Table 2 and Eq. 3 of the original article are reported incorrectly. The correct Table 2 and Eq. 3 are shown.Equation 3: JRC = 60.32 * Z2 - 4.51. Table 2 Summary of core specimens, indicating nature of fracture (natural or artificial), diameter D, length L, approximate fracture area A, whether artificial fractures from Brazilian test were created according to standard (BT-std) (Hatheway 2009) and the number of specimens in each category n. (Table presented.).