PSI - Issue 32

6

Ivan Pankov et al. / Procedia Structural Integrity 32 (2021) 166–172 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

171

The applicability of the developed criterion has been assessed by comparing the theoretical dependences with the experimental data obtained during tests on Carrara marble samples by Karman and Becker (Fig. 3a), and during tests on Westerly granite by Mogi (Fig. 3b). As can be seen from the figure, the graphs of the theoretical strength match the experimental data quite well. Some differences are seen in the results obtained by Mogi for the load pattern ʹ ൌ ͳ ൐ ͵ (Fig. 3b). As a whole, the comparative analysis results make it possible to conclude that the developed criterion is applicable to estimate conditions of rocks under true triaxial stress. 5. Conclusions It has been found that it is hard to experimentally determine the strength indicators of rocks under the true triaxial stress due to high labor intensity and high costs of the equipment for such tests. For this reason, it is relevant to develop the strength criteria of rocks in a complex stress condition based on results of simple experimental studies. We propose the rock strength criteria to be based on results of the complex determination of the strength indicators, which include tests for the uniaxial tensile, uniaxial compression and biaxial compression. According to the method of the complex rock strength indicator determination, a general form of the strength criterion has been proposed, allowing for all three components of the principal stresses. As an example, a particular case of the strength criterion has been presented, which has a constant influence of the coefficients under the intermediate and minimum principal stress. The proposed strength criterion, as well as the developed method of finding the rock strength indicators, allows a significant decrease of efforts needed to conduct the experimental studies and an increase of the quality of the geomechanical estimations of conditions of elements used during underground mining in difficult geological conditions. Acknowledgments The study has been conducted with a financial support of Perm Kray and the Russian Foundation for Basic Research within the Scientific Project No. 19-45-590004 and the Basic Scientific Research Program (Project No. 0422-2019-0148-C-01). References Alekseev A.D., Nedodaev N.V., 1982. Limiting state of rocks/Kiev: Nauk. Dumka, 200 p. Arora S., Mishra B., 2015. Investigation of the failure mode of shale rocks in biaxial and triaxial compression tests [J]. International Journal of Rock Mechanics & Mining Sciences, 79: pp. 109 – 123. Beron A.I., Chirkov S.E., 1969. Investigation of the strength of rocks under conditions of triaxial uneven compression. Scientific Community of Mining Institute n.a. A.A. Skochinsky, No. 61, p. 33 - 38. Boker R., 1915. Die Mechanik der bleibenderFormanderung auf KristallinischaufgebautenKorper. Forschungsarbeiten auf dem Gebiefe des Ingenieurwesens. Berlin, H. 175-176. Chang C., Haimson B., 2000. True triaxial strength and deformability of the German Continental Deep Drilling Program (KTB) deep hole amphibolite. J Geophys Res 105: 18999 – 19013. Chen J.T., Feng X.T., 2006. True triaxial testing of rocks under high stress condition. Chin J Rock Mech Eng 25(8): 1537 – 1543. Chirkov S.E., 1976. Strength of rocks at triaxial unequal-component compression. FTPRPI, No. 1, p. 11 - 17. Colmenares L. B., Zoback M. D., 2002. A statistical evaluation of intact rock failure criteria constrained by polyaxial test data for five different rocks [J]. International Journal of Rock Mechanics & Mining Sciences, 39: pp. 695−729. Descamps F., Ramos da Silva M., Schroeder C., Verbrugge J.C., Tshibangu J.P., 2012. Limiting envelopes of a dry porous limestone under true triaxial stress states. Int J Rock Mech Min 56: 88 – 99. Filonenko-Borodich M.M., 1961. Mechanical theory of strength/Moscow. Publishing House of Moscow State