Evaluation of simple methods for assessing the uniaxial compressive strength of rock

Published data on 48 different rocks are used to evaluate the correlations between the uniaxial compressive strength (UCS) values and the corresponding results of point load, Schmidt hammer, sound velocity and impact strength tests. The variability of test results for each test and each rock type was evaluated by calculating the coefficient of variation. Using the method of least squares regression, the UCS values were correlated with the other test values. Also, the test methods were evaluated by plotting the estimated values of compressive strength vs. the measured values of compressive strength for each test. The results indicate that the least variability is shown in the impact strength test. So, among the test methods included in this study, the impact strength test is the most reproducible test; but the variability of test results for the other test methods is within acceptable limits for most engineering purposes. Strong linear relations between the point load strength index values and the UCS values were found for the coal measure rocks and the other rocks included in this study. The Schmidt hammer and the sound velocity tests exhibit significant non-linear correlations with the compressive strength of rock. In the sound velocity test, the data points are scattered at higher strength values. There is no clear relation between the impact strength values and the compressive strength values for the coal measure rocks. A weak non-linear correlation was found between the impact strength values and the compressive strength values for the other rocks. All test methods evaluated in this study, except the impact strength, provide reliable estimate of the compressive strength of rock. However, the prediction equations derived by different researchers are dependent on rock types and test conditions, as they are in this study. (C) 2001 Elsevier Science Ltd. All rights reserved.