Hydro-mechanical response of crushed argillite and bentonite mixtures as sealing material

Mixture of excavated Callovo-Oxfordian (COx) argillite and MX80 bentonite has been proposed as potential sealing material for the French deep geological disposal facility of radioactive waste. The mixtures hydro-mechanical behaviour was studied in order to assess their response on design requirements. At the as-compacted state, soil fabric analysed by the MIP technique, showed single-modal pore distribution for pure COx and bimodal pore distribution for samples containing MX80. All tested mixtures developed homogeneous behaviour during compaction with no effect of MX80 presence. Swelling potential was evaluated by hydration tests under 4 MPa on highly compacted material (2.0 Mg/m(3)). Swelling increase and saturated permeability reduction was obtained on bentonite content increment. Combining results of the present experimental work and remarks of previous researchers, the characteristic saturation potential slope was determined and exploited to estimate the swelling under 1, 4 and 7 MPa for various COx/MX80 mixtures compacted at different pressures. The experimental verification of the adopted method suggested an approach of identifying possible combinations in terms of compaction and bentonite content that can fulfill design requirements.