Abstract
The point load index is a simple, fast, and inexpensive method for determining rock strength and can be applied both in the field and in the laboratory. There are, however, some disadvantages and limitations to the method, and the test results can be affected by the person carrying out the test, the rock characteristics, or the test device. In this study we describe an investigation into how the point load index value is affected by the shape of the conical platens used in the test. Point load index tests were carried out using different devices fitted with conical platens of different spherical radii, and on a modified device which circumvented the limitations/disadvantages. It was seen that the point load index value increased as the platen radius increased, as expected. In the case of testing using non-standard conical platens, an equation is proposed to normalize the point load index value with respect to the standard spherical radius value.
Highlights
The point load index (PLI) is regarded as a valuable index test that gives a good initial indication of the rock strength in rock mechanics
Physical and mechanical properties of rock samples The physical and mechanical properties of the rocks used in this study were determined according to the standards suggested by the ISRM and the Turkish Standards Institute (TSE)
PLI tests on different test devices fitted with conical platens of different spherical radii PLI tests were carried out on different PLI test devices fitted with conical platens with different spherical radius values
Summary
The point load index (PLI) is regarded as a valuable index test that gives a good initial indication of the rock strength in rock mechanics. Many researchers have carried out detailed studies on the PLI test procedure, the effect of different loading configurations, sample size and shape, etc. During these studies, some limitations and errors associated with PLI devices have been identified. The results of studies related to PLI demonstrate how important testing is in determining the strength of rocks, especially if the samples cannot be prepared to the required size for the uniaxial compressive strength (UCS) test In such cases, the PLI test is inevitably used to determine the strength of the rocks
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