The Use of Fracture Mechanics for the Study of the Progressive Failure in Geomaterials

This paper presents some basic concepts of linear and non linear fracture mechanics, with particular attention to some aspects related to hard soils and rocks such as the behaviour of cracks in compression. A non-linear method is presented in particular, which allows to simulate the process zone at the crack tip as a cohesive crack, where shear resistance decays from the peak to the residual value as a function of the relative slip. A numerical methodology is also presented, based on the BEM technique of the Displacement Discontinuity Method. Finally, two examples of application to the study of the progressive failure in geomaterials are presented. The first is the back analysis of the triggering phase of the Ranc rockfall, occurred in the Vercors massif (F) in 2004. A linear elastic analysis allowed to simulate a toppling failure mechanism due to the progressive failure of surveyed rock bridges. The second example is the simulation of the triggering and evolution of the failure surface below a shallow foundation in overconsolidated clay. A shear band propagation is considered through a non-linear approach. On the basis of realistic values of the input parameters, the results confirm the validity of the methodology in reproducing the theoretical failure surface shape.