Influence of reconstitution method on the behaviour of completely decomposed granite

Abstract

Reconstituting soil is common in construction yet the method used can affect the mechanical behaviour of the reconstituted soil when the soil contains a significant amount of fines. A completely decomposed granite was reconstituted following different methods, namely, dry deposition, moist tamping, slurrying and reconstituting after separating fines by washing; then it was tested in compression and shearing. The test results highlight the sensitivity of the soil behaviour to the method of preparation used for reconstitution. It was found that preparation methods involving large amounts of water, such as slurrying (S) or reconstitution after washing the fines (F), can lead to a release of fines, with effect to change the grading and change the mineralogy. Differences between dry-deposited (D)/moist-tamped (MT) specimens and slurried (S)/washed-reconstituted (F) specimens were observed mainly in the volumetric response. Two different normal compression and critical state lines were obtained for the two main methods of preparation (D/MT and S/F). The distance between the normal compression line and critical state line is larger for the S/F specimens than for the D/MT specimens. For residual soils like Hong Kong completely decomposed granite, which contains a significant amount of fines, it therefore seems necessary to understand the potential differences caused by different preparation methods of reconstitution.