Experimental Study of Mode I Fracture Toughness Anisotropy in Granitic Rocks

Abstract

Granitic rocks can in general be easily split through three mutually orthogonal surfaces, empirically identified in the field1,2. In this regard, the present study intends to evaluate the mode I fracture toughness of a syenogranite, obtained from a quarry in the city of Cachoeiro de Itapemirim in the state of Espirito Santo. Fracture toughness consists of an intrinsic mechanical property of rocks and indicates the resistance to the initiation or propagation of a fracture as well as the amount of energy the rock absorbs until its fracture. In order to evaluate mode I fracture toughness anisotropy, the Cracked Chevron Notched Brazilian Disc (CCNBD) test was conducted, following ISRM3. Twenty-five (25) samples were tested considering four (4) different orientations: short transverse, arrester, divider and a random direction (inclined). In addition, the indirect tensile strength test (Brazilian test) was also conducted, in order to characterize the samples. The test was performed on fifteen (15) samples and in three (3) different orientations: short transverse, arrester and divider. The tests and sample preparation were carried out at the Structural and Materials Laboratory (LEM-DEC), and the physical properties were obtained at the Geotechnical and Environmental Laboratory (LGMA), both located at PUC-Rio. It is possible to observed that the physical properties results obtained in the present study were very similar to the results obtained by Almeida et al.4 and by Jaques5. In the Brazilian test it was possible to observe that all the mean tensile strength values are similar to each other, which indicates that there is little anisotropy in this rock. In the CCNBD test it was possible to verify that the mean fracture toughness values are similar in every direction, which indicates that there is little anisotropy in this rock as well as in the Brazilian test.