- 學位論文
剪力作用下岩石節理面粗糙度變化之研究
Study on the Roughness Variation of Rock Joints during Shearing
摘要
岩石節理面的力學性質掌握著節理岩體的工程性質，而粗糙特徵又是影響節理面力學行為的主要因素，其中剪力作用下的節理粗糙的複雜特性，至今仍為岩石力學主要的探討課題。本研究選取Barton(1977)之兩個標準剖面(JRC14~16及18~20)作為研究探討對象，施以正應力為0.5MPa、1.0MPa及1.5MPa之條件，進行漸進式直接剪力試驗(PFT)分析。試驗之剪動位移量則依正規化剪力曲線選取四個代表剪動階段(定為0.3倍、0.6倍、1倍及2倍尖峰剪位移)，作為節瘤漸進式破壞發生之探討基準，藉由各剪位移階段的試體破壞表徵，觀察節瘤受剪發生漸進破壞特性與節理力學行為間之相關性。並利用快速傅立葉轉換(FFT)估計粗糙度JRC值及觀察影響力學行為之粗糙特徵。 本研究更利用節理面微觀力學組成模式，針對上述標準剖面進行對照組之模擬分析，藉由各剪位移階段所得之節瘤破壞模式、位置及規模，與直剪試驗結果相互比較印證，以確認節理粗糙特性在受剪過程中變化的趨勢，可更深入的瞭解節理面力學行為與節瘤漸進式破壞的關係。最後，取部份試驗結果利用數位影像相關係數法(DIC)量測，研究DIC之量測準確性。 本研究獲致成果為:節理面於剪動初期之剪力強度由少量底長小於5mm的細小高傾角節瘤剪壞，及主要節瘤表面擦痕與接觸界面摩擦力所一起提供，於尖峰剪位移之剪力強度主要由底長10~20 mm之低傾角節瘤剪斷破壞提供，峰後節理面剪力強度主要是由主要節瘤與高程相近之節瘤剪斷破壞所提供；快速傅立葉(FFT)估計JRC值不受水平取點間距影響，但對於細微節瘤變化較不敏感；模式分析部分，剪力峰前行為、尖峰剪力強度及節瘤強度之影響可透過節理剪向勁度、材料基本摩擦角及完整岩材三軸強度控制；透過交叉相關係數比較得數位影像相關係數法(DIC)為一良好之量測剖面工具。
並列摘要
The mechanical properties of rock joint control the engineering properties of rock mass, while roughness characteristics mainly dominate the mechanical properties of rock joint. Thus, the complex behavior of rock joint roughness under shearing remains an important branch among the research topics in rock mechanics. In this research, two standard profiles proposed by Barton (1977), with JRC 14~16 and 18~20, are selected as the modeling profiles. Gypsum specimens with standard profiles are used to conduct proceeding Progressive Failure Test (PFT) with three different normal stress, 0.5MPa, 1.0MPa and 1.5MPa. Four shear displacement stages, 0.3, 0.6, 1.0, 2.0 times the peak shear displacement, are selected from normalized shear force-displacement curve as the basis to understand progressive asperities failure. With the failure patterns under different shear displacement stages, the correlation between asperity failure characteristics and joint mechanical behavior can be observed. Furthermore, Fast Fourier Transform (FFT) is used to estimate JRC and to observe roughness properties. In order to confirm experimental results and to verify joint roughness properties during shear test, a micro-mechanical constitutive model is used to analyze the roughness variation during shearing. Finally, part of the gypsum specimens were measured by Digital Image Correlation Method (DIC) to discuss the accuracy of DIC. The results showed that: at the beginning of shearing, shear strength is provided by high-diped asperities with length less than 5 mm and friction between contact surface and major asperities. At peak shear displacement, shear strength is provided by low-diped asperities with length between 10~20 mm. After peak, shear strength is provided by major asperities. The estimation of JRC by FFT would not be influenced by horizontal sampling interval; however, it is insensitive with the variation of minor asperities. Micro-mechanical analysis proved that the shear strength of rock joint can be controlled by joint shear stiffness, basic friction angle and intact rock tri-axial strength. By comparing with experiment results, DIC is found to be a good method for profile measurement.