Multi-scale Assessment of Wetting-Induced Collapse in a Lateritic Soil: From Microstructure to Foundation Performance

Abstract Collapsible soils are a significant concern in geotechnical engineering due to their tendency to undergo volumetric collapse and strength loss upon wetting, which can compromise the performance of foundations and earth structures. Lateritic soils, common in tropical regions, are susceptible to collapse due to their open structure and cementation by sesquioxides. This study evaluates the effects of flooding on the mechanical behavior of a lateritic soil from southern Brazil through an integrated experimental program. The soil exhibited an initial degree of saturation of 63.39%, and the measured matric suction ranged from approximately 3.3 kPa to 30 MPa. Collapse potential measured in oedometer tests increased from 7.1% at 100 kPa to nearly 19% at 1600 kPa. Direct simple shear tests revealed a reduction of up to 74% in apparent cohesion under flooding, with minor changes in friction angle. Physical-model plate load tests showed reductions greater than 60% in ultimate bearing capacity after 48 h of inundation, associated with an estimated 20 kPa decrease in matric suction. Scanning electron microscopy confirmed the breakdown of aggregate bonds and a reduction in microporosity after saturation. The results provide multi-scale evidence that the collapse behavior of lateritic soils is strongly governed by suction-controlled mechanisms, highlighting the critical influence of matric suction on strength and foundation performance.