Soft peaty clay stabilization in Sri Lanka: Sustainability through utilizing secondary raw materials

In situ deep mixing of soft peaty clay with a binder such as cement can improve strength and compressibility characteristics significantly in a short period of time. However, due to the higher cost and environmental impact of cement as the binder, reducing the cement content using secondary raw materials such as Calcium carbide residue (CCR) and Fly ash (FA) is needed and is focused on this study. Improvements in strength for various proportions of CCR, FA and cement were assessed by conducting unconsolidated undrained triaxial tests for short-term (28 days) and long-term (90 days) curing. Further, behaviour of compressibility was investigated by conducting loading, unloading, and preloading one-dimensional consolidation test on oedometer. Adding only cement has the best improvement while 10% CCR, 15% FA with 5% cement mixture showed the best results among alternative mixtures. The CCR fixation point was 30% and was independent from time. Further, having similar proportions for FA with CCR & cement mixtures provided better results. However, permitting pozzolanic reaction under an overburden stress can noticeably improve the strength & stiffness of peaty clay.