Abstract This study investigates the wetting-induced collapse behaviour of a natural lateritic soil from southern Brazil, emphasizing the coupled hydraulic and mechanical effects that govern its instability. A comprehensive experimental program was conducted, combining one-dimensional consolidation, direct shear, and direct simple shear tests on undisturbed specimens, complemented by soil-water retention and microstructural analyses. The soil exhibits a pronounced dual-porosity structure that controls both suction retention and mechanical response. Upon wetting, an abrupt loss of strength and stiffness occurs due to the breakdown of interparticle bonding and suction, followed by structural reorganization and partial recovery of strength. Collapse deformation measured during shearing closely matches that obtained from conventional consolidation tests, confirming that collapse evolves concurrently with shear strain. Microscopic observations revealed structure breakdown and the formation of a denser and more aligned fabric after flooding under shear. The integrated approach adopted in this research enables a direct evaluation of hydro-mechanical transitions from suction-controlled to friction-dominated behaviour under realistic stress paths. The findings highlight the need to incorporate shear-path effects into the experimental assessment and design of foundations and earth structures on collapsible lateritic soils, contributing to a better understanding of wetting-induced instability in tropical environments.
Falcão et al. (Thu,) studied this question.