Transbaikal State University, Chita, Russia¹ ; Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia²:

V. A. Babello^1,2, Head of laboratory, Professor, Doctor of Engineering Sciences, chita_bva@mail.ru

Stability assessment of exposed rock surfaces during open pit coal mining is currently a topical issue, especially in complex geological and hydrogeological conditions. The authors assess the strength properties of rocks composing a side of Urtui Open Pit Coal Mine. The boundary of the deposit is defined by natural thinning of coal seams and their outcropping under alluvium, and by limiting fractures. Quaternary clay and loam possess the lowest strength. The strength of rocks overlying coal seams and having very heterogeneous composition is low. The highest strength is a feature of coal and rocks below the coal seams, which is explained by their higher density and lower porosity and humidity. Given a long-term influence of moisture on clayey rocks, it is quite possible that they transit from solid condition to plasticity and fluidity, while watering of sandand-gravel deposits can promote suffusion processes in sandy and sandy-loam rocks. The necessity of the stability assessment in some pitwall areas was due to development of unfavorable deformations in pitwall rock mass because of high water content and jointing of rocks lacking any confining layers. In this connection, it is required to ensure reliable input data for geomechanical calculations. The article describes the comparative analysis of data from lab-scale and full-scale tests aimed to determine internal friction angle and cohesion with the collation of the experimentation procedures and equipment. The difficulty of determining rock strength characteristics at a laboratory scale is illustrated. It is also shown that the strength properties found in laboratory and in field differ. An innovative tool for measuring strength of rocks in walls and sides of pits and quarries is described.

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2. ASTM D5731-16. Standard Test Method for Determination of the Point Load Strength Index of Rock and Application to Rock Strength Classifications. Annual Book of ASTM Standards. Vol. 4.08: Soil and Rock (I). West Conshohocken : ASTM International, 2017.
3. Sidorenko A. A., Sirenko Yu. G., Sidorenko S. A. Influence of face advance rate on geomechanical and gas-dynamic processes in longwalls in gassy mines. Eurasian Mining. 2018. No. 1. pp. 3–8.
4. Li-Yun Yang, Chen-Xi Ding. Fracture mechanism due to blast-imposed loading under high static stress conditions. International Journal of Rock Mechanics and Mining Sciences. 2018. Vol. 107. pp. 150–158.
5. Xie Heping, Li Cunbao, Gao Mingzhong, Zhang Ru, Gao Feng et al. Conceptualization and preliminary research on deep in situ rock mechanics. Chinese Journal of Rock Mechanics and Engineering. 2021. Vol. 40, Iss. 2. pp. 217–232.
6. Wen-Jie Xu, Shi Wang, Hai-Yang Zhang, Zong-Liang Zhang. Discrete element modelling of a soil-rock mixture used in an embankment dam. International Journal of Rock Mechanics and Mining Sciences. 2016. Vol. 86. pp. 141–156.
7. Zou P., Zhao X., Meng Z., Li A., Liu Z., Hu W. Sample Rocks Tests and Slope Stability Analysis of a Mine Waste Dump. Advances in Civil Engineering. 2018. Vol. 2018. ID 6835709. DOI: 10.1155/2018/6835709
8. Amarsaikhan T., Shimada H., Wahyudi S., Sasaoka T., Hamanaka A. Optimization of Dump Bench Configuration to Improve Waste Dump Capacity of Narynsukhait Open Pit Coal Mine. International Journal of Geosciences. 2018. Vol. 9, No. 6. pp. 379–396.
9. Paria C. J. B., Pereira E. L., de Lima H. M. Evaluation of the effect of particle size in shear resistance study of an iron mine waste rock pile. Proceedings of the 19^th International Conference on Soil Mechanics and Geotechnical Engineering. Seoul, 2017. Vol. 1. pp. 407–410.
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11. Mirnyy A. Yu. Disperse soils dilatancy studies and the methods of its quantitative assessment. Inzhenernaya geologiya. 2019. Vol. 14, No. 2. pp. 34–43.
12. GOST 12248.1–2020. Soils. Determination of strength parameters by shear strength testing. Moscow : Standartinform, 2020. 20 p.
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16. Babello V. A., Oveshnikov Yu. M., Kurbatov N. E. et al. Device for determining hardness properties of rock formations of pit edges. Patent RF, No. 2239023. Applied: 27.03.2003. Published: 27.10.2004.