Abstract

Clayey soils are very distributed in the region of Beja in the Northwest of Tunisia. These soils are subjected to wetting-drying (W-D) cycles, result a variation in microstructure, macrostructure, and saturated permeability. The desiccations cracks grows during cycles, and the compacted clayey soil show an anisotropic behavior, which was the most important cause of ground fissures, collapse and landslides.

Special tools with large-scale apparatus are important for measuring the vertical and horizontal permeability (Kv and Kh) during W-D cycles for compacted samples with different initial density. Then, a new permeameter was developed to analyze the permeability anisotropy during 6 wetting-drying cycles and to investigate the influence of microstructural, macro-structural in the hydraulic anisotropy. The saturated permeability is assumed to be isotropic (Kh=kv) before desiccation, however, this assumption is invalid during 6 wetting-drying cycles and the pore connectivity of desiccation cracks and permeability in the vertical direction outweighs the horizontal one.

Introduction

Induced by W-D cycles, the region of the north of Tunisia, which is fragile, leads to landslides. The micro and macro-structure varied and the soil is influenced by physico-chemical effect (Louati et al., 2018), then the saturated permeability changed during wetting-drying cycles, which leads to natural hazards. In fact, the evolution of saturated permeability is related to the variation of desiccation cracks during cycles.

The saturated permeability is assumed to be isotropic in recent study; however, the permeability is anisotropic during wetting-drying cycles (Romero et al., 2008; Attom et al., 2008). Then, for describe the saturated permeability, it is necessary to understand the variation of hydraulic anisotropy. However, the anisotropy in the saturated permeability during wetting –drying cycles has not been well explored.

The desiccation cracks provide many preferential pathways for the infiltration of water, then the saturated vertical permeability increase (Rayhani et al., 2008; Li and Zhang, 2010). The cracks networks will be vertical, and extend from the surface downwards. Also, we can observe a horizontal cracks in soil which can contribute to horizontal infiltration (Novak et al., 2000). Water can enter cracks directly from rainfall (Romkens and Prasad, 2006; Greve et al., 2010). The problem of hydraulic anisotropy warrants close attention.

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