Fracturing Process and Durability Evaluation of Rocks Subjected to Freezing-and-Thawing Cycles

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Other Title
  • 凍結融解作用を受ける岩石の破壊プロセスと耐久性の評価
  • トウケツ ユウカイ サヨウ オ ウケル ガンセキ ノ ハカイ プロセス ト タイキュウセイ ノ ヒョウカ

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Durability evaluation of rocks subjected to freezing-and-thawing is important for stability assessment of a rock fill dam as well as rock slopes, especially in cold weather regions. In this study, freezing-and-thawing tests up to 300 cycles were carried out on twelve kinds of rock samples in order to characterize fracture propagation by freezing-and-thawing and evaluate the durability, and fracture propagation was observed. The fracturing process was characterized by macroscopic observation by digital camera and changes in physical properties. Fracture initiation and propagation in the specimen were also observed by using X-ray CT. It was found that the fracturing process depends on the rock type. For rocks which possess preferred orientation of pre-existing fractures and anisotropy of tensile strength, only one fracture propagated dominantly and split the rock sample in half. On the other hand, for isotropic rock, propagation of several fractures occurred and rock samples were split into several parts. Additionally, spalling continuously progressed once the loss of weight exceeded 5% for isotropic rocks because fractures had developed throughout the specimen. This result indicates that freezing-and-thawing cycles at 5% weight loss is assumed to be the spalling initiation. Therefore, we can conclude that the number of freezing-and-thawing cycles to the spalling initiation is the important indicator of the durability evaluation. It was also pointed out that both supply capacity of water to the crack tip and crack growth resistance affect the durability, because the tensile strength divided by the percentage of water absorption is in good correlation with the number of cycles to the spalling initiation. It is concluded that the durability can be easily evaluated by both tensile strength and the percentage of water absorption.

Journal

  • Journal of MMIJ

    Journal of MMIJ 127 (3), 117-126, 2011

    The Mining and Materials Processing Institute of Japan

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