Paper contribution

A robust sampling strategy for UCS using wireline geophysics

Amirreza Shakib; Anton Kepic; Duy Thong Kieu; Mark Bunch; Nigel Cook; Maryam Parsajoo

Proceedings
EUROCK 2026
Pages
479-484
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Determining where to sample a diamond drillcore and estimating how many Unconfined Compression Test (UCS) samples would be needed to obtain accurate data are tasks largely based on qualitative knowledge. ISRM suggests taking a minimum of five samples per domain. Prior research has shown that due to the natural heterogeneity in rock better insights with statistically based estimations are usually needed. This hypothesis was confirmed in a recent study at the former Brukunga Mine site, South Australia. Our study in a hard/crystalline rock geology revealed a wider variation than initially anticipated. The UCS results from 162 samples showed a minimum value of 22.9 MPa, a maximum value of 320.2 MPa, and a CoV of 59%. Continuous full wave sonic (FWS), and density logs were extracted to calculate dynamic elastic modulus (Ed) along the length of a single borehole. Robust statistical methods were used to create a measure of variation of rock elastic modulus. This measure is called Relative Median of Absolute Deviation (RMAD) over a 5 m-long moving window. Gaussian Mixture Modelling identified a threshold of 3% RMAD that separates the geological record exposed in the borehole into mechanically homogeneous and anomalous zones. A sampling strategy was developed by combination of fuzzy c-means clustering domaining on continuous X-ray fluorescence geochemistry data as well as RMAD zones. The outcome of the study is a sampling strategy guided with RMAD that provides a measurable and quantitative means to take samples, based on the mechanical and geological conditions of the sampled medium.

Contributors

Authors

  1. Amirreza Shakib ARC Training Centre for Integrated Operations for Complex Resources, Adelaide University, Australia ORCID 0009-0004-8005-2296
  2. Anton Kepic RoqSense ORCID 0000-0003-2850-7818
  3. Duy Thong Kieu RoqSense
  4. Mark Bunch Adelaide University, Australia
  5. Nigel Cook Adelaide University, Australia
  6. Maryam Parsajoo RoqSense

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References

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