This paper presents the results of a comprehensive experimental study of the desiccation of fine-grained soils. Air drying of initially saturated soil slabs in controlled conditions is investigated by performing three kinds of tests: free desiccation tests, constrained desiccation tests (prevented shrinkage), and crack pattern tests. Strains, suction, water con- tent, and crack geometry are investigated. Results reveal that unconstrained drying exhibits two stages: a domain with large, mostly irrecoverable deformations and degree of saturation close to 100%, followed by a domain with lower defor- mations at a decreasing degree of saturation. Homogeneous soil macroscopic cracking is possible only in the presence of boundary constraints and (or) moisture gradients, inducing the build-up of tensile stresses. Results also show that, for the initially saturated remoulded soils tested here, in the whole sample and near a crack initiation point, the degree of satura- tion remains very close to 100% until cracking, while cracking onset, the air-entry suction, and the shrinkage limit are close to each other. Cavitation nuclei and the formation of an irregular drying front at cracking initiation are commented upon in light of this observation. Finally, results suggest that the crack pattern geometry is the result of energy redistribu- tion. A quantification of the process is proposed. Resume´ : Cet article presente les resultats d'une etude experimentale complete de la dessiccation de sols fins. Le sechage de sols initialement satures est etudiedans des conditions controlees et atemperature ambiante. Trois types d'essais ont eteeffectues : essais de dessiccation libre, essais de dessiccation avec contraintes (le retrait est empechedans une direc- tion) et essais de plans de fissures. Les deformations, la succion, la teneur en eau et la geometrie des fissures ont eteinves- tiguees. Les resultats demontrent que le sechage sans contrainte presente deux etapes : un domaine durant lequel les deformations sont grandes et irreversibles et le degrede saturation reste pres de 100 %, suivi d'un domaine durant lequel les deformations sont plus faibles et le degrede saturation diminue. Pour un sol homogene, des fissures macroscopiques apparaissent seulement lorsqu'il y a des contraintes aux frontieres et (ou) des gradients d'humidite ´, ce qui induit des contraintes en tension. Les resultats montrent aussi que pour les silts et argiles remanies initialement satures utilises dans cette etude, le degrede saturation reste tres pres de 100 % jusqu'ala fissuration. De plus, la fissuration, l'entree d'air et la limite de retrait sont proches les unes des autres. Suite a ces observations, l'existence de germes de cavitation et la forma- tion d'un front de sechage irregulier lors de l'initiation des fissures sont discutees. Finalement, les resultats suggerent que la geometrie des fissures resulte d'une redistribution de l'energie a travers le corps. Une quantification du processus est proposee. Mots-cles: dessiccation, initiation de fissure, succion, succion a l'entree d'air, geometrie des fissures.

https://people.duke.edu/~hueckel/desiccationpapers/2009.can.fundam of cracking.pdf

Fundamentals of desiccation cracking of fine-grained soils: experimental characterisation and mechanisms identification

Experimental characterization of shrinkage and desiccation cracking in thin clay layer

https://hal-enpc.archives-ouvertes.fr/hal-00629665/document

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https://hal.archives-ouvertes.fr/hal-00539624/document

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Improvement of the crack resistance of clayey soils by fiber reinforcement was investigated using initially saturated and fiber-reinforced soil specimens subjected to desiccation. An image-processi...

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The authors wish to thank the discussers for their interest in the work on crack formation in clays during drying. The model presented by the authors holds for soils with a high clay content in which desiccation cracks form while the soil is still saturated. This was the case for the Saint-Alban clay for which cracks appeared for a suction of about 23 kPa, 18 hours after the soil surface was exposed to evaporation. Only the onset of cracking was modelled, and crack depth is approximated with linear elastic fracture mechanics in mode I, i.e., opening of the crack. Further crack propagation occurs with the ongoing evaporation leading eventually to the formation of secondary and even tertiary cracks if the soil is restrained in all directions. Furthermore, these cracks, depending on soil type, may be initiated in an unsaturated soil. Hence, we agree that the model must then also consider unsaturated soil mechanics. Owing to differential behaviour between a relatively dryer surface layer and soil at a higher moisture content with increasing depth, secondary crack propagation may also be controlled, in some cases, by shear failure at the crack tip. As stated by the discussers, the cracking problem is complex and the subject received little attention so far.

R Ayad

Papers

A idealized framework for the analysis of cohesive soils undergoing desiccation