Far Eastern Federal University, Vladivostok, Russia:

B. G. Tarasov, Professor, Doctor of Engineering Sciences, bgtaras@gmail.com

Brittleness is one of the critical characteristics of rocks as it governs their fracture mode (steady-state or spontaneous) and dynamics, which is very important for the mining practice. This article discusses the brittleness criteria under triaxial and uniaxial compression. A whole series of criteria were proposed for this important characteristics at different time. These criteria include different parameters which are determined experimentally in compression tests of rock samples, for example, elastic, irreversible and total strain at pre- and post-limit strength; elastic and post-limit moduli; values of different type energy (elastic, free and destructive) in pre- and post-limit fracture, etc. This study aims to attract attention of the geomechanical society to the universal brittleness criterion, which, unlike many other criteria, has a rigorous physical substantiation and enables an unambiguous definition of frangibility of rocks under different type compression (uniaxial, biaxial, triaxial) and in any variation range of lateral pressure. It is based on the balance of fracture energy beyond the strength limits and characterizes the ability of rocks to fracture spontaneously, owing to the elastic energy accumulated in the material before the limit strength. The criterion makes it possible to construct a unified scale which unambiguously defines variation of brittleness in a range from absolute brittleness to absolute quasi-plasticity subject to variation in the post-limit modulus. The experimental results described in this article demonstrate a dramatic increase in brittleness of strong rocks under triaxial compression which complies with the depth-related seismicity.

1. Coates D. F., Parsons R. C. Experimental criteria for classification of rock substances. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 1966. Vol. 3, Iss. 3. pp. 181–189.
2. Hucka V., Das B. Brittleness determination of rocks by different methods. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 1974. Vol. 11, Iss. 10. pp. 389–392.
3. Kidybiński A. Bursting liability indices of coal. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 1981. Vol. 18, Iss. 4. pp. 295–304.
4. Petukhov I. M., Linkov A. M. Mechanic of rock bumps and discharges. Moscow : Nedra, 1983. 279 p.
5. Trofimov A. V., Kirkin A. P., Rumyantsev A. E., Yavarov A. V. Use of numerical modelling to determine optimum overc oring parameters in rock stress–strain state analysis. Tsvetnye Metally. 2020. No. 12. pp. 22–27. DOI: 10.17580/tsm.2020.12.03
6. Stavrogin A. N., Protosenya A. G. Mechanics of rock deformation and fracture. Nedra, 1992. 223 p.
7. Andreev G. E. Brittle Failure of Rock Materials: Test Results and Constitutive Models. Rotterdam : A. A. Balkema, 1995. 456 p.
8. He C., Okubo S., Nishimatsu Y. A study of the class II behaviour of rock. Rock Mechanics and Rock Engineering. 1990. Vol. 23, Iss. 4. pp. 261–273.
9. Tarasov B. G. Universal scale of brittleness for rocks failed at compression. Proceedings of the 13^th International Conference of the International Association for Computer Methods and Advances in Geomechanics. Sydney, 2011. Vol. 1. pp. 669–673.
10. Тarasov B., Potvin Y. Universal criteria for rock brittleness estimation under triaxial compression. International Journal of Rock Mechanics & Mining Sciences. 2013. Vol. 59. pp. 57–69.
11. Galchenko Yu. P., Eremenko V. A., Myaskov A. V., Kosyreva M. A. Solution of geoecological problems in underground mining of deep iron ore deposits. Eurasian Mining. 2018. No. 1. pp. 35–40. DOI: 10.17580/em.2018.01.08
12. Eremenko V. A., Lushnikov V. N. Procedure for selecting dynamic ground support for rockbursting mining conditions. GIAB. 2018. No. 12. pp. 5–12.
13. Yingjie Xia, Hui Zhou, Chuanqing Zhang, Shihai He, Yang Gao et al. The evaluation of rock brittleness and its application: a review study. European Journal of Environmental and Civil Engineering. 2019. Vol. 23. DOI: 10.1080/19648189.2019.1655485

14. Fanzhen Meng, Ngai Yuen Wong L., Hui Zhou. Rock brittleness indices and their applications to different fields of rock engineering: A review. Journal of Rock Mechanics and Geotechnical Engineering. 2021. Vol. 13, Iss. 1. pp. 221–247.
15. Zhihao Kuang, Shili Qiu, Shaojun Li, Shihui Du, Yong Huang et al. A New Rock Brittleness Index Based on the Characteristics of Complete Stress–Strain Behaviors. Rock Mechanics and Rock Engineering. 2021. Vol. 54, Iss. 3. pp. 1109–1128.
16. Cook N. G. W. The failure of rock. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 1965. Vol. 2, Iss. 4. pp. 389–403.
17. Tarasov B. G. Post-limit properties and cor relation with spontaneous fracture dynamics in rocks. Gornyi Zhurnal. 2021. No. 1. pp. 13–19. DOI: 10.17580/gzh.2021.01.03
18. Batugin A. S. General features of strong rock bursts and induced earthquakes in critical-stress areas of th e Earth’s crust. Gornyi Zhurnal. 2021. No. 1. pp. 22–26. DOI: 10.17580/gzh.2021.01.04