Issue 52

C. Caselle et alii, Frattura ed Integrità Strutturale, 52 (2020) 247-255; DOI: 10.3221/IGF-ESIS.52.19 250 Figure 2: a. Axial strain curve of uniaxial test. b. Axial and volumetric strain of triaxial test with confining pressure of 4 MPa c. Axial and volumetric strain of triaxial test with confining pressure of 6 MPa d. Axial and volumetric strain of triaxial test with confining pressure of 8 MPa Sample Confining Pressure [MPa] Peak Deviatoric Stress [MPa] a 0 23.10 b 4 24.72 c 6 25.13 d 8 32.54 Table 1: Results of Peak stress for the uniaxial test ( Sample a) and the three triaxial tests ( Samples b-c-d) Figure 3: Photographic images and schemes of samples at the end of the uniaxial test (a) and of the triaxial tests with confining pressure of 4 MPa (b), 6 MPa a(c) and 8 MPa (d). The clear localization of the failure surface in the sample under uniaxial compression is also observed in the results of DIC analysis (Fig. 5). The map of axial strains (Fig. 5b) describes the additional presence of a sub-horizontal crack that reproduces the shape and orientation of the layering in the rock. A similar evidence was recognized in the macroscopic observation of the sample (Fig. 3a), attesting a good reliability of the DIC results. The failure of weaker layers of the rock, even if manifested