Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 29 This issue requires a long discussion which is outside the scope of this paper. For comparison, the obtained Alfas stone UCS data were plotted on the diagram published by Hoek and Brown [28] as shown in Fig. 12. Although the range of specimen diameters does not cover a very wide range, the selected core diameters represent typical core sizes using in geotechnical testing practice. Figure 12: Relationship between UCS and specimen size plotted as dimensionless values [28]. The values of UCS for the Alfas stone that were determined experimentally, are in full agreement with the following formula published by Hoek and Brown [28]:          0.18 50 50 c D (4) where σ c is the calculated UCS measured on the specimen and σ 50 is the calculated UCS of a 50 mm diameter specimen. Furthermore, Kaklis and Vardoulakis [21] suggest that for Dionysos marble the dependence of the splitting tensile strength to specimen size, seems to follow Carpinteri’s fractal law [29] which advocates the formation of a fractal fracture manifold. By observing typical crack patterns generated during specimen failure in the current investigation (see examples in Fig. 6) it is evident that specimen spalling and axial splitting rather than specimen shearing may be the predominant failure modes for the Alfas stone. Both axial splitting and spalling failure modes are related to indirect tensile failure. Fig. 13 presents the variation of the uniaxial compressive strength with the specimen diameter of Alfas stone in a double logarithmic plot. The correlation coefficient of the trend line presented in Fig. 13 is almost 100% which suggests that a similar fractal law may apply for uniaxial compression, when splitting can be considered a predominant failure mechanism. The exponent ݊ in the scaling law for the case of Alfas stone is  2.668 n , based on the procedure detailed in [21]. A similar correlation for the Brazilian tests is not attempted since the variation of the indirect tensile strength with specimen diameter exhibits a non-monotonic behavior. C ONCLUSIONS his paper presents experimental results and correlations on the mechanical behavior of the Alfas stone for a range of uniaxial compression and indirect tension tests. A total of 18 cylindrical specimens and 21 Brazilian disc specimens were tested for three different diameters ( D =54, 75 and 100 mm). Many specimens where fully instrumented with strain gages to fully capture the deformational characteristics of each test. In addition, the dependence of the mechanical parameters on the size of the specimens was investigated. T