A new index for evaluation of rock brittleness

In the recent decades, the study of rock brittleness in infrastructure projects were addressed by different researchers. Unfortunately, up to now, a universally accepted definition for rock brittleness had not been presented. Furthermore, due to lack of equipment as well as complexity and time consuming of the preparation and testing procedures in the proposed methods of direct measuring of rock brittleness, most of researches were carried out on the basis of indirect indices. Suggested brittleness Indices can be categorized according to the parameters which were used in developing these indices. One of the most important Brittleness Indices which has been widely used in various rock mechanic project is strength based brittleness index. The main objective of this study is to provide a new index based on uniaxial compressive and tensile strength for evaluating the rock brittleness. For this purpose, firstly, by reviewing the existing strength based indices for evaluating rock brittleness, a general equation was suggested for the new index. Then, by using statistical and probabilistic analysis on the obtained results for rock brittleness in punch penetration test, the coefficients of suggested index were calculated. According to the results, the values of 0.807 and 0.4458 were proposed for uniaxial compressive strength and tensile strength coefficients, respectively. Using the suggested index, it is possible to predict the rock brittleness with the value of R2 equal to 0.878.