Experimental investigation on deformation characteristics and permeability evolution of rock under confining pressure unloading conditions

Abstract

Deformation behavior and hydraulic properties of rock are the two main factors that influence safety of excavation and use of rock engineering due to in situ stress release. The primary objective of this study is to explore deformation characteristics and permeability properties and provide some parameters to character the rock under unloading conditions. A series of triaxial tests with permeability and acoustic emission signal measurement were conducted under the path of confining pressure unloading prior to the peak stress. Deformation behavior and permeability evolution in the whole stress—strain process based on these experimental results were analyzed in detail. Results demonstrate that, under the confining pressure unloading conditions, a good correspondence relationship among the stress—axial strain curve, permeability—axial strain curve and acoustic emission activity pattern was obtained. After the confining pressure was unloaded, the radial strain grew much faster than the axial strain, which induced the volumetric strain growing rapidly. All failures under confining pressure unloading conditions featured brittle shear failure with a single macro shear rupture surface. With the decrease in deformation modulus during the confining pressure unloading process, the damage variable gradually increases, indicating that confining pressure unloading was a process of damage accumulation and strength degradation. From the entire loading and unloading process, there was a certain positive correlation between the permeability and volumetric strain.

Keywords

unloading rock mechanics / permeability evolution / triaxial experiment / acoustic emission / sandstone

References

[1] CookP. In situ pneumatic testing at yucca mountain [J]. International Journal of Rock Mechanics and Mining Sciences, 2000, 37(1): 357-367

[2] WangJ. High-level radioactive waste disposal in China: update 2010 [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2010, 2(1): 1-11

[3] WangJ. On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2014, 6(2): 99-104

[4] JowH. Current status of the United States spent nuclear fuel disposition research and development [J]. World Nuclear Geoscience, 2014, 31(S1): 497-498

[5] The Scientific World Journal, 2014, 2014(6

[6] FangY, WangC, ElsworthD, IshibashiT. Seismicity-permeability coupling in the behavior of gas shales, CO₂, storage and deep geothermal energy [J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2017, 32): 1-10

[7] ZhangY, LuW, ChenM, YanP, HuP. Dam foundation excavation techniques in China: A review [J]. Journal of Rock Mechanics and Geotechnical Engineering, 2013, 5(6): 460-467

[8] LiS, FengX T, LiZ, ChenB, ZhangC, ZhouH. In situ, monitoring of rockburst nucleation and evolution in the deeply buried tunnels of Jinping II hydropower station [J]. Engineering Geology, 2012, 137–138(7): 85-96

[9] BraceW F, WalshJ B, FrangosW T. Permeability of granite under high pressure [J]. Journal of Geophysical Research, 1968, 73(6): 2225-2236

[10] WalshJ B. Effect of pore pressure and confining pressure on fracture permeability [J]. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1981, 18(5): 429-435

[11] OdaM, TakemuraT, AokiT. Damage growth and permeability change in triaxial compression tests of Inada granite [J]. Mechanics of Materials, 2002, 34(6): 313-331

[12] PatersonM S, WongT FExperimental rock deformation–the brittle field [M], 2005, Germany, Springer

[13] HokkaM, BlackJ, TkalichD, FourmeauM, KaneA, AoangN H, LiC C, ChenW W, KuokkalaV T. Effects of strain rate and confining pressure on the compressive behavior of Kuru granite [J]. International Journal of Impact Engineering, 2016, 91: 183-193

[14] HuangR Q, WangX N, ChanL S. Triaxial unloading test of rocks and its implication for rock burst [J]. Bulletin of Engineering Geology and the Environment, 2001, 60(1): 37-41

[15] HuaA Z, YouM Q. Rock failure due to energy release during unloading and application to underground rock burst control [J]. Tunnelling and Underground Space Technology, 2001, 16(3): 241-246

[16] LiuQ, ChengY, JinK, TuQ, ZhaoW, ZhangR. Effect of confining pressure unloading on strength reduction of soft coal in borehole stability analysis [J]. Environmental Earth Sciences, 2017, 76(4): 173

[17] LiangY, LiQ, GuY, ZouQ. Mechanical and acoustic emission characteristics of rock: Effect of loading and unloading confining pressure at the postpeak stage [J]. Journal of Natural Gas Science & Engineering, 2017, 44: 54-64

[18] HuangD, LiY. Conversion of strain energy in triaxial unloading tests on marble [J]. International Journal of Rock Mechanics & Mining Sciences, 2014, 66(1): 160-168

[19] DingQ L, JuF, MaoX B, MaD, YuB Y, SongS B. Experimental investigation of the mechanical behavior in unloading conditions of sandstone after high-temperature treatment [J]. Rock Mechanics and Rock Engineering, 2016, 49(7): 2641-2653

[20] HeM C, MiaoJ L, FengJ L. Rock burst process of limestone and its acoustic emission characteristics under true-triaxial unloading conditions [J]. International Journal of Rock Mechanics and Mining Sciences, 2010, 47(47): 286-298

[21] MiaoJ L, JiaX N, ChengC. The failure characteristics of granite under true triaxial unloading condition [J]. Procedia Engineering, 2011, 261620-1625

[22] RiceT L, NicholsR W, OlsenH W. Low gradient permeability measurements in a triaxial system [J]. Géotechnique, 1985, 35(3): 459

[23] HeilandJ. Permeability of triaxially compressed sandstone: influence of deformation and strain-rate on permeability [J]. Pure and Applied Geophysics, 2003, 1605889-908

[24] DavyC A, SkoczylasF, BarnichonJ D, LebowP. Permeability of macro-cracked argillite under confinement: Gas and water testing [J]. Physics & Chemistry of the Earth Parts A/B/C, 2007, 32(8–14): 667-680

[25] FerferaF M R, SardaJ P, BoutécaM, VinckéO. Experimental study of monophasic permeability changes under various stress paths [J]. International Journal of Rock Mechanics and Mining Sciences, 1997, 34(97): 37.e1-37.e12

[26] HuD W, ZhouH, ZhangF, ShaoJ F. Evolution of poroelastic properties and permeability in damaged sandstone [J]. International Journal of Rock Mechanics and Mining Sciences, 2010, 47(6): 962-973

[27] YuJ, LiH, ChenX, CaiY Y, MuK, ZhangY Z, WuN. Experimental study of permeability and acoustic emission characteristics of sandstone during processes of unloading confining pressure and deformation [J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(1): 69-79

[28] FairhurstC E, HudsonJ A. Draft ISRM suggested method for the complete stress–strain curve for the intact rock in uniaxial compression [J]. International Journal of Rock Mechanics and Mining Sciences, 1999, 36(3): 279-289

[29] WyckoffR D, BotsetH G, MuskatM, ReedD W. The measurement of the permeability of porous media for homogeneous fluids [J]. Review of Scientific Instruments, 1933, 4(7): 394-405

[30] JiaC J, XuW Y, WangH L, WangR B, YuJ, YanJ. Stress dependent permeability and porosity of low-permeability rock [J]. Journal of Central South University, 2017, 24(10): 2396-2405

[31] ZobackM D, ByerleeJ D. The effect of microcrack dilatancy on the permeability of westerly granite [J]. Journal of Geophysical Research Atmospheres, 1975, 80(5): 752-755

[32] BiotM A. General theory of three-dimensional consolidation [J]. Journal of Applied Physics, 1941, 12: 155-164

[33] QiuS L, FengX T, ZhangC Q, ZhouH, SunF. Experimental research on mechanical properties of deep-buried marble under different unloading rates of confining pressures [J]. Chinese Journal of Rock Mechanics and Engineering, 2010, 29(9): 1807-1817

[34] LemaitreJ. A continuous damage mechanics model for ductile fracture [J]. Journal of Engineering Materials and Technology, 1985, 107(1): 83-89

[35] LemaitreJ, DesmoratREngineering damage mechanics: ductile, creep, fatigue and brittle failures [M], 2005, Germany, Springer

[36] WuY Q, CaoG Z, WangD W. Microfraturing process of rock by real-time observation of X-ray CT [J]. Chinese Journal of Applied Mechanics, 2005, 22(3): 484-490