| Summary: | 碩士 === 淡江大學 === 土木工程學系 === 89 === The shearing process of the joints always results in the failure of the joints, specifically in the two dimensions: the scale effect and the progressive failure. First, the phenomenon of the scale effect is mainly affected by the size of the joint area. Thus, a small joint area than that of a large joint area causes a much larger real contact area. As soon as the real contact area becomes much larger, the shear stress of the joints increases. Secondly, the phenomenon of progressive failure relates to the distribution of the stress. As the asperities that are early destroyed transfer the stress to other asperities, consequently, the asperities that are transferred the stress to later come to fail. The sequence of the asperities destruction is caused by the two factors----the “angle” and the “position” of the asperities.
The purpose of the research is to understand the failure behavior of the joints by analyzing the distribution of the stress and the transfer in the joints. The design of the research is to measure the changes of stress in the joints on the condition that the sheer stress and the sheer displacement increase and the contact area decreases. The measurement used in the research is to attach the strain gages to the sides of different kinds of teeth profiles.
The outcomes of the research are: (1) The factors affect the progressive failure are the angle and the position of the tooth, while the factor of angle is dominant of the two, (2) The transfer behavior of local normal stress in the joint profile of the two teeth is the basic model of the multiple teeth, (3) The maximum of the local normal strength is as the same value as that of the unconfined compression strength. And the maximum of the local normal strength happens while the sheer stress reaches its peak at the same time. It is proved that the local strength of rock materials controls the strength of the whole joint, (4) As the complex profile is sheared by different directions, the stress is first taken by the tooth of higher angle and then the stress is transferred to the tooth of lower angle. There are two conclusions are made from the above finding: first, the tooth of higher angle controls the peak of the shear strength; second, the transfer of the stress and the failure of the teeth develop in order and the development of stress in two kinds of angle teeth are independent.
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