Brittleness is an important parameter that controls the mechanical behavior and fractures characteristics of rocks in drilling and rock bursting. Lack of accurate evaluation assessing rock brittleness can lead to many risks related to rock mechanics. In this paper, the relationship between brittleness with the ratio of point load index and porosity (PMP), was investigated for Hamedan limestone. Besides, the existing estimation methods for the brittleness index of the rock have been summarized and their application was briefly discussed. In order to estimate brittleness indices and the ratio of point load index to porosity, 18 blocks of Abshineh and Sarab Gyan limestone rocks have been chosen. Abshineh limestone rocks with the Oligo-Miocene age and Sarab Gyan limestones are extracted from Cretaceous rocks. In the following, at first, thin sections of limestone were investigated. Then the physical (porosity (n)) and mechanical properties of limestones were determined. The samples were exposed to point load index (Is 50), uniaxial compressive strength (UCS), and Brazilian tensile strength (BTS) tests, and the ratio of their point load to porosity (PMP) was calculated. Then, the relationship between brittleness indices and PMP (univariate regression) was checked. Also, the relationship between brittleness indices was determined with two-variable regression (input variables including porosity and point load index). Finally, the results of different types of relationships were compared. The results illustrate that using the PMP parameter, to predict the values of brittleness indices, obtains more reliable results compared to two-variable regression (n and Is 50). Also, the results of experiments showed that the highest agreement between brittleness parameters B3 and B4 with PMP parameter and the coefficient of determination (r2) are 0.89 and 0.90, respectively.

Keywords