Reliability and evaluation of point load index values obtained from different testing devices

In some rock mass classification methods, the point load index (PLI) value is used as a parameter in the determination of the class of rock mass. The PLI value may be used as a design parameter such as uniaxial compressive strength (UCS) and tensile strength (TS), owing to its being simpler, faster, and cheaper and easier to prepare than the specimens for UCS and TS tests. It can also be carried out in both the field and the laboratory. Many researchers have investigated PLI testing and the effect of different loading configurations, sample size, and size correction factors. Within the scope of this study, PLI tests were performed in 15 different point load index testing devices. The experiments were carried out on seven different rock types (three sedimentary, one metamorphic, three magmatic) by the same operator. The errors of the testing devices were investigated based on the experimental results, and a device was modified to avoid the errors identified. Additional experiments were carried out in the modified testing device to acquire more realistic values. The PLI values obtained from the modified device were found to be more reliable, with standard deviations lower than those obtained from other conventional testing devices.