One-dimensional consolidation of lime-treated dredged harbour sediments

Dunkirk marine sediments can be used as an alternative roadbed material, and a full-scale test road using this has been successfully built at Dunkirk harbour in France. In this context, the long-term deformation behaviour of Dunkirk sediments is of crucial importance in the evaluation of roadbed deformation. The standard oedometer tests were carried out to plot the e-logσ′ and e-logt curves, which were used to determine the compression index (Cc), swelling index (Cs) and coefficient of secondary compression Cα during loading and unloading. The effect of lime treatment on primary and secondary compression behaviour was investigated. The soil structure influences greatly the yield consolidation stress σy′, which is increased with lime content. Both σy′–ey (void ratio at σy′) and Cc–Cs relations are analysed. It is observed that σy′ is connected with ey by a power function and Cc/Cs varies between 0.013 and 0.1. Cα remains low at consolidation stress σ′ < σy′ and reaches a peak at σ′ = (1 – 4) σy′ followed by a decrease in Cα. Lime addition induces the peak Cα moving towards a larger consolidation stress of 5σy′. Based on the Cα–lg(t/tp) curves, it is interesting to note that t = 20tp (end-of-primary consolidation time) is suggested as a sufficient consolidation time to study the secondary compression behaviour of marine sediments. The Cα/Cc ratios of various clays including Dunkirk sediments show that Cα/Cc changes mainly in the range of 0.02–0.05. However, the Cα/Cc ratio is different for lime-treated sediments (Cα/Cc* = 0.0164) and untreated sediments (Cα/Cc* = 0.0432). Two separate zones in Cα–Cs* plot are clearly observed for untreated and treated sediments with boundary line of Cα = 0.0433Cs* – 0.0008.