The needle penetration index for estimating the physico-mechanical properties of pyroclastic rocks


Journal of the Southern African Institute of Mining and Metallurgy, vol.123, no.9, pp.463-469, 2023 (SCI-Expanded) identifier

  • Publication Type: Article / Article
  • Volume: 123 Issue: 9
  • Publication Date: 2023
  • Doi Number: 10.17159/2411-9717/1433/2023
  • Journal Name: Journal of the Southern African Institute of Mining and Metallurgy
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Aerospace Database, Communication Abstracts, Compendex, Metadex, Directory of Open Access Journals, Civil Engineering Abstracts
  • Page Numbers: pp.463-469
  • Keywords: needle penetration index, pyroclastic rocks, rock properties
  • Hacettepe University Affiliated: Yes


Preparation of suitable core specimens for physico-mechanical testing s not always possible, particularly for soft and clay-bearing rocks. Although several indirect test methods have been proposed to predict the properties of rocks, specimen preparation from soft rocks for some indirect tests is still difficult. For such cases, the needle penetration test has been developed. In this paper we present a study on the predictability of the physico-mechanical properties of pyroclastic rocks from the needle penetration index (NPI). The NPI, uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), density, and porosity tests were performed in the laboratory on specimens from ten different locations in Turkey. Correlations were established between the NPI values and the physico-mechanical properties. Strong correlations were observed between NPI and both UCS and BTS. General correlations were found between NPI and both density and porosity.