Hydro-mechanical behaviour of compacted soils with a pronounced natural multi-modal pore structure
Hydro-mechanical behaviour of compacted soils with a pronounced natural multi-modal pore structure
Natural structured soils with multimodal pore systems often show high collapse susceptibility due to interconnected macrostructural pores sustained by suction and weak bonding agents. Although compaction is commonly used to improve their engineering performance, part of the inherited pore hierarchy may persist after densification and continue governing their hydro-mechanical response. This study investigates two natural structured soils: a lateritic residual soil from southern Brazil and a low-density carbonated clayey silt from the Ebro basin in north-eastern Spain.
The soils were tested in natural and compacted conditions using Standard Proctor energy. Additional hydraulic paths were considered by compacting the Brazilian soil on the dry side of optimum conditions and by drying the compacted Spanish soil after compaction. One-dimensional wetting tests were performed to evaluate collapse susceptibility, while water retention curves were used to assess whether the multimodal pore structure persisted after densification.
The results showed that compaction increased dry density and reduced void ratio, producing a clear decrease in wetting-induced collapse strains. However, collapse susceptibility was not fully eliminated. The natural Brazilian soil exhibited collapse strains above 15% under engineering stress levels, whereas dry-side compaction reduced, but did not suppress, collapse deformation. Similarly, the natural Spanish clayey silt showed collapse strains close to 10%, while compaction at optimum conditions almost suppressed collapse. Nevertheless, post-compaction drying partially reactivated collapse susceptibility despite the higher density achieved.
Water retention results for the Brazilian soil revealed a pronounced bimodal response associated with inter- and intra-aggregate pore domains. Although compaction reduced the largest pores, a double-porosity response persisted after drying, especially for dry-side compaction. This indicates that part of the inherited aggregated structure remains active after densification and may be enhanced by shrinkage-induced enlargement of inter-aggregate pores.
Overall, the results show that the behaviour of compacted structured soils cannot be interpreted only in terms of density or void ratio. The persistence of macrostructural pores continues to control collapse and water retention, highlighting the need to consider microstructure and hydraulic stress paths in engineering applications.
Diones Uiliam Barboza; Laura Gonzalez-Blanco; Enrique Romero; W. Y. Y. Gehling; Washington Peres Nunez; Patricia Rodrigues Falcao
International Conference on Advances and Innovations in Soft Soil Engineering (ICAISSE2026)
Multiphysics Behaviour
https://doi.org/10.53243/ICAISSE2026-228