IRS correction incorporation PLT and UCS results The Malmberget case

Authors: Grendas, N; Mawson, M; Thomas, A; Kulcsar, Z; Naumenco, I; Hicklin, C Download Paper

Cite As:
Grendas, N, Mawson, M, Thomas, A, Kulcsar, Z, Naumenco, I & Hicklin, C 2024, 'IRS correction incorporation PLT and UCS results The Malmberget case', in Daniel Johansson & Håkan Schunnesson (eds), MassMin 2024: Proceedings of the International Conference & Exhibition on Mass Mining, Luleå University of Technology, Luleå, pp. 240-250.



Abstract:
Through statistical analysis of the geotechnical database for LKAB Malmberget underground mine using results from point load testing (PLT) and unconfined compressive strength (UCS), the primary objective of this study is to develop a methodology for rectifying field estimated intact rock strength (IRS) data. Collection of IRS data is a crucial step in estimating different advanced rock mass classification systems like RMR89 or IRMR. The study uses 13,700 valid point load tests (out of total 21,000) and 114,000 IRS evaluations within ten different geological units. Apart from a few outliers, UCS results are consistently below 400 MPa. Box plots reveal overlaps in the IRS categories R2 to R6. Comparisons were not possible for IRS categories R0 and R1 in fault zones only, because point load data were absent. The most intriguing discovery was the box area, between the 1st and 2nd quartiles, where IRS logged values correlated with the PLT results. Category R5 box plot corresponded Is50 factor ranges from 4 to 8. For category R6, the Is50 factor spanned from 5 to 8.5, and maximum outliers exceeded an Is50 factor equal to 11 for categories R3-R6. In addition, the study also investigated the role of micro-defects in reducing intact strength.