1. Key Laboratory of New Technology for Construction of Cities in Mountain Area, Ministry of Education, Chongqing University, Chongqing 400045, China; 2. School of Civil and Transportation Engineering, Hebei University of Technology, Tianjin 300401, China; 3. Institute of Geotechnical Engineering, Chongqing Jiaotong University, Chongqing 400074, China
Abstract：Rock excavation and river incision result in stress unloading in one or more directions, which leads to the redistribution of stress fields of rock masses in the influenced zone. The rock masses in the unloading zone commonly bear tension-shear stress, making the failure of unloading rocks exhibit obvious tensile property. However, due to the limitation of test technology, it is still quite difficult to study the shear mechanical behavior of rock under the action of normal tensile stress. In this study, a tension double-shear test auxiliary device that can be used by conventional direct shear testing machine is designed to convert the normal compressive force to the tensile one. The direct shear tests on sandstone under tensile normal stress are carried out using this device. The results show that under the tension-shear stress, the curves of shear stress versus shear displacement before peak stress only show two deformation stages of initial nonlinear deformation and linear deformation (namely without yield stage before peak). The shear strength and shear stiffness of sandstone gradually decrease with the increase of the normal tensile stress. Compared with the Mohr-Coulomb criterion, the Hoek-Brown criterion is better in describing the strength characteristics of sandstone under tensile shear stress. Besides, as the normal tensile stress increases, the rupture surface of rock specimen has more obvious tension and is straighter in shape.
[1] 张倬元, 王仕天, 王兰生, 等. 工程地质分析原理[M]. 北京: 地质出版社, 2009. (ZHANG Zhuo-yuan, WANG Shi-tian, WANG Lan-sheng, et al.Principles of engineering geology[M]. Beijing: Geological Publishing House, 2009. (in Chinese)) [2] HUANG R Q, HUANG D.Evolution of rock cracks under unloading condition[J]. Rock mechanics and Rock Engineering, 2014, 47(2): 453-466. [3] ETHERIDGE M A.Differential stress magnitudes during regional deformation and metamorphism: upper bound imposed by tensile fracturing[J]. Geology, 1983, 11(4): 231-234. [4] 黄润秋, 黄达, 段绍辉, 等. 锦屏Ⅰ级水电站地下厂房施工期围岩变形开裂特征及地质力学机制研究[J]. 岩石力学与工程学报, 2011, 30(1): 23-35. (HUANG Run-qiu, HUANG Da, DUAN Shao-hui, et al.Geomechanics mechanism and characteristics of surrounding rock mass deformation failure in construction phase for underground powerhouse of Jinping Ⅰ hydropower station[J]. Chinese Journal of Rock Mechanics and Engineering,(in Chinese)) [5] 赵宝云, 刘东燕, 朱可善, 等. 重庆红砂岩单轴直接拉伸蠕变特性试验研究[J]. 岩石力学与工程学报, 2011, 30(增刊2): 3960-3965. (ZHAO Bao-yun, LIU Dong-yan, ZHU Ke-shan, et al.Experimental research on creep characteristics of Chongqing red sandstone under direct tension[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30(S2): 3960-3965. (in Chinese)) [6] 许江, 刘婧, 吴慧, 等.压剪应力条件下砂岩开裂扩展过程的试验研究[J]. 岩石力学与工程学报, 2013, 32(增刊2): 3042-3048. (XU Jiang, LIU Jing, WU Hui, et al.Test study of sandstone cracking and propagation process under compressive-shear stress[J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(S2): 3042-3048. (in Chinese)) [7] 李建林. 岩石拉剪流变特性的试验研究[J]. 岩土工程学报, 2000, 22(3): 299-303. (LI Jian-lin.A test study on tension shear creep of rock[J]. Chinses Journal of Geotechnical Engineering, 2000, 22(3): 299-303. (in Chinese)) [8] RAMSEY J M, CHESTER F M.Hybrid fracture and the transition from extension fracture to shear fracture[J]. Nature, 2004, 428(6978): 63. [9] 周辉, 卢景景, 徐荣超, 等. 硬脆性大理岩拉剪破坏特征与屈服准则研究[J]. 岩土力学, 2016, 37(2): 305-314. (ZHOU Hui, LU Jing-jing, XU Rong-chao, et al.Research on tension-shear failure characteristics and yield criterion of hard brittle marble[J]. Rock and Soil Mechanics, 2016, 37(2): 305-314. (in Chinese)) [10] CEN D, HUANG D.Direct shear tests of sandstone under constant normal tensile stress condition using a simple auxiliary device[J]. Rock Mechanics & Rock Engineering, 2017, 50(6): 1425-1438. [11] 李守定, 李晓, 郭静芸, 等. 岩石拉伸剪切破裂试验研究[J]. 工程地质学报, 2014, 22(4): 655-666. (LI Shou-ding, LI Xiao, GUO Jing-yun, et al.Research of rock failure testing under combined shear and tension[J]. Journal of Engineering Geology, 2014, 22(4): 655-666. (in Chinese)) [12] 许江, 刘婧, 程立朝, 等. 压剪应力条件下砂岩双面剪切细观开裂扩展演化特性试验研究[J]. 岩石力学与工程学报, 2014, 33(4): 649-657. (XU Jiang, LIU Jing, CHEN Li-chao, et al.Mesoscopic cracking and expansion of double sheared sandstone under compressive-shear stress[J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(4):649-657. (in Chinese)) [13] YANG X L, YIN J H.Upper bound solution for ultimate bearing capacity with a modified Hoek-Brown failure criterion[J]. International Journal of Rock Mechanics & Mining Sciences, 2005, 42(4): 550-560. [14] GALINDO R A, SERRANO A, OLALLA C.Ultimate bearing capacity of rock masses based on modified Mohr-Coulomb strength criterion[J]. International Journal of Rock Mechanics & Mining Sciences, 2017, 93: 215-225. [15] HOEK E, BROWN E T.Empirical strength criterion for rock masses[J]. Journal of the Geotechnical Engineering Division, 1980, 106: 1013-1035. [16] 周辉, 李震, 杨艳霜, 等. 岩石统一能量屈服准则[J].岩石力学与工程学报, 2013, 32(11): 2170-2184. (ZHOU Hui, LI Zhen, YANG Yan-shuang, et al.Unified energy yield criterion of rock[J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(11): 2170-2184. (in Chinese))
