Relationships between soil fabric and suction cycles in compacted swelling soils

This study presents the influence of suction variation on the fabric of two clayey soils, using the mercury intrusion porosimetry (MIP) technique on dense and loose remoulded samples. The experimental study focussed on the evolution of the compacted soil fabric, including the macropores, mesopores, and micropores under various hydromechanical conditions.The variation of void ratio of both samples was initially studied during a single wetting and drying cycle. The experimental results confirm the existence of a suction limit between the meso- and macropores (sm/M) as well as the soil “shrinkage limit” suction (sSL). The suction increase between (sm/M) and (sSL) completely eliminated the macropores and produced mesostructural rearrangement. The higher suctions modified the meso- and micropores.The measured soil water retention curves (SWRC) of these two soils compared with the MIP calculations showed a more reasonable agreement for the dense soil with a fewer macropores.Moreover, several wetting and drying cycles were applied to the remoulded samples. The suction cycles produced a cumulative swelling strain for the dense soil while a shrinkage accumulation was observed for the loose samples. The wetting/drying cycles induced an equilibrium stage in which the samples behaved in an elastic way. The analysis of the soil fabric at this elastic equilibrium stage showed that the suction cycles created significant macrostructural modifications and reorganization of the mesopores towards smaller sizes.

Research highlights
► The suction increase eliminated the macropores and produced meso- and microstructural rearrangement.
► The MIP calculations showed a more reasonable agreement for the SWRC of the dense soil with a fewer macropores.
► The suction cycles created significant macrostructural modifications and reorganization of the mesopores towards smaller sizes.