Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XVIII, No.3


Microfracture in Pebbles of the Utaro Conglomerate, Hokkaido Part I : Observation under Scanning Electron Microscope

Uda, Tsuyoshi

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The axial-ratio of limestone and granite pebbles in the Utaro Conglomerate differs from the result of three-axial compressive tests. Observation of the fracture surface by S.E.M. revealed that the intragranular and intergranular normal ruptures develop in the limestone pebbles. On the contrary, in the granite pebbles many types of fracture are observed. If the difference of their initial states is negligible, the propaganda of fracture can be discussed by assuming the condition under which the applied stress remains constant. In the case of limestone, the apicies of fractures look stair-like form due to generation of punched dislocation. This phenomenon probably indicates that the critical strength is smaller than E/10 and plastic relaxation is generated at the apicies of fractures. On the contrary, the granite pebble behaves as a brittle (i.e. σc ≫ E/10), and is deformed elastically during stress acted. Therefore, the fractures are well developed and megascopical axial-ratio is increased.