Abstract: The point load intensity index is considered as the optimum method for measuring and estimating uniaxial compressive strength as it is of unique advantage by indirectly determining the uniaxial compressive strength of rock. By summing up a large number of literatures in China and abroad, we found that current research results are limited by the anisotropy of rock materials, fuzzy correspondence of data, heavy equipment and lack of experimental verification. In this paper, we researched the correlation between point load index and uniaxial compressive strength of rock-like isotropic material of different sizes and strengths by using a portable instrument for point load test. According to test results we conclude that the test data follows the normal distribution law with obvious central tendency; size effect of rock-like material on point load index is apparent; according to P-D²_e curve, the highest correlation coefficient is 0.97, indicating that the point load index of irregular samples can be rectified to that of standard equivalent size. Furthermore, the relational expression between point load index and uniaxial compression strength is established, with a correlation coefficient up to 0.994, which suggest that the rectified point load index well reflects the correlation and improves calculation accuracy. Finally, through point load test of irregular specimens, the error of the proposed relational expression is verified within 15%.

Key words: point loading index, uniaxial compressive strength, rock-like material, size effect, statistical method