Correlation Between Schmidt Hardness and Uniaxial Compressive Strength of Breccia in Kebobutak Formation at Bener Diversion Tunnel, Purworejo, Central Java, Indonesia

This study presents an empirical relationship between Schmidt Rebound Number (N) and Uniaxial Compressive Strength (UCS) of Breccia in Kebobutak Formation at Bener Diversion Tunnel, Purworejo Regency, Central Java Province, Indonesia. Schmidt rebound hammer is considered as the most effective and easiest approach to determine UCS value. The UCS value is one of the five parameters used to determine the Rock Mass Rating (RMR) in the tunnel. The sampling method was taken from 10 Schmidt rebound hammer and Uniaxial Compressive Strength (UCS) tested samples. The test was carried out on the rock matrix horizontally perpendicular to the vertical face tunnel excavation by 10 strokes in each schmidt rebound hammer test. Empirical correlation is described by UCS = 1,3761(N) + 5,7799. This correlation value can be used as a reference for empirical approach carried out on the volcanic breccia matrix that has dominant plagioclase and has rock density value of 2,89 g/cm3, porosity 10,64%, and water content 7,47% which is relatively close to the sample in this study area.