In order to investigate the dilatancy of irregular columnar jointed rock masses (ICJRM) under unloading conditions, a series of three-dimensional discrete element numerical models of ICJRM with seven column dip angles were established, and the compressive strength typical failure characteristics and dilatancy evolution of ICJRM were obtained through numerical conventional triaxial compression tests under unloading confining pressure conditions. The results show that: The shape of peak deviatoric stress Δσ1f vs. dip angle βj curve resembled the letter “J”, where the peak deviatoric stress has the minimum value at βj =60°, and reached its maximum value at βj =90°, and the typical failure modes included splitting along the column and columnar joint surface, shear slipping along the columnar joint surface, and the compression-flexure destabilization of the columns; The dilatancy of irregular columnar jointed rock mass under unloading condition was closely related to the initial confining pressure and dip angle, and the corresponding volumetric strain increment obtained larger values when the dip angles ranged from 30° to 60° indicating a significant dilatancy.
[1] 徐松年. 火山岩柱状节理构造研究[M]. 杭州: 杭州大学出版社, 1995. (Xu Songnian. Columnar Joint Structure of Mesozolc Acidic Volcanic Rocks[M] Hangzhou: Hangzhou University Press, 1995. (in Chinese))
[2] 江权, 冯夏庭, 樊义林, 等. 柱状节理玄武岩各向异性特性的调查与试验研究[J]. 岩石力学与工程学报, 2013, 32(12): 2527-2535. (Jiang Quan, Feng Xiating, Fan Yilin, et al. Survey and laboratory study of anisotropic properties for columnar jointed basaltic rock mass[J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(12): 2527-2535. (in Chinese))
[3] 倪邵虎, 何世海, 陈益民, 等. 柱状节理玄武岩的破坏模式、破坏机制及工程对策[J]. 岩石力学与工程学报, 2016, 35(增1): 2549-2560. (Ni Shaohu, He Shihai, Chen Yimin, et al. The failure modes, failure mechanisms and countermeasures of columnar jointed basalt rock mass[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(Supp.1): 2549-2560. (in Chinese))
[4] Fan Q X, Feng X T, Weng W L, et al. Unloading performances and stabilizing practices for columnar jointed basalt: A case study of Baihetan hydropower station[J]. Journal of Rock Mechanics and Geotechnical Engineering, 2017, 9: 1041-1053.
[5] Lin P, Shi J, Wei P C, et al. Shallow unloading deformation analysis on Baihetan super-high arch dam foundation[J]. Bulletin of Engineering Geology and the Environment, 2019, 78: 5551-5568.
[6] 张春生, 徐建荣, 吉华, 等. 白鹤滩水电站柱状节理玄武岩力学特性及松弛控制[J]. 岩石力学与工程学报, 2022, 41(7): 1297-1309. (Zhang Chunsheng, Xu Jianrong, Ji Hua, et al. Mechanical characteristics and relax control of columnar jointed basalt at Baihetan hydropower station[J]. Chinese Journal of Rock Mechanics and Engineering, 2022, 41(7): 1297-1309. (in Chinese))
[7] 丰光亮, 张建聪, 江权, 等. 开挖强卸荷下柱状节理岩体时效破裂过程协同观测与机制分析[J]. 岩石力学与工程学报, 2021, 40(增2): 3041-3051. (Feng Guangliang, Zhang Jiancong, Jiang Quan, et al. Synergistic observation and mechanism analysis of time-dependent fracture process of columnar jointed rock mass under strong unloading during excavation[J]. Chinese Journal of Rock Mechanics and Engineering, 2021, 40(Supp.2): 3041-3051. (in Chinese))
[8] 郝宪杰, 冯夏庭, 李邵军, 等. 柱状节理玄武岩隧洞破坏模式及其力学机制模拟[J]. 岩土力学, 2015, 36(3): 837-846. (Hao Xianjie, Feng Xiating, Li Shaojun, et al. Failure mode of columnar jointed basalt tunnel and its mechanism simulation[J]. Rock and Soil Mechanics, 2015, 36(3): 837-846. (in Chinese))
[9] 孟国涛, 樊义林, 江亚丽, 等. 白鹤滩水电站巨型地下洞室群关键岩石力学问题与工程对策研究[J]. 岩石力学与工程学报, 2016, 35(12): 2549-2560. (Meng Guotao, Fan Yilin, Jiang Yali, et al. Key rock mechanical problems and measures for huge caverns of Baihetan hydropower plant[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(12): 2549-2560. (in Chinese))
[10] 倪卫达, 石安池. 白鹤滩水电站柱状节理玄武岩卸荷损伤数值试验研究[J]. 长江科学院院报, 2017, 34(10): 85-90. (Ni Weida, Shi Anchi. Numerical study on unloading damage of columnar jointed basalt at Baihetan hydropower station[J]. Journal of Yangze River Scientific Research Institute, 2017, 34(10): 85-90. (in Chinese))
[11] Jin C Y, Yang C X, Fang D, et al. Study on the failure mechanism of basalts with columnar joints in the unloading process on the basis of an experimental cavity[J]. Rock Mechanics and Rock Engineering, 2015, 48(3): 1275-1288.
[12] 金长宇, 侯晓乐, 刘冬, 等. 柱状节理玄武岩卸荷力学特性的数值模拟[J]. 东北大学学报(自然科学版),2016, 37(2): 243-248. (Jin Changyu, Hou Xiaole, Liu Dong, et al. Numerical Simulation of Mechanical Properties of Columnar Jointed Basalt Under Unloading Condition. Journal of Northeastern University (Natural Science), 2016, 37(2): 243-248. (in Chinese))
[13] Wang Y, Gong B, Tang C. Numerical Investigation on Anisotropy and Shape Effect of Mechanical Properties of Columnar Jointed Basalts Containing Transverse Joints[J]. Rock Mechanics and Rock Engineering, 2022, 55: 7191-7222.
[14] Zhao D, Xia Y, Zhang C. et al. Anew method to investigate the size effect and anisotropy of mechanical properties of columnar jointed rock mass[J]. Rock Mechanics and Rock Engineering, 2023, 56: 2829-2859.
[15] Wang Yongyi, Gong Bin, Tang Chunan. Size effect and lateral pressure effect on the mechanical resistance of columnar jointed basalt[J]. International Journal of Rock Mechanics and Mining Sciences, 2023, 171: 105571.
[16] 肖维民, 田梦婷, 黄巍, 等. 不规则柱状节理网络随机模拟方法研究[J]. 地下空间与工程学报, 2021, 17(4): 1072-1079, 1090. (Xiao Weimin, Tian Mengting, Huang Wei, et al. Study on a Method for Random Simulation of Irregular Columnar Joints Network[J]. Chinese Journal of Underground Space and Engineering, 2021, 17(4): 1072-1079, 1090. (in Chinese))
[17] 田梦婷. 不规则柱状节理岩体卸荷力学特性试验研究[D]. 成都: 四川农业大学, 2021. (Tian Mengting. Experimental study on unloading mechanical properties of irregular columnar jointed rock mass[D]. Chengdu: Sichuan Agricultural University, 2021. (in Chinese))
[18] 张庆浩. 柱状节理岩体三轴卸荷破坏规律及声发射特征研究[D]. 泰安: 山东农业大学, 2022. (Zhang Qinghan. Study on the Failure Law and Acoustic Emission Characteristics of Columnar Jointed Rock Mass under Triaxial Unloading[D]. Shandong: Shandong Agricultural University, 2022. (in Chinese))
[19] Bridgman P W. Volume Changes in the Plastic Stages of Simple Compression[J]. Journal of Applied Physics, 1949, 20(12): 1241-1251.
