Scale effects in rock strength properties. Part 2. Point load test and point load strength index

In rock mechanics and engineering geology, the point load test is regarded as a valuable field test to give an estimate of the unconfined compressive strength. Well known is the scale effect concerning the point load strength since the first comprehensive paper by Broch & Franklin (1972). After carrying out a large high number of point load tests in different rock types and with different devices, the result of this contribution is more an examination of evaluation methods of this apparently simple rock test. Since the I, is highly dependent on the sample size, determination of the Iso seems still to be the major problem. In this paper, a size correction method for obtaining point load strength index Iso is presented using logarithmic regression analysis from a series of performed tests.