens followed S-shaped SSCs, while wet side and slurry specimens exhibited J-shaped curves. The findings highlight the role of compaction, moisture variation, and initial fabric in desiccation cracking and demonstrate the value of CT in investigating unsaturated soil behavior.