Soil suction and cracking from the onset to the end of desaturation: micro-scale evidence and model

Tomasz Hueckel (1) , Boleslaw Mielniczuk (2, 3, 4) , Moulay Saïd El Youssoufi (2, 3, 4) , L.B. Hu (5) , Lyesse Laloui (6)

1 Duke University [Durham]
2 MIST - Laboratoire de micromécanique et intégrité des structures
3 LMGC - Laboratoire de Mécanique et Génie Civil
4 PMMG - Physique et Mécanique des Milieux Granulaires
5 Department of Civil and Environmental Engineering [Toledo]
6 EPFL - Ecole Polytechnique Fédérale de Lausanne

A multi-scale, multi-physics sequence of processes is discussed as developing during drying of non-clayey soils. Two variables are believed to be central in drying: suction resulting from the evaporation and effective stress associated with external constraints imposed on drying shrinkage. These two variables are tracked across the scales, both in experiments and simulations. The effective stress is critical as leading eventually to soil drying-cracking. Cracking is a most unwanted development in soil undergoing dewatering. Drying cracks often arise in the apparent absence of external forces. Hence, a tensile eigen-stress pattern resulting from stiff inclusions, or tensile stress produced by reaction forces at the boundary constraints need to be contemplated to reach cracking criteria. An earlier tubular micro-scale model of porous drying medium indicates that transport of water toward evaporating surface during saturation phase induces a high suction. A critical suction value is reached at which water body boundary is penetrated in an unstable manner by air. At the meso-scale such air penetration constitutes a surface imperfection, inducing a total stress concentration near its tip, and in the presence of significant pore suction, a rapid increase in local tensile effective stress and crack propagation. Recent experimental results from a configuration of a cluster of grains provide geometrical data suggesting that an imperfection resulting from of air entry penetrates deep into the granular medium over 4 - 8 radii of the typical pore. Further evolution entails separation of grain clusters by funicular bridge instabilities, and in the last stage formation of two-grain pendular capillary bridges. The final phase is associated with a gradual decrease of the micro-scale suction within these elementary bridges, which eventually evolve into a positive pressure before the bridge rupture.

Domaines: Génie civil

Tomasz Hueckel, Boleslaw Mielniczuk, Moulay Saïd El Youssoufi, L.B. Hu, Lyesse Laloui. Soil suction and cracking from the onset to the end of desaturation: micro-scale evidence and model. International Symposium on Computational Geomechanics COMGEO III, Aug 2013, Cracovie, Poland. pp.371-380. ⟨hal-01102653⟩