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.