Predicting of uniaxial compressive strength of some igneous and metamorphic rocks by block punch index and cylindrical punch index tests

Abstract

Uniaxial compressive strength (UCS) of rock materials is a crucial parameter in designing of engineering structures to be constructed in/on rock masses. Although the suggested methods for determination of UCS are well known and required relatively simple procedures, preparation of standard core specimens may not be easy for rock materials of heavily jointed rock and/or thinly stratified rock masses. In order to overcome these difficulties to be encountered during sample preparation, the studies on the alternative equations based on results of simple index tests for predicting of UCS of rock materials have been popular. A linear correlation with conversion factor of 5.1 was suggested in literature for predicting of UCS from block punch index (BPI) considering a wide variety of rock types. In this study, the relations were investigated to be used for predicting of UCS from BPIc and also cylindrical punch index (CPI) based on experimental studies employed on seven different igneous and metamorphic rocks, collected from different locations in Hamedan province, west of Iran. The linear regression analysis showed that the conversion factor between UCS and BPIc was obtained as 5.7 for the tested rocks, which is already higher than the proposed value of 5.1. A conversion factor equal to 7.4 was derived for relation between UCS and CPI. In addition, the prediction performance of some well-known equations on the test results obtained in this study for determination of UCS from BPIc, and also CPI were evaluated. Moreover, the coefficients of determination of logarithmic and power functions were higher than any other functions for UCS–BPIc and UCS-CPI relations, respectively.