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研究生： 黎慶
Le Hoang Khanh
論文名稱： 以直剪試驗及數值模型探討節理岩體之剪力強度與微觀力學機制
The relationship of shear strengths and micromechanical behaviors of jointed specimens by direct shear tests and discrete element models
指導教授： 黃文昭
口試委員:
學位類別： 博士
Doctor
系所名稱： 工學院 - 土木工程學系
Department of Civil Engineering
論文出版年： 2021
畢業學年度： 109
語文別： 英文
論文頁數： 229
中文關鍵詞： 直剪試驗 、2D-DEM數值模型 、人造節理 、微觀力學行為 、殘餘剪切強度
外文關鍵詞： direct shear test, 2D-DEM model, artificial joint, micromechanical behavior, residual shear strength
相關次數： 點閱：11  下載：0 
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    • 節理與層面等不連續面之岩體抗剪強度為岩土工程評估岩質邊坡和隧道穩定性之關鍵因素。Barton公式是評估岩石節理剪切強度的最廣泛使用的方法之一。在方程式中，節理粗糙度係數 (JRC)為影響剪切強度之關鍵因子，係因其為控制不連續面粗糙度之重要參數。
    在先前的研究中顯示，藉由Excel以常態分佈可創造特定JRC之剖面，並據以製作研究所需之人造節理試體進行直剪試驗。
    本研究透過物理試驗和數值模擬（Discrete Element Method,簡稱DEM），對軟和中等強度岩石節理進行了一系列直剪試驗與數值模擬分析，並探討隨機生成 JRC 剖面之力學特性。其中，控制 JRC 值（20、19.6 和 10）的節理粗糙度是藉由 Le (2018)等人提出的 PHV 方法生成。
    首先，物理試驗是以3D列印製作模型，並澆置JRC為19.6之石膏樣本，其無圍壓縮強度為4.42 MPa 比照軟岩。其次，將石膏樣本以光掃描後計算實際 JRC為 16.8。接著，運用2D-DEM採實際JRC建置數值模型，並進行石膏節理不連續面數值模擬。此外，本研究亦使用不同JRC之水泥試體進行直剪試驗與數值模擬，並與石膏試體的測試結果進行比較。其中，水泥試體之控制JRC分別為20、19.6 及 10，其掃描得到實際JRC分別為 10、11 及 2.4，其無圍壓縮強度為37.1 MPa比照中等岩石。

    The shear strength of rock mass containing discontinuities, such as joints and bedding planes, plays an essential role in estimating the stability of a rock slope and tunnels in rock engineering. Barton's formula is one of the most widely used equations for estimating the shear strength of rock joints. The Joint Roughness Coefficient (JRC) in the equation is a crucial parameter of the shear strength because it controls the profile's roughness. In this study, a series of direct shear tests in both laboratory and numerical modeling (through Discrete Element Method, DEM) was conducted for soft and medium strength rock joints to elucidate the mechanical properties of a randomly-generated JRC profile. The joint profile with a given JRC value (20, 19.6, and 10) was generated using the PHV approach proposed by Le et al. (2018). The artificial gypsum specimen (soft rock with UCS=4.42 MPa) with JRC=19.6 was replicated from the 3D-printed joint block in the laboratory. The actual JRC of the joint gypsum specimen was then light-scanned and re-estimated as 16.8. Afterward, 2D-DEM was employed to simulate the joint gypsum model with the same actual JRC as in the laboratory. Besides, a series of artificial cement specimens with different JRC were also cast using a cement mixture (medium rock with UCS=37.1 MPa) for comparison with the test results of gypsum specimens. The actual JRC values of joint profiles of artificial cement specimens (with given JRCs of 20, 19.6, and 10) are recalculated as 10, 11, and 2.4, respectively. The DS simulation on cement specimens was also performed.

    摘要 i Abstract ii DECLARATION iii List of Tables vii List of Figures ix Explaination of symbols xix Chapter I Introduction 1 1.1 Overview 1 1.2 Content of the dissertation 5 Chapter II Literature review 6 2.1 Research background 6 2.2 Importance of peak and residual shear strength 23 2.3 Review of current methods for JRC estimation 30 2.3.1 JRC estimation based on Barton’s standard profiles 30 2.3.2 JRC estimation based on the root mean square value Z2 32 2.3.3 JRC estimation based on the fitting parameter C 33 2.3.4 JRC estimation based on the fractal dimension parameter D 36 2.3.5 JRC estimation based on the PHV method 38 2.4 Review of 3D-printing technology 47 Chapter III Methodology 49 3.1 Material and test apparatus 49 3.1.1 Material 49 3.1.2 UCS equipment 52 3.1.3 Application of 3D-printing technology and PHV method 56 3.1.4 3D scanner 62 3.1.5 DS equipment 71 3.2 Performance of Particle Flow Code (PFC2D version 5.0) 78 3.2.1 Introduction 78 3.2.2 Constitutive models used in PFC2D in this study 79 3.2.3 Formation of UCS, DS models, and required model parameters 82 3.2.4 Model calibration 90 3.3 Plans for performing lab tests and numerical simulations 94 Chapter IV Direct shear test results and discussion 98 4.1 Direct shear results of artificial gypsum specimens 98 4.2 Direct shear result of artificial cement specimens 102 4.3 Comparison in profile change of the joint surface of artificial specimens after the test 110 4.3.1 Profile change of the joint surface of artificial gypsum specimens 110 4.3.2 Profile change of the joint surface of artificial cement specimens 115 4.4 Influence of the JRC on the shear strength of jointed cement specimens 124 4.5 Influence of the UCS on the behavior of the stress-displacement curve and failure mechanism of the jointed specimens 127 Chapter V Numerical simulation results 129 5.1 Results of numerical simulation on gypsum specimens and comparison with the lab test result 129 5.2 Results of numerical simulation on cement specimens and comparison with the lab test result 137 5.3 Exploring the micromechanical behavior of the joint model 154 5.3.1 Distribution of contact forces of DS models during shearing 154 5.3.2 Development of fractures of DS models during shearing 168 Chapter VI Residual shear strength of artificial joint specimens 181 6.1 Calculation of the mobilized JRC after the test 181 6.2 Estimation of the mobilized friction angle 184 6.3 Estimation of the residual shear strength 187 6.4 Estimation of residual shear strength for gypsum specimens using the empirical formula in this study 188 6.5 Estimation of residual shear strength for Liu et al.’s test data (2020) using the empirical formula in this study 190 Chapter VII Conclusions and Suggestions 193 7.1 Conclusions 193 7.2 Suggestions 199 References 200

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