Moisture effects on damage and failure of Bure claystone under compression

The present work investigates moisture effects on damage and failure properties of Callovo–Oxfordian claystone, the possible host rock for French underground radioactive waste repositories. Claystone specimens of four different moisture levels (dry, 76, 85 and 98%) are tested in constant strain rate compression to characterise their strain–stress relations, damage and failure properties under 12·4 MPa in situ confining stress conditions. The shear and normal stresses on the shearing-induced fracture surface are determined based on the failure modes observed in tests. It is found that both peak and residual strength of the claystone are decreased by the increase in moisture content while its deformability is enhanced. The orientation of compression-induced shearing fracture in the claystone samples is also related to the moisture content. Moreover, more important damage is observed in specimens with higher moisture levels.