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| Title: | 平滑節理水力與力學內寬的量測-岩石節理之水力力學耦合行為;Measuring the mechanical and hydraulic apertures of smooth, rock joints using porosimeter/permeameter—Viewpoints from hydromechanical couple behaviors |
| Authors: | 阮玄辛;Nguyen, Xuan Xinh |
| Contributors: | 應用地質研究所 |
| Keywords: | 節理水力與力學內寬;高圍壓;YOKO2量測系統;節理體積量測;脈衝衰減法;平滑;線鋸切割拋光節理試體;鋁與板岩;葉理;異向性;Hydraulic and mechanical apertures;High confining stress;YOKO2 system;Joint volume measurement;Steady-state test;Pulse-decay test;Smooth, saw-cut and polished aluminum;Saw-cut and foliated slate;Anisotropic behavior |
| Date: | 2023-07-12 |
| Issue Date: | 2023-10-04 16:21:29 (UTC+8) |
| Publisher: | 國立中央大學 |
| Abstract: | 流體流經岩體討論主題不論是對岩盤工程或地球科學都是非常重要。應力作用下單一岩石節理的水力內寬(e)是模擬流體流經受應力之岩體之關鍵變數，由於節理在不同正向應力下力學內寬(E)之預測模型已相當完備，因此承受不同應力節理之水力內寬可以很容易地利用E - e關係進行估算。然而，力學內寬試驗常使用正向位移法(normal displacement method，ND 法)加以量測，因而需要「估計」初始內寬。這種試驗方法導致量測結果之不確定性可以傳播到E - e關係式中。本研究使用原設計用來量測岩石孔隙率與滲透率之YOKO 2系統，在3至120 MPa的圍壓下，針對使用線鋸切割後拋光鋁製節理試體以及具葉理之板岩試體(均屬平滑節理)，進行力學(節理體積量測法，JV法)/水力內寬(穩態法，SS法)室內量測。此外，本研究提出了一個新的脈衝衰減平衡方法(PDB法，暫態法)，利用承受圍壓之同一顆試體同時量測岩石節理 e 和 E，為能達成此一目的，YOKO2系統採封閉系統，在高達60 MPa的圍壓(正向應力)下測量線鋸切割後拋光的板岩試體之e和E。根據壓力衰減曲線的分析確定水力內寬，而透過節理體積量測(JV法)確定平衡壓力以確定力學內寬。
本研究重要發現如下：(1)使用穩態法和節理體積法量測具有相同節理表面之線鋸切割後拋光平滑鋁製節理試體的 e 和 E，有很好的重複性，並可使用雙曲函數擬合e 和 E 的應力相依性；(2)本研究建議之PDB方法，可同時量測線鋸切割後拋光板岩平滑節理試體的 e 和 E，並可使用雙曲函數擬合e 和 E 的應力相依性；(3)節理體積(JV法)量測力學內寬，可降低利用量測節理閉合的ND法初始內寬估計所導致之不確定性，同時可提升E "- " e關係的可靠性。(4)當採用JV方法以降低初始內寬估計的影響時，需要注意的是，即使岩石節理試體完整岩石基質本身孔隙率小於0.1%，此一體積對力學內寬測量的貢獻也不容忽視。但是，低滲透性岩石的基質滲透率對於穩態法輛測之影響可以忽略不計; (5)忽略二次傅希海默(Forchheimer）項會導致低估水力內寬; (6)採用PDB暫態方法估計的水力內寬與穩態法試驗量測結果接近; (7)高正向應力下的平滑節理，暫態法壓力脈衝衰減分析使用簡化和嚴謹解析解估計獲得之水力內寬相當一致，然而，低正向應力下粗糙的岩石節理，則不宜忽略岩石節理的比儲蓄率，採簡化解析解引起的水力內寬估計誤差可能是不可忽視的; (8)透過YOKO2封閉系統PDB法可量測的水力內寬e為幾微米到幾十微米。雖然可量測的力學內寬E低於1微米，但E的最佳量測範圍約為1000到10000微米。為了協調水力和力學內寬最佳量測範圍，本研究建議使用常規之三軸試驗典型試體大小進行試體製備; (9)具有未開裂葉理板岩有效孔隙率和滲透率有顯著異向性，顯然平行未開裂頁理方向具有較高之滲透性; (10)根據E和e的應力相依性回歸函數，可描述應力作用下之 E - e 關係。若使用既有力學內寬閉合曲線推估節理受應力作用時之水力行為，本研究建議使用∆E"-" e關係進行水力耦合分析，避免由於基於ND方法的初始內寬估計而導致的誤差。本研究試驗結果顯示，對於光滑的節理而言，隨著e的降低，E/e呈下降趨勢，與現有的 (E/e)-e 關係矛盾。;Fluid flow through rock masses is a critical issue in rock engineering and geoscience in general, from shallow to great depths. The hydraulic aperture (e) of a single joint under stress is a key variable for simulating the fluid flow through stressed rock masses. Because prediction models for the mechanical aperture (E) of different rock joints under different normal stresses are available, the hydraulic aperture at different depths can be readily estimated using numerous E"-" e relations. However, experimental hydromechanical studies frequently use the normal displacement method (ND method) for determining the mechanical aperture, for which the initial aperture needs to be “estimated”. This uncertainty can propagate to the E"-" e relation. In this study, we conducted high-quality laboratory measurements of mechanical/hydraulic apertures of saw-cut, polished aluminum samples, saw-cut and foliated slate samples which are comparable to smooth rock joints, using the YOKO 2 system under confining stresses from 3 to 120 MPa. Moreover, a novel pulse-decay-balance (PDB) method was proposed to simultaneously measure e and E under stress. The YOKO2 system was modified into a closed system to measure the e and E of saw-cut and foliated slate samples under a confining (normal) stress of up to 60 MPa. The hydraulic aperture was determined based on analysis of the pressure decay curve, and the mechanical aperture was determined based on the joint volume measurement (JV method) by determining the balance pressure.
This study is divided into different parts: (1) e and E measurements of saw-cut smooth aluminum samples with an identical joint surface using steady-state and joint volume method, stress-dependent e and E fit well using a hyperbolic function; (2) A proposed novel PDB method is to measure simultaneously e and E of saw-cut and foliated slate samples, stress-dependent e and E fit well using a hyperbolic function; (3) Influences of measurement and analysis methods on rock apertures determination. We measured the mechanical aperture directly from the joint volume (JV method); this method differs from the widely adopted ND method for measuring joint closure. The experimental results show that the estimation uncertainty of initial aperture, which is required for converting the joint closure curves into mechanical aperture, reduces the reliability of the existing E"-" e relations. (4) When the JV method is used to reduce the influence of initial aperture estimation, it is important to note that the contribution of the matrix pore volume of intact rock to the mechanical aperture measurement is not negligible even when the porosity of the matrix is less than 0.1%. Contrary, the matrix permeability of impermeable rock is negligible for laboratory measurements; (5) Neglecting the quadratic Forchheimer term leads to an underestimation of hydraulic aperture; (6) The hydraulic aperture estimated using the proposed method was comparable to that measured in steady-state tests; (7) The hydraulic apertures of the saw-cut and foliated slate samples estimated using the simplified and general analytical solutions were in good agreement, especially for smooth joints under high normal stress. However, the error in the hydraulic aperture estimation, induced by neglecting the specific storage of the rock joint, is non-negligible for rough rock joints under low normal stress; (8) The measurable hydraulic aperture e via the close system—YOKO2 is several to several tens microns. Although the measurable mechanical aperture E is below 1 micron, the best measurement range of E is roughly 1,000 to 10,000 microns. To harmonize the optimum measurement range of hydraulic and mechanical apertures, using a typical sample size for a conventional triaxial test is suggested; (9) The effect of anisotropic behavior and open foliated joint on the matrix porosity and permeability of intact slate samples is significant; (10) A regression function based on the stress-dependent E and e fitted well with the experimental data to describe the E-e relationship. Our testing results, which show a decreasing trend in the E/e ratio with decreasing e, contradict the existing (E/e)-e relation, at least for smooth joints. Using ∆E"-" e relations for hydromechanical coupling analysis is suggested to avoid errors due to the initial aperture estimation based on the ND method. |
| Appears in Collections: | [Graduate Institute of Applied Geology] Electronic Thesis & Dissertation
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