Point Load Strength Index and Uniaxial Compressive Strength

Point Load Strength Index (I-g(50)) and Uniaxial Compressive Strength ( sigma(c) ) are evaluated for different Indian rocks, and attempt is made to find correlation, if any, between the two. The rock types studied include - Quartz Mica Schist from six different locations, Quartz Biotite Schist, Gneissose Schist, Amphibolite, Augen Gneiss and Biotite Gneiss. In five out of the above twelve cases, I-g(50) and sigma(c) are evaluated in both, dry and saturated, states. On the basis of recommended values for I-g(50) and sigma(c) for each rock type from a given location, in a given state, i.e. dry or saturated, the correlation factor, k, is established as a ratio of the latter to the former. The major findings are - k can differ even for the same rock type from two different locations; k for a given rock type from a given location, in dry and saturated states need not be same; k can be even outside the range of 15 to 50 given in literature; and the spread or distribution of I-g(50) and sigma(c) is dissimilar in most cases. These findings imply that extreme caution needs to be exercised in evaluating sigma(c) on the basis of 22 times I-g(50) as suggested in literature.