Effect of chemical additives on the consolidation behaviours of mini-PVD unit cells –from macro to micro

The mechanism of adding NaCl, CaCl2 and small amounts of cement/lime (1–4% by dry weight) into clay slurry for mitigating the effect of apparent clogging around PVDs during vacuum consolidation was investigated by mini-PVD unit cell consolidation tests as well as microstructure observations via scanning electron microscopy (SEM) imaging. The consolidation test results indicated that for the specimens with CaCl2, cement and lime additives the rate of consolidation increased considerably, while the effect of the NaCl additive was limited. The SEM images show that for the specimen without additive, there were obvious localized deformation-induced microstructure anisotropies. For specimens with CaCl2 and cement/lime additives, the microstructures of the soils tended to be isotropic. The additives tested reduced the thickness of the diffusive double layer around the clay particles and promoted the formation of a more stable flocculated microstructure, therefore mitigating the effect of apparent clogging. •The results of mini-PVD unit cell consolidation test clearly demonstrate that Ca2+ increased the rate of the consolidation.•SEM images provide direct evidence of localized clay particle reorientations, which is a mechanisms of apparent clogging.•The chemical additives can mitigate apparent clogging effect throughpromoting formation of flocculated microstructures.