Evaluation of strength anisotropy and empirical models for estimating strength of rock materials with inclined weakness planes using block punch index test

摘要

Yet the difficulties in preparation of the test specimens according to test standards or suggested methods, and provisions for expensive testing equipment and testing durations motivated the investigators to develop simpler and index type test methods for determination of the mechanical properties. One of these tests is the Block Punch Index (BPI) test accepted by ISRM to indirectly estimate the uniaxial compressive strength (UCS). While the highest strength is obtained in vertical direction to weakness planes in rocks, in case of application of the load to discontinuities at any angle different than vertical, same strength values in every direction can not be obtained due to anisotropy. This study aims to investigate the strength anisotropy associated with discontinuity orientation by performing BPI and UCS tests, and to develop some empirical relationships for estimating the BPI and UCS in the strongest direction, and the UCS from the BPI determined at any angle between the loading direction and weakness plane. The experimental results obtained from six rock types fall into the moderate-to-low strength anisotropy classes. The comparison between the observed and predicted UCS values indicated that the prediction performances of the equations developed are quite well.