| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 100 === Plucking is often the dominant mechanism of bedrock erosion when the rock riverbed is composed of heavily jointed rock masses. This thesis made use of particle flow simulation to model the bedrock incision by plucking. Through numerical simulation, the thesis looked into the microscopic features of the plucking mechanism and explored the important factors that may affect the kinematics and the kinetics of rock-block plucking in block scale.
This study first simulated the direct shear on modeled weak plane to properly model the mechanical behavior on a discontinuity. Through simulation, it was validated that the peak strength increases with the increase in rock-bridge cohesion, whereas the post-peak frictional resistance increases with the rise in the frictional coefficient of the weak plane. The role of rock bridges tends to be more important as the area ratio of rock bridge increases.
Subsequently, the study simulated the plucking behavior of jointed rock masses with virtual specimens composed of arranged blocks. Plucking simulation of single block and multiple blocks, respectively, were conducted. From the simulation of single block, it appears the uplift speed is negatively correlated with the following weak-plane characteristics: the area ratio and bond strength of rock bridges as well as the cohesion and the shear stiffness of weak plane. For the influence of the uplift force, the uplift speed increases as the mean value of pressure fluctuation increases. The plucking simulation of multiple blocks allows concurrent movements of adjacent blocks. The effects of the distribution of rock bridges and the orientation of joints were examined through simulation. It is shown that, for multiple blocks, there is a key block on the top layer to control the plucking of the jointed rock masses. Once the key block is removed, the uplift speed of other blocks will suddenly increase.
On the basis of the simulated results, this study further proposed a simplified approach for the estimation of scouring depth by plucking during a specific flood event. For conservative concern, plucking speed was estimated using the results of single block plucking simulation. An example for applying the proposed simplified approach was also presented.
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