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Recession of Limestone Clifis in Ryukyu Islands

琉球群岛石灰岩悬崖的退缩

基本信息

批准号：
14580103
负责人：
MAEKADO Akira
金额：
$ 2.18万
依托单位：
University of the Ryukyus
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

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.

从动力学的角度研究了琉球石灰岩海岸悬崖的后退问题。选择冲绳-硫马岛、宫古岛和基凯岛的几个岩质海岸作为调查区域。现场测量了悬崖高度、凹槽深度、落块长度和岩体中的纵波速度。悬崖高度为2~23m，缺口深度为2~9m，块体长度为4~13m。通过室内试验对悬崖材料的物理力学性能进行了测试。随着试件尺寸的增大，岩石强度急剧下降，即琉球石灰岩在岩石强度上具有尺度效应。结合室内尺度效应导致的强度折减结果和室内试验和现场试验的纵波速度结果，推导出了岩体强度的估算公式。采用忽略尺度效应的岩体强度进行稳定性分析，不能很好地解释悬崖破坏。考虑悬崖后张拉裂缝的影响，推导了一个新的稳定性分析方程。将估算的岩体强度和悬崖材料的容重代入方程，得到了悬崖高度和临界缺口深度关系中的临界稳定线。结果表明，目前的悬崖剖面数据绘制在稳定区，而崩塌块体的长度和宽度绘制在临界线上。由此得出结论：考虑岩体强度和拉裂的梁破坏类型分析将为预测琉球石灰岩悬崖的临界缺口深度提供一个有用的框架。