Geo-and hydro-mechanical evaluation of slope failure induced by torrential rains in Northern-Kyushu area, July 2009
Geo-and hydro-mechanical evaluation of slope failure induced by torrential rains in Northern-Kyushu area, July 2009
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北九州地区暴雨引发的边坡破坏的地质和水力评估，2009年7月
DOI：
10.3208/sandf.51.575
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发表时间：
2011
影响因子：
3.7
通讯作者：
Hidefumi Sato
中科院分区：
文献类型：
--
作者：
K. Kasama;Yujing Jiang;A. Hiro;N. Yasufuku;Hidefumi Sato
摘要2009年7月中旬，日本中部和北方九州地区遭遇强降雨，引发了多起滑坡、泥石流等地质灾害。山口县和福冈县发生了一些斜坡崩塌和泥石流，对人的生命和基础设施造成了广泛的破坏。日本福冈县的佐佐里町和福冈町发生的滑坡和泥石流是最严重的地质灾害之一。本文总结了福冈县地质灾害现场的岩土工程勘察结果。岩土工程调查包括确定一系列的粒度分布，一致性限制，并进行直接盒剪切试验，在六个灾害现场收集的塌陷土壤。通过对崩塌土的降雨、地形、地质和强度特性的分析，探讨了泥石流诱发边坡失稳的机理。结合边坡变形和稳定性分析以及非饱和-饱和渗流分析，探讨边坡破坏机理。主要研究结果如下：总结了崩塌土的颗粒级配、塑限和液限等物理性质，并与文献中其他破坏边坡的结果进行了比较。结果表明，该塌陷土具有颗粒均匀（均匀系数>50）、强风化（烧失量>5%）的特征，但液限和塑性指标无明显变化。天然含水量的崩塌土的原始抗剪强度较大，不会发生边坡破坏，因为抗剪强度中的粘聚力是由非饱和状态下土粒之间的吸力引起的。然而，水渗入土壤会导致抗剪强度急剧下降，这主要是由于土壤饱和导致粘聚力下降（失去吸力）造成的。此外，剪切过程中的排水/不排水条件对剪切强度也很敏感。例如，水渗透和剪切过程中的恒定体积造成约30%的剪切强度降低Fukuchi-machi和Sasaguri-machi土样。因此，渗水引起的粘聚强度降低和边坡的低渗透性是引发地质灾害的参数。根据边坡变形的结果和考虑水压力和粘聚力变化的稳定性分析，模拟了福知町的地质灾害，可以合理地假设，坡顶附近的浅层破坏是由于约100 mm/h的暴雨引发泥石流造成的。
ABSTRACT Torrential rainfall in mid-July 2009 triggered numerous geodisasters such as slope failure and debris flow in Chugoku and Northern Kyushu areas of Japan. A number of slope failures and debris flows occurred in Yamaguchi and Fukuoka prefectures resulting in extensive damage to human life and infrastructure. One of the most serious geodisasters included a slope failure followed by debris flow at Sasaguri-machi and Fukuchi-machi, Fukuoka prefecture, Japan. This paper summarizes the results of geotechnical investigations on the geodisaster sites in Fukuoka prefecture. The geotechnical investigation included determining a series of grain size distributions, consistency limits and conducting direct box shear tests for collapsed soils collected at six disaster sites. The generation mechanisms of slope failure followed by debris flow were also investigated by analyzing the precipitation, topography, geology, and strength properties of the collapsed soils. Moreover, slope deformation and stability analyses were coupled with an unsaturated-saturated seepage analysis to investigate the slope failure mechanism. The main findings from the study are summarized as: The physical properties, such as the grain size distribution, the plastic limit and liquid limit of collapsed soils, are summarized and compared with the results of other failure slopes in the literature. The collapsed soil was characterized as being a well grained soil (the uniformity coefficient >50) and highly weathered (the ignition loss >5%), however, with regard to the liquid limit and plastic index, there were no remarkable findings. The original shear strength for collapsed soils with natural water content is relatively large and slope failure doesn't occur because the cohesion in the shear strength is induced by a suction force between the soil particles under unsaturated condition. However, water seepage into the soil induces a drastic decrease in the shear strength, which is mainly caused by a decrease in cohesion (losing suction) resulting from soil saturation. In addition, the drained/undrained condition in the shear process is also sensitive to shear strength. For example, both water seepage and the shear process with constant volume cause an approximate 30% reduction in shear strength for Fukuchi-machi and Sasaguri-machi soil samples. Therefore, the reduction of cohesive strength due to water seepage and the low permeability of the slope are the parameters which trigger geodisaster. Based on the results of slope deformation and a stability analyses which took the change in water pressure and cohesive strength into account, the geodisaster at Fukuchi-machi was simulated, it is reasonable to assume that the shallow failure near the top of slope occurred due to torrential precipitation of about 100 mm per hour which triggered a debris flow.