Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 24 (a) (b) (c) Figure 6: Typical crack patterns in Alfas cylindrical specimens. (a) Shear plane failure ( D =75 mm); (b) Axial splitting failure ( D =100 mm); (c) Failure on conjugates shear planes ( D =54 mm). (a) (b) Figure 7: The mean curves of (a) Intact rock modulus and (b) Poisson’s ratio of Alfas stone for each of the three diameters in correlation with the uniaxial stress. Mean values of rock properties are plotted against the diameter together with their standard deviation values (Fig. 8). Fig. 8a clearly shows that UCS decreases as the diameter increases for a constant height to diameter ratio. A difference between the UCS for specimens with D =54 mm and D =100 mm is observed, which is up to 11%. Also, the same trend is observed for the strain energy density (Fig. 8d). Fig. 8b and Fig. 8c present the variation of the intact rock modulus and Poisson’s ratio, as derived from the uniaxial compression test using strain gages. Experimental results show that these parameters remain almost constant for different specimen diameters, with mean values of E=13543 MPa and ν=0.234, respectively. The dependence of the lateral and axial peak strains on the diameter of specimens is presented in Fig. 8e and Fig. 8f respectively. The variation of the peak strains is not a monotonic function versus the diameter. A clear maximum exists and corresponds to the specimens with D =75 mm. The high standard deviation values calculated for some experiments series can be attributed to the small number of specimens used for this analysis. Indirect tensile tests The results obtained from the diametral compression tests for the three different circular disc specimen sizes are presented in Tab. 3. Results include values for the splitting tensile strength, the intact rock modulus, Poisson’s ratio and the shear modulus. Note that the intact rock modulus, Poisson’s ratio and shear modulus for each specimen was calculated at 50% of the indirect tensile strength of that specimen. Furthermore, the lateral and axial peak strains up to the peak load were calculated. Note that the intact rock modulus, Poisson’s ratio and shear modulus values calculated for the circular discs with D =54 mm, correspond to only one specimen, because strain gage measurements failed in other specimens of this series.