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logo LGM DRYING dessiccation Kinetics of drying

Pierre Gerard


Angélique Léonard (ULg)

Frédéric Collin, Robert Charlier (ULg)

The modelling of unsaturated drying deformable materials is a crucial issue in civil engineering. The geomaterials, whether they are natural (rocks or soils) or worked out by man (concrete), can be subjected to gradients of relative humidity or temperature.

Cement based materials are submitted to interactions with ambient atmosphere during very long periods of time, over which the liquid water content is modified. Shrinkage and cracks induced by the desiccation of these materials could influence the durability of engineering structures. The disposal of radioactive waste in deep and weakly permeable geological layers is also influenced by the required ventilation of the underground drifts during the construction and operational phases of the repository. This process could give rise to a desaturation process of the rock around the cavities. A correct numerical prediction of the coupled processes occurring between the rock mass and the surrounding air during the excavation and the operational phase is therefore needed to obtain the pore water pressure distributions near the gallery wall and predict the development of an excavated damage zone around the cavities. Finally, the problems of drought in some regions induce ground movements associated to shrink/swell of soils (particularly in clayey soils). This is a major cause of worry for specialists involved in the field of constructions. All these latter examples of soil-atmosphere interactions emphasize the need of correct flow boundary conditions in order to deduce the capillary pressure distributions into the geomaterials in interaction with the ambient atmosphere.

In this study, the kinetics of drying is first analyzed from an experimental point of view, by the development of original convective drying tests on silt and clay samples, which allows the determination of transfer coefficients characterizing the soil-atmosphere interactions processes.

An unconventional thermo-hydraulic boundary condition in partial saturation has been developed, combining the evaporation with seepage, yielding much better results in the reproduction of the drying kinetics. Numerical results improve the understanding of the moisture transfer mechanisms through the porous medium and the exchanges with the surrounding atmosphere. The modelling of large scale engineering applications is also performed, as for instance the influence of the ventilation of underground cavities drilled for radioactive waste disposal on the convergence and the desaturation of the host rock. These new modelling tools developed are applicable to a wide range of engineering cases where partial saturation in soils and rocks is essential.

  • Gerard P., Léonard A., Masekanya J.-P., Charlier R., Collin F. (2010) Study of soil-atmosphere moisture exchanges through convective drying tests in non-isothermal conditions, International Journal for Numerical and Analytical Methods in Geomechanics. 34(12), 1297-1320.
  • Gerard P., Charlier R., Chambon R., Collin F. (2008) Influence of evaporation and seepage on the convergence of a ventilated cavity, Water Resources Research. 44(5), doi:10.1029/2007WR00650.