Article Dans Une Revue Geophysics Année : 2025

Induced polarization of clay-rich materials - Part 4 : Water content and temperature effects in bentonites

Résumé

Deep Geological Disposals (DGDs)

are widely seen to be the best solution to safely contain high-level radioactive wastes. Compacted bentonite and bentonite-sand mixtures are considered as the most appropriate buffers or sealing materials for access drifts, ramps, and shafts due to their favorable physicochemical and hydro-mechanical properties.

Bentonite-sand mixtures are expected to swell and seal all voids when in contact with water, forming an impermeable barrier to radioactive elements. The parameters that will most affect the hydraulic performance of these seals are their water content, dry density, water salinity and temperature. Monitoring and assessing these parameters are therefore crucial to confirm that the seals safety functions are fulfilled during the life of a DGD. Induced polarization is a non-intrusive geophysical method able to perform this task. However, its underlying physics for bentonite sand mixtures has not been checked. The complex conductivity spectra of 42 compacted bentonite-sand mixtures were measured in the frequency range 1 Hz -45 kHz in order to develop relationships between in-phase and quadrature conductivities versus water content and saturation, pore water conductivity, bentonite-sand ratio (10% to 90%), temperature (10-60°C), and dry density (0.97 to 1.64 g cm -3 ). We observe that conductivity is mostly dominated by surface conductivity associated with the Stern layer coating the surface of smectite, the main component of bentonite. At a given salinity and temperature, the inphase and quadrature conductivities obey power law relationships with water content and saturation. The in-phase and quadrature conductivities depend on temperature according to a classical linear relationship with the same temperature coefficient. A Stern layer-based model is used to explain the dependence of the complex conductivity with water content, dry density, water salinity and temperature. It could be used to interpret induced polarization field data to monitor the efficiency of the seal of DGD facilities.

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irsn-04874895 , version 1 (11-01-2025)

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J. El Alam, A. Revil, P. Dick. Induced polarization of clay-rich materials - Part 4 : Water content and temperature effects in bentonites. Geophysics, 2025, 90 (2), pp.MR39-MR54. ⟨10.1190/geo2024-0110.1⟩. ⟨irsn-04874895⟩
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