The Influence of Testing Procedures on Uniaxial Compressive Strength Prediction of Carbonate Rocks from Equotip Hardness Tester (EHT) and Proposal of a New Testing Methodology: Hybrid Dynamic Hardness (HDH)

Yilmaz N. G.

ROCK MECHANICS AND ROCK ENGINEERING, vol.46, no.1, pp.95-106, 2013 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 46 Issue: 1
  • Publication Date: 2013
  • Doi Number: 10.1007/s00603-012-0261-y
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.95-106
  • Keywords: Equotip hardness tester (EHT), Uniaxial compressive strength (UCS), Rebound hardness, Hybrid dynamic hardness (HDH), Rock properties, Size effect, ISRM SUGGESTED METHOD, SCHMIDT HAMMER
  • Dokuz Eylül University Affiliated: No


The Equotip hardness tester (EHT) is a portable and non-destructive instrument used mainly for the dynamic rebound hardness testing of metals. Although various versions of the 'single impacts' and 'repeated impacts' testing procedures have been employed by different authors for different applications, it is not yet known whether a particular testing procedure is more relevant for a specific application in rock engineering. To be able to contribute to the subject, the present study was carried out to determine the suitability of different rebound testing procedures with this instrument for uniaxial compressive strength (UCS) estimations of some selected carbonate rocks. To achieve this goal, as well as four different existing rebound testing procedures, a newly proposed testing methodology involving the parameter hybrid dynamic hardness (HDH) was also employed. The statistical analyses performed on the experimental data, on the whole, showed that the test procedures which are based on single impacts test procedures outperformed the repeated impacts test procedures in terms of UCS prediction accuracy. The prediction capability of the newly introduced testing methodology was found to be superior to those of other procedures considered in this work, suggesting that it could be an efficient tool in practice for preliminary estimates of rock strength. The statistical analyses also indicated that, in practical applications of the EHT using different test procedures, it may be possible to predict the UCS more accurately when apparent density data is available. For the range of specimen sizes considered, no clear evidence of size effect was observed in the mean rebound values. The argument raised by some other authors that the EHT might not be a convenient instrument for the dynamic rebound hardness determination of relatively high-porosity rocks was not confirmed in this study.