STUDY OF THE BEHAVIOUR AT FAILURE OF COMPLEX MATERIALS AT DIFFERENT OBSERVATION SCALE

The natural material resistance is a fundamental property used in the design of civil engineering works. The aim of this study is to evaluate the behaviour at failure of complex materials at different observation scales. A mechanical characterization is then carried out referring to complex materials such as mélanges, bimsoils or bimrocks composed essentially of stone blocks embedded within a less resistant clayey matrix. The mechanical behaviour of these materials is difficult to characterize due to the many difficulties that arise in laboratory evaluations and field investigations. From an engineering point of view, the variability of the mechanical behaviour of these materials is problematic because it creates difficulties in design and construction of engineering works such as excavations, tunnels and slope stabilization. Currently, designers who face geotechnical design in complex formations with block-in-matrix fabric do not have enough data to make their real mechanical behaviour reliable. Consequently, the design practice presents several difficulties due to the absence of certain methods to make reliable the design data relating to the values of resistance, deformability and volumetric blocks proportion (VBP). The research carried out in this thesis is divided into two parts related to the study and deepening of these topics, in order to identify some solutions to the problems explained above. In the first phase of the thesis, in order to analyse the mechanical behaviour of the heterogeneous material of the sample under examination, a laboratory testing campaign was conducted using unconventional methods. To assess the effect of the VBP on the mechanical behaviour, triaxial tests were carried out. Due to the impossibility of creating representative samples of the investigated natural material, it was decided to carry out specimens of reconstituted material containing different VBP and to analyse the differences between their mechanical responses. Laboratory test results showed a significant influence of VBP on resistance, stiffness, and post-peak behaviour of the samples. In the second phase of the thesis, critical aspects related to complex materials were evaluated no longer on a laboratory scale, but on a real scale. In particular, the purpose of this second part, was to estimate how the average tortuousness index varies according to the VBP within a bimslope and to identify a failure zone width, which can be useful to designers in making correct assessments of the technical and economic feasibility of the intervention that is intended to be carried out.