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  2023, Vol. 42 Issue (8): 1959-1972    DOI: 10.13722/j.cnki.jrme.2022.1114
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Influence of unloading rate on mechanical behaviors of shales during#br# unloading-induced slip processes
JI Haoqi,LIU Richeng,YU Liyuan,LI Shuchen,WANG Xiaolin
(State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology,Xuzhou,Jiangsu 221116,China)
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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.
Key wordsrock mechanics      unloading-induced slip      unloading rate      surface roughness      friction coefficient     
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JI Haoqi
LIU Richeng
YU Liyuan
LI Shuchen
WANG Xiaolin
Cite this article:   
JI Haoqi,LIU Richeng,YU Liyuan, et al. Influence of unloading rate on mechanical behaviors of shales during#br# unloading-induced slip processes[J]. , 2023, 42(8): 1959-1972.
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http://rockmech.whrsm.ac.cn/EN/10.13722/j.cnki.jrme.2022.1114      OR      http://rockmech.whrsm.ac.cn/EN/Y2023/V42/I8/1959
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