Assessment of brittleness using rock strength and density with punch penetration test

Brittleness fracturing of rock is one of the most popular research areas in rock engineering, since some rocks show brittle fractures under loads. Direct standard testing method for measuring rock brittleness have not available yet. Therefore, rock brittleness is indirectly obtained as a function of rock strength. The aim of this study is not only to introduce direct method to measure rock brittleness as an index via punch penetration test, but also to investigate the relationship between intact rock properties (uniaxial compressive strength, Brazilian tensile strength, and density of rock) and the brittleness measured from the test. To obtain these objectives, rock cores were gathered from 48 tunnel projects throughout the world. Followings the sampling, the samples were prepared and relevant rock tests were carried out to establishment of dataset at the Earth Mechanics Institute of Colorado School of Mines in the USA. Consequently, using generated dataset, new brittleness index (BIm) and rock brittleness classification was introduced base on type, strength and density of rock together with result of punch penetration test. Further, the rock brittleness index was predicted as a function of the uniaxial compressive strength, Brazilian tensile strength and density of rock with correlation coefficient of 0.94.