| Project/Area Number |
14580103
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
自然地理学
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| Research Institution | University of the Ryukyus |
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Principal Investigator |
MAEKADO Akira University of the Ryukyus, Faculty of Law and Letters, Professor, 法文学部, 教授 (60190287)
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| Co-Investigator(Kenkyū-buntansha) |
HIROSE Takashi University of the Ryukyus, Faculty of Law and Letters, Associate Professor, 法文学部, 助教授 (40305181)
MATSUKURA Yukinori University of Tsukuba, Institute of Geoscience, Professor, 大学院・生命環境科学研究科, 教授 (80107341)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2004: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2002: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | Limestone / Cliff / Failure recession / Rock property / Crack / Stability analysis / Notch / Scale effect / 琉球石灰岩 / 海食崖 / テンションクラック |
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| Research Abstract |
Recession of coastal cliffs made of Ryukyu Limestone was studied from the dynamic viewpoint. Several rocky coasts of Okinawa-jima, Miyako-jima and Kikai-jima were selected as the investigated areas. Field measurements were carried out for the cliff height, the depth of notches, the length of fallen blocks and longitudinal wave velocity in rock mass. The cliff height, notch depth and block length range from 2-23 m, 2-9 m and 4-13 m, respectively. Physical and mechanical properties of the cliff material were measured through the laboratory tests. The rock strength drastically decreases with increasing size of specimen, i.e., Ryukyu Limestone has the scale effects in rock strength. Combining the laboratory results of strength reduction due to scale effect and the results of the longitudinal wave velocity obtained from both laboratory and field tests, an equation was derived for estimating of the rock mass strength.
Cliff instability was analyzed using a beam analysis model. The stability analysis using the strength of rock mass ignoring scale effects could not well explain cliff failures. Considering tension cracks behind cliff, a new equation for stability analysis was derived. Substituting the estimated rock mass strength and unit weight of cliff material into the equation, we obtain the critical stability lines in cliff height and critical notch depth relationships. Results show that the data from the present cliff profile was plotted in the stable area, while the length and breadth of fallen blocks was plotted on the critical lines. This leads to the conclusion that the analysis of beam failure type, which takes account of the rock mass strength and tension crack, would provide a useful framework for predicting the critical notch depth of cliff made of Ryukyu Limestone.
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