Paper contribution

New Three-Dimensional Rock Stress Measurement Method in Vertically Downhole

Tatsuya Yokoyama; Kiyotoshi Sakaguchi; Takashi Danjo; Koji Ogawa

Proceedings
EUROCK 2026
Pages
853-858
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

A new three-dimensional rock stress measurement method for vertically downward-drilled boreholes has been developed. The measurement principle is the stress relief method, which involves bonding a 24-element strain gauges to a conical borehole wall and releasing stress through overcoring. This method is termed the Conical Wall Borehole Overcoring (CWBO) method. In this study, a new observation equation was developed. After resolving various issues through laboratory experiments, the method was finalized following field validation tests. This study initially began with sedimentary soft rocks as the measurement target. First, an adhesive capable of reliably bonding to the rock underwater and enabling measurements approximately half a day later was selected. Next, as the laboratory experiments, we created hole walls with the same shape as the actual site on rock block specimens. We conducted strain sensitivity tests under true triaxial loading, overcoring under biaxial stress, and further performed a circumferential pressure sensitivity test on the recovered core to confirm the reliability of this method. Field experiments were conducted on a sedimentary soft rock, incrementally increasing depth to 30m and 100m. After these results, measurement experiments were conducted at a hard rock site with easier measurement conditions and a shallow depth of 15 m. Based on the series of previous studies, the CWBO method was recognized as a sufficiently practical and reliable method for three-dimensional stress measurement in vertically downhole. We will continue to improve the method performance by applying it to measurements such as crustal stress at greater depths.

Contributors

Authors

  1. Tatsuya Yokoyama Fukada Geological Institute, Japan ORCID 0009-0005-8511-7738
  2. Kiyotoshi Sakaguchi Tohoku University, Japan
  3. Takashi Danjo OYO corporation, Japan
  4. Koji Ogawa OYO corporation, Japan

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References

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