Desiccation-induced cracking and its effect on the hydraulic conductivity of clayey soils from Iran

Abstract

Clay materials have many environmental applications, especially in situations where a hydraulic barrier is desired. However, as the plasticity of clay increases, cracks tend to develop during cycles of long dry spells. This is particularly a concern in the construction of covers or installation of landfill liners prior to waste filling. In the present study, specimens prepared from three natural clayey soils from Iran used for clay barrier construction, and one artificial clayey soil, were subjected to cycles of wetting and drying. Surface cracks of different dimensions formed as a result of drying. Specimens with the largest volumetric shrinkage strains typically contained the highest number of cracks. Specimens that developed cracks were subjected to hydraulic conductivity testing. The results showed that the dimension of cracks increased with increasing plasticity index and clay content and, so, the initial hydraulic conductivity increased with increasing plasticity index and cycles of drying and wetting. Cracking increased the hydraulic conductivity by 12-34 times, depending on the plasticity of the soil. After a long saturation time, the hydraulic conductivity of the soils decreased with an increase in saturation time, which could be associated with a self-healing process that affects the soils by different degrees.Résumé : Les matériaux argileux ont plusieurs applications environnementales, spécialement dans des situations où l'on désire une membrane étanche. Cependant, à mesure que la plasticité de l'argile augmente, des fissures ont tendance à se développer durant les cycles de longues périodes de sécheresse. Ceci présente une inquiétude particulièrement pour la construction de couvertures ou de mise en place de membranes étanches avant le dépôt des déchets sur les sites d'enfouissement sanitaire. Dans la présente étude, des spécimens préparés à partir de trois sols argileux naturels d'Iran utilisés pour la construction de membranes argileuses, et un sol argileux artificiel ont été soumis à des cycles de mouillage et séchage. Des fissures de différentes dimensions se sont formées à la surface par suite du séchage. Les spécimens avec les retraits volumétriques les plus importants contenaient typiquement le nombre le plus élevé de fissures. Les spécimens qui ont développé des fissures ont été soumis à des essais de conductivité hydraulique. Les résultats ont montré que la dimension des fissures augmentait avec l'augmentation de l'indice de plasticité et de la teneur en argile, et ainsi, la conductivité hydraulique initiale augmentait avec l'augmentation de l'indice de plasticité et les cycles de séchage et mouillage. La fissuration a augmenté la conductivité de 12 à 34 fois, dépendant de la plasticité du sol. Après une longue période de saturation, la conductivité hydraulique des sols a diminué avec un accroissement de la période de saturation, ce qui pourrait être associé à un processus de cicatrisation qui se produit dans les sols à différents degrés.

Current state of fine mineral tailings treatment: A critical review on theory and practice

“…Desiccation of the topmost fraction occurs relatively quickly and induces the formation of surface cracks due to shrinkage from water evaporation. This results in changes to the material permeability and exposes additional material for drying, though some clay minerals are able to self-repair desiccation cracks when subjected to moisture (Rayhani, et al, 2007). However, material fractions at depths of more than ~0.5 m do not experience significant natural drying even after a prolonged period of time, as demonstrated by Masala and Dhadli (2012).…”

Clay fine fissuring monitoring using miniature geo-electrical resistivity arrays

“…The results from Rayhani et al (2007) showed that the dimension of cracks increased with increasing plasticity index and clay content and so, the initial hydraulic conductivity increased with increasing plasticity index and cycles of drying and wetting. Nahlawi and Kodikara (2006) carried out some experiments on the induced cracking tests on thin layers of clay soils using humidity and temperature controlled chamber for observation, crack initiation and evolution and for moisture content measurement during desiccation.…”

Experiment evidence on the temperature dependence of desiccation cracking behavior of clayey soils

“…Albrecht and Benson (2001) found that the hydraulic conductivity of some clay liner materials caused by desiccation cracks was almost 500 times that of intact soil. The experiments of Boynton and Daniel (1985) and Rayhani et al (2007) showed that soil cracking increases the hydraulic conductivity of several orders of magnitude. In addition, these cracks induced by shrinkage also create weak zones in a soil body with reduced overall mechanical strength and bearing capacity, and increased compressibility.…”