Overconsolidated flysch-type clays. Engineering considerations for the Strait of Gibraltar tunnel project

The stress-strain behaviour of 85 overconsolidated clay samples from Campo de Gibraltar Flysch Through Domain (Algeciras Unit, South Spain) is presented and discussed. The samples were identified and classified following ASTM standards while their chemical and mineralogical composition were determined by chemical and X-ray techniques. Several samples were tested under triaxial as well as oedometric conditions. Given the results, a detailed comparison was made between different theoretical constitutive models and real testing data, using the finite-elements method. The comparison indicated a good fit between experimental data and those found with finite-elements modelling when the Hardening Soil constitutive model was used. This model showed a better fit than did the Modified Cam- Clay model (historically used for modelling clayey soils), although the latter fit proved better for lower strain values (<5%) than higher ones. These results clarify this intermediate material (hard soils – weak rocks) behaviour and will help in Strait of Gibraltar tunnel project design, as these materials are widely involved in this tunnel design.