The influence of initial structure on the evolution of permeability functions of a lean clay for a wide range of void ratios

Although the effect of microstructure on clayey soil permeability is known, the evolution of the permeability–void ratio function for different initial microstructures remains unclear. A developed low-compliance permeameter with a triaxial double-cell and twin-wall burettes was used to investigate the permeability evolution of a lean clay prepared in three distinct initial microstructures at the same void ratio. Eighteen permeability tests revealed the steepest slope of the permeability–void ratio curve for the sample prepared at the slightly wet side of w opt (optimum water content) with the largest aggregation and macro-pores. The other two samples prepared at the two extreme sides of w opt showed permeability functions with a gentler slope, and the reconstituted sample exhibited the lowest permeability function across the tested void ratio range. Observations were supported by microstructural analyses of 10 samples using scanning electron microscopy and micro-computed tomography scan tests. The slightly wet-side sample showed larger ped sizes, higher macro-porosity, and a softer response to compression, while the extreme dry-side sample exhibited a crossover in permeability function due to a more uniform particle clustering and stiffer structure. These results provide useful guidance for selecting compaction conditions to control permeability such as dams and landfill liners.