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タイトル Experimental Study on Long-term Permeability Change at different temperatures
著者 宋 忱潞・安原英明・中島伸一郎・岸田 潔
出版 第54回地盤工学研究発表会発表講演集
ページ 17〜18 発行 2019/06/20 文書ID rp201905400009
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  • タイトル
  • Experimental Study on Long-term Permeability Change at different temperatures
  • 著者
  • 宋 忱潞・安原英明・中島伸一郎・岸田 潔
  • 出版
  • 第54回地盤工学研究発表会発表講演集
  • ページ
  • 17〜18
  • 発行
  • 2019/06/20
  • 文書ID
  • rp201905400009
  • 内容
  • 0009第 54 回地盤工学研究発表会(さいたま市) 2019 年 7 月F - 00Experimental Study on Long-term Permeability Change at different temperaturesPermeability Long-term Mineral compositionKyoto UniversityEhime UniversityYamaguchi UniversityKyoto UniversityMemberMemberMemberMember○Chenlu SongHideaki YasuharaShinichiro NakashimaKiyoshi Kishida1 Introductionprocess, the temperature is gradually increased until60 ℃.(c) At 60℃, the confining pressure is also holding at 3.0MPa for 120 holding days and permeability test iscarried intermittent dates. Distilled water is utilized inthis experiment for easily grasping the mineral variation.Moreover, extracted water from the rock fracture is alsoevaluated after each permeability test.It is thought that the underground water flows around the rockmass would be altered under various conditions. The coupledTHMC(temperature-hydro-mechanical-chemical) processesmay exert a significant influence on the subsurface waterflow around the fractured rock mass. Several previous studiesfocus on the hydraulic properties of the rock fractures undercoupled conditions [1,2]. However, many of laboratoryworks do not examine the characteristic of the permeabilityevolution in the rock fractures in long-term. Moreover, theproperties of hydraulic aperture variation in long-term alsoneed to be clarified. In this study, several long-termpermeability tests on granite with a single fracture underconstant confining condition were performed. Additionally,solute mineral components generated within the fractureaperture during the permeability test were also measured.Consequently, it is discussed that the permeability of fracturewas changed for the long-term under various confining andthermal conditions.33.34 mm101.21 mmSample 1#49.28 mmLow2 Experimental conditions and methodologyA cylindrical granite specimen with a diameter of 49.3 mmand a length of 101.2 mm, was split by the Brazilian test tocreate a single fracture along the cylinder axis. Themorphology of the surface roughness was measured asshown in Fig.1. It will be utilized for checking the roughnesssurfaces evolution under different conditions at the pre- andpost-experiment. The granite specimen sealed with the heatshrinkable tube was installed into the triaxial cell as shown inFig.2 [3]. Long-term permeability tests were conducted atconstant confining stress for 120 holding days and with twodifferent temperatures, 20 and 60 ℃, as shown in Fig.3. Theexperiment process was consisted in three steps,(a) At 20 ℃, the confining pressure until 3.0 MPa isincreasing, and then the confining pressure is holding for120 holding days. Permeability test is carriedintermittent dates.(b) After 120 holding days measurement, 1 cycle ofloading-unloading was employed. After the unloading15.23 mmRoughnessHighFig.1 Cylindrical granite specimen and the morphology of the surfacesroughnessFig.2 Triaxial cell and flow measurement system utilized in this study[1]Experimental Study on Long-term Permeability Change at differenttemperatures○Chenlu Song, Kiyoshi KishidaKyoto UniversityHideaki Yasuhara, Ehime University, Shinichiro Nakashima, Yamaguchi University17 dissolution might occur on the free surface greater than thefracture contact area, which will lead to the increase of theaperture. Additionally, it will alter the permeability evolution.Long-term 20℃Long-term 60℃3.52Permeability (10-13m )4Fig.3 Procedure of the permeability tests3 Experimental resultsFig.4 shows the temporal change of the permeability undertwo different temperature conditions. At 20 oC, permeabilitydecreasing can be summarized as two stages. At the first stage,permeability decreased sharply within several days, then itdecreased again after a short stable period. It can be thoughtthat at the second reduction stage, mechanical creepcompaction leads to the permeability evolution. Moreover,the geochemical reaction such as the mineral dissolution andreprecipitation might also altered the permeability. Fig.5shows the element concentrations at 20 oC, the concentrationsof the elements of Si, Na, Ca are larger than others. From 80to 120 holding days, those elements show slight fluctuation.Mineral dissolution changing can be thought to explain thepermeability decreasing. At 60 oC, the permeability is lowerthan that at 20 oC before 60 holding days. Permeability wasaltered at a higher temperature. However, after 60 holdingdays, permeability had a tendency to increase and seemsunstable. It is different from some researchers thatpermeability decrease at a higher temperature. A highertemperature might drive the geochemical reaction, mineraldissolution of the free surfaces is larger than the dissolution atthe contact area [4]. Then, it might enlarge the aperture andincreases the permeability.32.521.510.5020406080100120Time (Day)Fig.4 The temporal change of the permeability evolution under constantconfining pressure of 3.0 MPa and temperatures of 20 and 60 oC10-3Concentration (mol/L)SiAlKFeMgNaCa10-410-510-6020406080100120Time (Day)Fig.5 Evolution of the mineral composition at 20 oCReferences[1]. Polak, A., Elsworth, D., and Liu, J. S. Spontaneous switching ofpermeability changes in a limestone fracture with net dissolution[J].4. ConclusionsThis paper reported two long-term experiment works of thepermeability tests under the constant normal stress and twodifferent temperatures. At 20℃, the permeability decreasedmonotonically. After about 30 holding days, the permeabilitydecreased should be thought to be due to mechanical creepdeformation. Pressure solution might also occur at thefracture asperities.Based on the mineral composition analysis, the permeabilityvariation depending on chemo-mechanical interaction on thefracture surface roughness can be confirmed. At 60 ℃, at theinitial phase, the permeability value is always lower than thatat 20 ℃. After about 60 holding days, the permeability hadan increasing tendency. It can be thought that the mineralWater Resources Research. 40(W03502): 1 029–1 038. 2004.[2].Min,K.B., Rutqvist,J., Elsworth, D. Chemically and mechanicallymediated influences on the transport and mechanical characteristics ofrock fractures[J]. International Journal of Rock Mechanics and MiningSciences. 46(1): 80–89. 2009.[3]. Yasuhara, H., Hasegawa, D. Nakashima, s., Yano, T. and Kishida, K.,Experimental evaluation of fracture permeability in granite undertemperature and stress controlled conditions. Japanese GeotechnicalJournal, 8(1), pp.71-79, 2013.[4].Yasuhara, H., Elsworth, D., and Liu, J. S., Halleck,P. Spontaneousswitching between permeability enhancement and degradation infractures in carbonate: Lumped parameter representation ofmechanically- and chemically-mediated dissolution. Transp. PorousMedia. 65, 385–409, doi:10.1007/s11242-006-6386-2. 2006.18
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