Study on the Roughness Variation of Rock Joints during Shearing
Date Issued
2010
Date
2010
Author(s)
Pung, Shih-Jung
Abstract
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.
Subjects
PFT
roughness
micro- mechanics model
Type
thesis
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