Abstract：To investigate the effect of the unloading rate on the unloading-induced slip mechanism of shale，the slip start-up of jointed shales is triggered by stepwise-unloading confining pressure with constant axial stress using MTS815 loading system，wherein the unloading rates are 0.01，0.1，1 and 10 MPa/min respectively. The results show that：(1) The asperity altitude of the saw-cut joint decreases and the roughness increases due to slip deformation. With the increase of the unloading rate，the joint roughness coefficient(JRC) of saw-cut morphology increases by 22.68%，44.82%，38.49% and 49.89%，respectively. (2) The slip velocity increases with the elevation of the unloading rate，and the average velocity of quasi-static slip is two orders of magnitude higher than that of creep slip at the same unloading rate. The creep slip average velocities are 4.87×10－6，2.52×10－5，3.99×10－4 and 3.29×10－3 mm/s，respectively. The corresponding average quasi-static slip velocities are 7.39×10－4，5.98×10－3，2.8×10－2 and 1.2×10－1 mm/s，respectively. (3) The unloading amount of confining pressure is the smallest and the friction strengthening effect is the weakest under 0.1 MPa/min. Under 0.01 MPa/min，the friction strength of the sample is well enhanced in the long-term creep slip，and the friction strength is weakened in the dynamic slip. At the unloading rate of 1 and 10 MPa/min，the sample will slip in a short time，and the friction strength is enhanced in the dynamic slip. (4) There is a critical unloading rate between 0.1–1 MPa/min，and the unloading amount of confining pressure is the smallest when the sample slips at the critical unloading rate. It presents that the strain energy accumulated on the joint plane is smaller and the energy mainly acts on the micro-convexities to break the interlocking during the slip，so the energy released after the slip is the smallest and produces the minimum shear displacement，which is of great significance for the safety of rock mass engineering.
[1] WU W，ZHAO Z H，DUAN K，et al. Unloading-induced instability of a simulated granular fault and implications for excavation-induced seismicity[J]. Tunnelling and Underground Space Technology，2017，63：154–161.
[2] FOULGER G R，WILSON M P，GLUYAS J G，et al. Global review of human-induced earthquakes[J]. Earth-Science Reviews，2017，178：438–514.
[3] 李志华，窦林名，陆振裕，等. 采动诱发断层滑移失稳的研究[J]. 采矿与安全工程学报，2010，27(4)：499–504.(LI Zhihua，DOU Linming，LU Zhenyu，et al. Study of the fault slide destabilization induced by coal mining[J]. Journal of Mining and Safety Engineering，2010，27(4)：499–504.(in Chinese))
[4] 赵同彬，程康康，魏 平，等. 含弱面岩石滑移破坏及锚固控制试验研究[J]. 采矿与安全工程学报，2017，34(6)：1 081–1 087.(ZHAO Tongbin，CHENG Kangkang，WEI Ping，et al. Study on slip failure of rock with weak plane and anchorage control mechanism[J]. Journal of Mining and Safety Engineering，2017，34(6)：1 081–1 087.(in Chinese))
[5] WANG L，KWIATEK G，RYBACKI E，et al. Injection-induced seismic moment release and laboratory fault slip：Implications for fluid-induced seismicity[J]. Geophysical Research Letters，2020，47(22)：1–11.
[6] 赵扬锋，荆 刚，樊 艺，等. 断层黏滑失稳过程微震与电荷信号时频特征研究[J]. 岩石力学与工程学报，2020，39(7)：1 385–1 395. (ZHAO Yangfeng，JING Gang，FAN Yi，et al. Experimental study on the microseism and charge signal time-frequency characteristics in the process of fault stick-slip instability[J]. Chinese Journal of Rock Mechanics and Engineering，2020，39(7)：1 385–1 395.(in Chinese))
[7] 张重远，何满潮，陶志刚，等. 发震断层震前应力降现象及其机制探讨[J]. 岩石力学与工程学报，2021，40(5)：916–927.(ZHANG Chongyuan，HE Manchao，TAO Zhigang，et al. Discussion on stress drop mechanisms of seismogenic faults before earthquakes[J]. Chinese Journal of Rock Mechanics and Engineering，2021，40(5)：916–927.(in Chinese))
[8] 宋义敏，马少鹏，杨小彬，等. 断层黏滑动态变形过程的实验研究[J]. 地球物理学报，2012，55(1)：171–179.(SONG Yimin，MA Shaopeng，YANG Xiaobin，et al. Experimental study on the dynamic displacement evolution of fault in stick-slip process[J]. Chinese Journal of Geophysics，2012，55(1)：171–179.(in Chinese))
[9] JI Y L，WU W，ZHAO Z H. Unloading-induced rock fracture activation and maximum seismic moment prediction[J]. Engineering Geology，2019，262：105352.
[10] WU W，ZOU Y，LI X，et al. An unload-induced direct-shear model for granular gouge friction in rock discontinuities[J]. Review of Scientific Instruments，2014，85(9)：093902.
[11] MENG F，WONG L N Y，ZHOU H，et al. Shear rate effects on the post-peak shear behavior and acoustic emission characteristics of artificially split granite joints[J]. Rock Mechanics and Rock Engineering，2019，52：2 489.
[12] 李海波，张天航，邵 蔚，等. 三轴压缩情况下岩石变形特征的滑移型裂纹模拟[J]. 岩石力学与工程学报，2005，24(17)：3 119–3 124. (LI Haibo，ZHANG Tianhang，SHAO Wei，et al. Simulation of deformation behavior of rock material under triaxial compression based on sliding crack model[J]. Chinese Journal of Rock Mechanics and Engineering，2005，24(17)：3 119–3 124.(in Chinese))
[13] YE Z，GHASSEMI A. Heterogeneous fracture slip and aseismic-seismic transition in a triaxial injection test[J]. Geophysical Research Letters，2020，47(14)：e2020GL087739.
[14] 何满潮，赵 菲，杜 帅，等. 不同卸载速率下岩爆破坏特征试验分析[J]. 岩土力学，2014，35(10)：2 737–2 747.(HE Manchao，ZHAO Fei，DU Shuai，et al. Rockburst characteristics based on experimental tests under different unloading rates[J]. Rock and Soil Mechanics，2014，35(10)：2 737–2 747.(in Chinese))
[15] 张 凯，周 辉，潘鹏志，等. 不同卸荷速率下岩石强度特性研究[J]. 岩土力学，2010，31(7)：2 072–2 078.(ZHANG Kai，ZHOU Hui，PAN Pengzhi，et al. Characteristics of strength of rocks under different unloading rates[J]. Rock and Soil Mechanics，2010，31(7)：2 072–2 078.(in Chinese))
[16] 陈卫忠，吕森鹏，郭小红，等. 基于能量原理的卸围压试验与岩爆判据研究[J]. 岩石力学与工程学报，2009，28(8)：1 530–1 540. (CHEN Weizhong，LU Senpeng，GUO Xiaohong，et al. Research on unloading confining pressure tests and rockburst criterion based on energy theory[J]. Chinese Journal of Rock Mechanics and Engineering，2009，28(8)：1 530–1 540.(in Chinese))
[17] 刘 婕，张黎明，丛 宇，等. 真三轴应力路径花岗岩卸荷破坏力学特性研究[J]. 岩土力学，2021，42(8)：2 069–2 077.(LIU Jie，ZHANG Liming，CONG Yu，et al Research on the mechanical characteristics of granite failure process under true triaxial stress path[J]. Rock and Soil Mechanics，2021，42(8)：2 069–2 077.(in Chinese))
[18] HAN Y，MA H，YANG C. The mechanical behavior of rock salt under different confining pressure unloading rates during compressed air energy storage(CAES)[J]. Journal of Petroleum Science and Engineering，2021，196：107676.
[19] XU H，FENG X T，YANG C X，et al. Influence of initial stresses and unloading rates on the deformation and failure mechanism of Jinping marble under true triaxial compression[J]. International Journal of Rock Mechanics and Mining Sciences，2019，117：90–104.
[20] BRADY B H，BROWN E T. Rock mechanics for underground mining[M]. [S. l.]：Springer Science and Business Media，1993.
[21] KOHLI A H，ZOBACK M D. Frictional properties of shale reservoir rocks[J]. Journal of Geophysical Research，2013，118(9)：5 109–5 125.
[22] YE Z，GHASSEMI A. Injection-induced shear slip and permeability enhancement in granite fractures[J]. Journal of Geophysical Research：Solid Earth，2018，123：9 009–9 032.
[23] ELLSWORTH W L. Injection-induced earthquakes[J]. Science，2013，341(6142)：1225942.
[24] 李宏哲，夏才初，王晓东，等. 含节理大理岩变形和强度特性的试验研究[J]. 岩石力学与工程学报，2008，27(10)：2 118–2 123.(LI Hongzhe，XIA Caichu，WANG Xiaodong，et al. Experimental study on deformation and strength properties of jointed marble specimens[J]. Chinese Journal of Rock Mechanics and Engineering，2008，27(10)：2 118–2 123.(in Chinese))
[25] 班力壬，戚承志，李晓照，等. 考虑真实接触微凸体的岩石节理三维粗糙度指标[J]. 煤炭学报，2020，45(12)：4 052–4 061.(BAN Liren，QI Chengzhi，LI Xiaozhao，et al. A 3D quantified surface description for rock joint based on the real contact asperities[J]. Journal of China Coal Society，2020，45(12)：4 052–4 061.(in Chinese))
[26] ISRM. Rock characterization，testing and monitoring-ISRM suggested methods[C]// Suggested Methods for the Quantitative Description of Discontinuities in Rock Masses. Pergamon，Oxford：[s. n. ]，1981：3–52.
[27] MYERS N. Characterization of surface roughness[J]. Elsevier，1962，5(3)：182–189.
[28] TSE R，CRUDEN D. Estimating joint roughness coefficients[J]. International Journal of Rock Mechanics and Mining Sciences，1979，16(5)：303–307.
[29] 曹秋菊，王金安. 断裂岩石粗糙性与岩体抗剪强度和机制的实验研究[J]. 中国矿业，2012，21(5)：107–111. (CAO Qiuju，WANG Jin?an. Experimental study on roughness and long shear strength of fracture rock[J]. China Mining Magazine，2012，21(5)：107–111.(in Chinese))
[30] INDRARATNA B，HAQUE A. Experimental study of shear behavior of rock joints under constant normal stiffness conditions[J]. International Journal of Rock Mechanics and Mining Sciences，1997，34(3)：141–155.
[31] BRACE F P，TABOR D. The friction and lubrication of solids[J]. Oxford：Clarendon Press，1951，19(7)：428.
[32] MARONE C. Laboratory-derived friction laws and their application to seismic faulting[J]. Annual Review of Earth and Planetary Sciences，1998，26(1)：643–696.
[33] 秦忠诚，刘贝贝，陶雄兵. 采掘诱发断层冲击地压的能量判据及监测[J]. 煤炭技术，2016，35(1)：105–108.(QIN Zhongcheng，LIU Beibei，TAO Xiongbing. Energy criterion and monitoring of rock burst induced by mining[J]. Coal Technology，2016，35(1)：105–108.(in Chinese))
2023, Vol. 42 
