Studyng the strength properties of weak brittle rocks when testing a point load specimens

Comparative tests of rocks of medium and weak strength using methods of concentrated loading of samples, implementing multifunctional and simplified approaches to determining strength, have been carried out. It was found that within the limits of one lithological type, the influence of rock strength and density on the value of the brittleness coefficient in strength is insignificant. Taking this into account, it is proposed to extend the methods of testing samples with a concentrated load to weak brittle rocks with a tensile strength of less than 0.5 MPa. Studies of the strength properties of rocks of the coal-bearing stratum and bedrock of the Solntsevo brown coal deposit have been performed according to the data of concentrated load tests. The average values of the fragility coefficient of weak brittle rocks of the deposit in a state of natural humidity are determined. It is shown that an increase in the humidity of weak brittle rocks of the deposit causes a decrease in strength and a decrease in their brittleness (a decrease in the fragility coefficient, on average, by 1−1.5). A calculation method has been developed for the transition from strength indicators determined by the Point Load Strength Test to indicators determined by the method of sample destruction using spherical indenters. Two options for the transition methodology are proposed. The first option implements a scheme of improved tests with spherical indenters when replacing the load elements with truncated conical platens with rounded ends. The second, simplified one, uses the data from Point Load Strength Test, which are supplemented with information about the lithological type of rock and use correlation dependencies for averaged parameters. In this case, the use of samples of irregular shape is allowed.

Korshunov V. A., Shokov A. N., Dordziev D. Yu., Cherskikh O. I. Studyng the strength properties of weak brittle rocks when testing a point load specimens. MIAB. Mining Inf. Anal. Bull. 2024;(11−1):97—115. [In Russ]. DOI: 10.25018/0236_1493_2024_111_0_97.

Korshunov V. A., Cand. Sci. (Eng.), Leading Researcher, Empress Catherine II St. Petersburg Mining University, St. Petersburg, Russia, maok@bk.ru, https://orcid. org/0009−0002−6330−0230;
Shokov A. N., Cand. Sci. (Eng.), Leading Senior Researcher, Empress Catherine II St. Petersburg Mining University, St. Petersburg, Russia, ntl2000@yandex.ru;
Dordziev D. Yu., Cand. Sci. (Eng.), Head of geomechanical service, “East Mining Company” LLC, Moscow, Russia, dordzhievd@eastmining.ru;
Cherskikh O. I., Cand. Sci. (Eng.), Director, “Solntsevsky coal mine” LLC, Shakhtersk, Russia;

Korshunov V. A., e-mail: maok@bk.ru.

1. Barton N., Shen B. Risk of shear failure and extensional failure around over-stressed excavations in brittle rock. Journal of Rock Mechanics and Geotechnical Engineering. 2017. Vol. 9, Iss. 2. pp. 210–225.

2. Ismail M. K. A., Mohd-Nordin M. M., Hasan A. S. Md., Albar A., Razali M. N. Shear strength behaviour of rock joint material influenced by different weathering grade. Journal of Physics: Conference Series. 2019. Vol. 1349. Iss. 1. N 012069. DOI: 10.1088/1742−659 6/1349/1/012069.

3. The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007–2014. International Society for Rock Mechanics, Ulusay R. (editor). Springer International Publishing Switzerland. 2015. DOI 10.1007/978−3-319−07713−0.

4. Kartashov Yu. M., Matveev B. V., Mikheev G. V., Fadeev A. B. Durability and deformability of rocks. Moscow: Nedra, 1979, 269 p. [In Russ].

5. GrishchenkoА. I., SemenovА. S., Melnikov B. Е. Modeling the processes of deformation and destruction of the rock sample during its extractionfrom great depths. Journal of Mining Institute. 2021. Vol. 248, pp. 243–252. [In Russ]. DOI:10.31897/PMI.2021.2.8.

6. Li Y., Oh J., Mitra R., Canbulat I. A Fractal Model for the Shear Behaviour of LargeScale Opened Rock Joints. Rock Mechanics and Rock Engineering. 2017. Vol. 50. Iss. 1, pp. 67–79. DOI: 10.1007/s00603−016−1088−8.

7. Akram Deiminiat, Li Li, Feitao Zeng, Pabst T., Chiasson P., Chapuis R. Determination of the Shear Strength of Rockfill from Small-Scale Laboratory Shear Tests: A Critical Review. Hindawi Advances in Civil Engineering. 2020. Vol. 2020. ID 8890237. DOI: 10.1155/2020/8890237.

8. Molina S. L., Bradfield L., Fityus S. G., Simmons J. V., Lizcano A. Design of a 720-mm Square Direct Shear Box and Investigation of the Impact of Boundary Conditions on LargeScale Measured Strength. Geotechnical Testing Journal. 2020. Vol. 43. Iss. 6. DOI: 10.1520/ GTJ20190344.

9. Protosenya A. G., Iovlev G. А. Prediction of spatial stress-strain behavior of physically nonlinear soil mass in tunnel face area. Mining Informational and Analytical Bulletin. 2020. No 5, p. 128–139 [In Russ]. DOI: 10.25018/0236−1493−2020−5-0−128−139.

10. Nguyen Tai Tien, Karasev M. A., Vilner M. A. Study of the stress-strain state in the subrectangular tunnel. Geotechnics for Sustainable Infrastructure Development: Conference Proceedings. Series: Lecture Notes in Civil Engineering. Singapore: Springer, 2020. Vol. 62. pp. 383–388.

11. Gospodarikov A. P., Trofimov A. V., Kirkin A. P. Evaluation of deformation characteristics of brittle rocks beyond the limit of strength in the mode of uniaxial servohydraulic loading. Journal of Mining Institute. 2022. Vol. 256. pp. 539–548.[In Russ]. DOI:10.31897/PMI.2021.2.8.

12. Kozyrev A. A., Kuznecov N. N., Makarov A. B. On criteria of rock burst hazard. Russian Mining Industry. 2023; (1 Suppl.):00–00. [In Russ]. https://doi.org/10.30686/1609−9192−2023-S1−00−00.

13. Noskov V. A., Tsirel S. V., Korchak P. A. Investigation of the impact of geodynamic risk on the financial and economic activities of mining enterprises, Rock Mechanics for Natural Resources and Infrastructure Development — Proceedings of the 14th International Congress on Rock Mechanics and Rock Engineering, ISRM 2019, 2020, С. 330–335.

14. Trushko V. L., Protosenya A. G., Ochkurov V. I. Prediction of the geomechanically safe parameters of the stopes during the rich iron ores development under the complex mining and geological conditions // International Journal of Applied Engineering Research. 2016. Vol. 11. Iss. 22. pp. 11095−11103.

15. Zhabko A. V. Underlying problems of practical geomechanics and possible ways to overcome them. News of the Ural State Mining University. 2018. Iss. 4(52), pp. 98–107. [In Russ]. doi.org/10/21440/2307−2091−2018−4-98−107.

16. Franklin J. A. Suggested Methods for Determining Points Load Strength // International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 1985. Vol. 22. Iss. 2. Pp. 51–60. DOI: 10.1016/0148−9062(85)92327−7.

17. Kong F., Shang J. A Validation Study for the Estimation of Uniaxial Compressive Strength Based on Index Tests. Rock Mechanics and Rock Engineering. 2018. Vol. 51 (7). 2289–2297. doi.org/ 10.1007/s00603−018−1462−9.

18. Bieniawski Z. T. Estimating the strength of rock materials. Journal of the South African Institute of Mining and Metallurgy. 1974. Vol. 74. Nо 8, pp. 312−320.

19. Ilinov M. D., Korshunov V. A., Pospekhov G. B., Shokov A. N. Integrated experimental research of mechanical properties of rocks: Problems and solutions. Gornyi zhurnal, 2023, No 5, pp. 11–18. [In Russ]. DOI: 10.17580/gzh.2023.05.02.

20. Wang M., Zhang C., Xu W. Study on the mechanical properties of anisotropic red sandstone under point load strength test and uniaxial compression strength. Journal of Civil Engineering and Environmental Sciences 2023. 9(2): 025−032. DOI: 10.17352/2455−488X.000064.

21. Sahin M., Ulusay C., Karaki H. Point load Strength Index of Half-Cut Core Specimens and Correlation with Uniaxial Compressive Strength. Journal of Rock Mechanics and Rock Engineering, April 2020. 53 (8), 3745−3760. doi.org/10.1007/s00603−020−02137−9.

22. Zhao R., Tao M., Cao W. Strength and failure characteristics of marble spheres subjected to paired point loads. Journal of Rock Mechanics and Geotechnical Engineering, September 2023. 15 (9). 2282−2290. doi.org / 10.1016/ jrmge.2022.11.019.

23. Ilinov M. D., Petrov D .N., Kolonaevsky E. V., Straupnik I. A. Usability of acrilates in damp proofing in deep-level salt mining. Gornyi Zurnal. 2023. No 8, pp. 77–87. [In Russ]. DOI: 10.17580/gzh.2023.08.10

24. Dashko R. E., Lokhmatikov G. A. The Upper Kotlin clays of the SaintPetersburg region asa foundation and medium for unique facilities: an engineering-geological and geotechnical analysis. Journal of Mining Institute. 2022. Vol. 254, pp.180–190. [In Russ]. DOI:10.31897/PMI.2022.13

25. Kolapo P., Munemo P. Investigation the correlations between point load strength index, uniaxial compressive strength and Brazilian tensile strength of sandstones. A case study of QwaQwa sandstone deposit. International Journal of Mining Engineering, 2021. Vol. 12, No. 1, pp. 67–83. DOI: 10.1504/IJMME. 2021. 114915.

26 Singh H. K., Basu A. Evaluation of existing criteria in estimating shear strength of natural rock discontinuities. Engineering Geology. 2018. Vol. 232. pp. 171–181.

27. Hoek E. Rock Mechanics Laboratory Testing in the Context of a Consulting Engineering Organization. Int. J. Rock Mech. Min. Sci. and Geotech. Abstract 14 (1977), pp. 93–101.

28. Ovalle C., Linero S., Dano C., Bard E.,Hicher P.-Y., Osses R. Data Compilation from Large Drained Compression Triaxial Tests on Coarse Crushable Rockfill materials. Journal of Geotechnical and Geoenvironmental Engineering. 2020. Vol. 146, Iss. 9. 06020013. DOI: 10.1061/(ASCE)GT.1943−5606.0002314.

29. Zuev B. Yu., Istomin R. S., Obozhina E. P. Physical simulation of nonlinear geomechanical processes in potash ore mining. Gornyi zhurnal, 2023, No 5, pp. 75–80. [In Russ]. DOI: 10.17580/gzh.2023.05.11.

30. Stigsson M., Mas Ivars D. A Novel Conceptual Approach to Objectively Determine JRC Using Fractal Dimension and Asperity Distribution of Mapped Fracture Traces. Rock Mechanics and Rock Engineering. 2019. Vol. 52, pp. 1041–1054. DOI: 10.1007/ s00603−018−1651−6.

31. Kohno M., Maeda H. Correlation between Point Load Strength Index and Physical Properties of Hydrothermally Altered Rocks. International Journal of Mining Engineering and Mineral Processing, 2018; 7(1): 1−13 doi: 10.5923/j.mining 2018 070.01.

32. Alitalesh M., Mollaali M., Yazdani M. Correlation between uniaxial strength and point load index of rocks. Japanese Geotechnical Special Publication. January 2016, 2(12): pp. 504–507. DOI: 10.3208/jgssp.IRN-08.

33. Endait M., Juneja A. New correlations between uniaxial compressive strength and point load strength of basalt. International Journal of Geotechnical Engineering. 2015. Vol. 9, pp. 348–353 doi:.org/ 10.1179/1939787914Y.0000000073.

34. Zingano A. C. Estimating Coal Strength Based on Historical Laboratory Tests and Geomechanics Classification. Aspects Min. Miner. Sci. 5(4). 2020. pp. 620–625. DOI: 10.31031/ AMMS: 2020.05.000618.

35. Yakubovskiy M. M., Mikhailova E. A., Mikhailova E. A., Bazhukov A. A. Reasons of efficiency of surface miners in selective coal cutting under low temperatures. MIAB. Mining Inf. Anal. Bull. 2021;(10):42−57. [In Russ]. DOI: 10.25018/0236_1493_2021_10_0_42.