The Effect of Mineral Composition on the Correlation between Point Load Index with the Uniaxial Compressive Strength of Sulfate Rocks and their Point Loading Deformation

Abstract

Point load test is a common, inexpensive and fast test for the indirect achievement of compressive or tensile strength of the rocks in the laboratory and the field. In this research, by conducting uniaxial compression test (UCT), axial (APLT), and diametral (DPLT) point load tests on gathered sulfate rock blocks from the Gachsaran Formation outcrops at the four under-construction reservoir dam sites in Iran, investigate the effect of mineral composition on the relationships between point load index, the uniaxial compressive strength (UCS) and their point load deformation. Regarding that, firstly by creating a correlation between axial (APLI) and diametral (DPLI) point load index and UCS, relationships for each specific mineral composition were provided. Secondly, by comparing the reliability of the APLT and DPLT results in predicting UCS, the conversion factors of the APLI and DPLI to the UCS were calculated. Thirdly, the effect of unique or multiple sampling locations in the analysis results was compared, and finally, for the first time, the deformation of loading points in point load tests was investigated. The results of this study confirmed that by variation of mineral composition of sulfate rocks, the relationships between APLI and DPLI, and UCS, conversion factors as well as loading points deformation patterns during point load tests are changed significantly, and the results of APLT and DPLT can be used to predict UCS with the same reliability in dry and saturated conditions.