Mechanisms of Distress Associated with Sulfate-Induced Heaving in Lime-Treated Soils

Abstract

Field observations suggest that ettringite-induced swell in lime-treated soils may manifest rapidly after placement and compaction or after months or even years after lime treatment. In either case, forensic investigations have identified the presence of the mineral ettringite in distressed sections. However, the time window between the observation of distress and the subsequent forensic evaluations has left room for doubt as to whether the ettringite caused the observed distress or was formed between the time of the observed distress and the time of the forensic investigation. The study focuses on identifying alternative, probable mechanisms of swelling when sulfate-laden soils are stabilized with lime. The research addresses the hypothesis that swelling in sulfate-bearing fine-grained soils results from one or a combination of three mechanisms: (a) volumetric expansion during ettringite formation, (b) water movement triggered by a high osmotic suction caused by sulfate salts, and (c) the ability of the ettringite mineral to absorb water and contribute to the swelling process. The data validate the conclusion that a synergy of the mechanisms discussed contributes to swelling distress. The study also addresses the impact of matrix strength of the stabilized soil on damage potential.