The design of infrastructures in stiff jointed clay formations: A step towards a geological-geotechnical integrated approach

Due to its geological evolution the Mediterranean area is largely characterized by complex and weak formations. These formations make vulnerable and landslide prone many regions of the Mediterranean countries, with the consequence to expose vital infrastructures, as transportation system and lifelines, to unavoidable hazards. Recent developments in the geological field have given a comprehensive description of the processes that have originated these formations as well as the main features of this wide class of materials such as mélanges, hard soils and structurally complex formations. Differently, the translation into engineering terms of many geological aspects is still very limited and the designer is often left alone when he has to conceive a geotechnical design model (GDM) capable of capturing the design situation and the geotechnical properties of complex formations as relevant for design. Considering the operative framework outlined by the draft version of the new European code for geotechnical design (EC7), this paper presents a conceptual approach that can be followed when designing an embedded retaining structures in Stiff Jointed Clay (SJC), a specific sub-group of the complex formations, frequently affected by landslides, where, likewise in rocks, the scale effect strongly influences the selection of the representative ground properties. In particular, based on a prototype numerical model of a SJC formation implemented for one system of discontinuities, the paper will show the close relationship between the geometrical arrangement of the discontinuities, the geometry of the potential collapse mechanisms and the operational strengths to be used in the calculation models. The data from monitoring of a real case study are promising in the appropriateness of the proposed approach, despite the simplicity of the conceptual and calculation models adopted.