Brittleness evaluation method based on pre-peak crack initiation and post-peak characteristics of rock
GAO Mei-ben1,2, LI Tian-bin2, CHEN Guo-qing2, MENG Lu-bo2, MA Chun-chi2, ZHANG Yan2, YIN Hong-yu2, ZHONG Yu-yi2
1. School of Emergency Science, Xihua University, Chengdu 610039, China; 2. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China
Abstract:The existing researches show that the brittleness of rock is closely related to the initiation and propagation of internal microcracks, but there are few brittleness evaluation indexes considering the characteristics of rock initiation. Based on the theoretical analysis of brittleness and the characteristics of rock initiation, a brittleness evaluation method is proposed based on the pre-peak initiation and post-peak characteristics of rocks. Firstly, based on the descriptions and definitions of brittleness by George, Tarasov & Potvin et al., the feasibility of evaluation method based on the pre-peak crack initiation and post-peak characteristic brittleness is theoretically analyzed. Secondly, component Bi representing pre-peak brittleness of rocks and component Bii representing the post-peak brittleness of rocks are constructed, and the product of the two is the brittleness index BI representing the pre-peak fracture initiation and post-peak stress drop. Finally, it is verified based on the test data of granite, sandstone and marble under different loading methods, confining pressures and lithology conditions. The results show that the brittleness of marble decreases with the increase of confining pressure from 5 to 35 MPa. At confining pressure of 5 MPa, the brittleness of granite under the triaxial unloading tests is greater than that under the triaxial compression tests. The values of the corresponding brittleness index BI of granite, sandstone and marble are 0.684, 0.336 and 0.186 respectively, and the calculated results are consistent with the experimental ones. This study provides a new way to evaluate the rock brittleness from the perspective of crack initiation and stress drop, which has guiding significance to enrich the analysis and evaluation of indoor rock brittleness.
[1] 李庆辉, 陈勉, 金衍, 等. 页岩脆性的室内评价方法及改进[J]. 岩石力学与工程学报, 2012, 31(8): 1680-1685. (LI Qing-hui, CHEN Mian, JIN Yan, et al.Indoor evaluation method for shale brittleness and improvement[J]. Chinese Journal of Rock Mechanics and Engineering, 2012, 31(8): 1680-1685. (in Chinese)) [2] 陈国庆, 陈毅, 孙祥, 等. 开放型岩桥裂纹贯通机理及脆性破坏特征研究[J]. 岩土工程学报, 2020, 42(5): 908-915. (CHEN Guo-qing, CHEN Yi, SUN Xiang, et al.Crack coalescence and brittle failure characteristics of open rock bridges[J]. Chinese Journal of Geotechnical Engineering, 2020, 42(5): 908-915. (in Chinese)) [3] 刘新荣, 刘俊, 冯昊, 等. 不同初始卸荷水平和水压下砂岩卸荷力学特性试验研究[J]. 岩土工程学报, 2018, 40(6): 1143-1151. (LIU Xin-rong, LIU Jun, FENG Hao, et al.Experimental research on unloading mechanical properties of sandstone under different initial unloading levels and pore pressures[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(6): 1143-1151. (in Chinese)) [4] 赵毅鑫, 王小良, 郭延定, 等. 基于能量释放率的不同赋存深度砂岩脆性指数研究[J]. 岩石力学与工程学报, 2021, 40(2): 248-262. (ZHAO Yi-xin, WANG Xiao-liang, GUO Yan-ding, et al.Brittleness index of sandstones from different buried depths based on energy release rate[J]. Chinese Journal of Rock Mechanics and Engineering, 2021, 40(2): 248-262. (in Chinese)) [5] MORLEY A.Strength of Materials[M]. London: Longman Green, 1944: 71-72. [6] HETÉNYI M. Handbook of Experimental Stress Analysis[M]. New York: John Wiley, 2017. [7] Ramsey J G.Folding and Fracturing of Rocks[M]. London: McGraw-Hill, 1967: 44-47. [8] 胡训健, 卞康, 谢正勇, 等. 细观结构的非均质性对花岗岩强度及变形影响的颗粒流模拟[J]. 岩土工程学报, 2020, 42(8): 1540-1548. (HU Xun-jian, BIAN Kang, XIE Zheng-yong, et al.Influence of meso-structure heterogeneity on granite strength and deformation with particle flow code[J]. Chinese Journal of Geotechnical Engineering, 2020, 42(8): 1540-1548. (in Chinese)) [9] 史贵才, 葛修润, 卢允德. 大理岩应力脆性跌落系数的试验研究[J]. 岩石力学与工程学报, 2006, 25(8): 1625-1631. (SHI Gui-cai, GE Xiu-run, LU Yun-de.Experimental study on coefficients of brittle stress drop of marble[J]. Chinese Journal of Rock Mechanics and Engineering, 2006, 25(8): 1625-1631. (in Chinese)) [10] 周辉, 孟凡震, 张传庆, 等. 基于应力-应变曲线的岩石脆性特征定量评价方法[J]. 岩石力学与工程学报, 2014, 33(6): 1114-1122. (ZHOU Hui, MENG Fan-zhen, ZHANG Chuan-qing, et al.Quantitative evaluation of rock brittleness based on stress-strain curve[J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(6): 1114-1122. (in Chinese)) [11] 夏英杰, 李连崇, 唐春安, 等. 基于峰后应力跌落速率及能量比的岩体脆性特征评价方法[J]. 岩石力学与工程学报, 2016, 35(6): 1141-1154. (XIA Ying-jie, LI Lian-chong, TANG Chun-an, et al.Rock brittleness evaluation based on stress dropping rate after peak stress and energy ratio[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(6): 1141-1154. (in Chinese)) [12] 侯鹏, 高峰, 张志镇, 等. 基于声发射和能量演化规律评价岩石脆性的方法[J]. 中国矿业大学学报, 2016, 45(4): 702-708. (HOU Peng, GAO Feng, ZHANG Zhi-zhen, et al.Evaluation method of rock brittleness based on acoustic emission and energy evolution[J]. Journal of China University of Mining & Technology, 2016, 45(4): 702-708. (in Chinese)) [13] 侯振坤, 杨春和, 王磊, 等. 基于室内试验的页岩脆性特征评价方法[J]. 东北大学学报(自然科学版), 2016, 37(10): 1496-1500, 1506. (HOU Zhen-kun, YANG Chun-he, WANG Lei, et al.Evaluation method of shale brittleness based on indoor experiments[J]. Journal of Northeastern University (Natural Science), 2016, 37(10): 1496-1500, 1506. (in Chinese)) [14] 刘泉声, 魏莱, 雷广峰, 等. 砂岩裂纹起裂损伤强度及脆性参数演化试验研究[J]. 岩土工程学报, 2018, 40(10): 1782-1789. (LIU Quan-sheng, WEI Lai, LEI Guang-feng, et al.Experimental study on damage strength of crack initiation and evaluation of brittle parameters of sandstone[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(10): 1782-1789. (in Chinese)) [15] GEORGE E A.Brittle Failure of Rock Material-Test Results and Constitutive Models[M]. Rotterdam: A A Balkema Publishers, 1995: 123-128. [16] TARASOV B, POTVIN Y.Universal criteria for rock brittleness estimation under triaxial compression[J]. International Journal of Rock Mechanics and Mining Sciences, 2013, 59: 57-69. [17] 王宇, 李晓, 武艳芳, 等. 脆性岩石起裂应力水平与脆性指标关系探讨[J]. 岩石力学与工程学报, 2014, 33(2): 264-275. (WANG Yu, LI Xiao, WU Yan-fang, et al.Research on relationship between crack initiation stress level and brittleness indices for brittle rocks[J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(2): 264-275. (in Chinese)) [18] MARTIN C D.The Strength of Massive Lac Du Bonnet Granite around Underground Opening[D]. Winnipeg: University of Manitoba, 1993. [19] 刘恩龙, 沈珠江. 岩土材料的脆性研究[J]. 岩石力学与工程学报, 2005, 24(19): 3449-3453. (LIU En-long, SHEN Zhu-jiang.Study on brittleness of geomaterials[J]. Chinese Journal of Rock Mechanics and Engineering, 2005, 24(19): 3449-3453. (in Chinese)) [20] ALTINDAG R, GUNEY A.Predicting the relationships between brittleness and mechanical properties (UCS, TS and SH) of rocks[J]. Scientific Research and Essays, 2010, 5(16): 2107-2118.