Lithological controls on hydrological processes that trigger shallow landslides: Observations from granite and hornfels hillslopes in Hiroshima, Japan
Lithological controls on hydrological processes that trigger shallow landslides: Observations from granite and hornfels hillslopes in Hiroshima, Japan
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DOI：
10.1016/j.catena.2019.04.010
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发表时间：
2019-09
期刊：
影响因子：
6.2
通讯作者：
Takuma Watakabe;Y. Matsushi
中科院分区：
文献类型：
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作者：
Takuma Watakabe;Y. Matsushi
滑坡过程的全面理解是解释浅滑坡的空间分布和降雨阈值触发滑坡在不同的基岩条件下的关键。在这里，我们讨论了观察到的浅滑坡机制相邻的花岗岩和角岩山坡在北方广岛市，日本西部。浅层地下材料的厚度、结构和岩土性质通过实地调查和实验室实验进行了表征。利用张力计监测了降雨入渗引起的土层孔隙水压力响应。在花岗岩山坡上，雨水从近地表高渗透性的桑迪土快速渗透到深层低渗透性的腐泥土中，而腐泥土的有限蓄水能力导致了从土层底部向上延伸的饱和带的发展。花岗岩坡面上的无粘性土，在上部软弱层与下部坚硬层之间的边界上，当高位水位从下伏腐岩边界上升时，当该边界经受弱的正孔隙流体压力时，可沿该边界沿着滑动。相反，角岩山坡上覆盖着粘性土，渗透性随深度而降低，这有助于形成一个栖息在较低的土壤层以上的地下水体。当潜在滑动面上存在较大的正压力时，上部土层可沿着两土层间的水力机械不连续面滑动。这些结果表明，下伏基岩岩性控制的地下结构，形状的山坡材料的水力和力学性能，以及它们的地下水文过程，这反过来又影响潜在的浅层滑坡。
A comprehensive understanding of landslide processes is critical in explaining the spatial distribution of shallow landslides and rainfall thresholds for triggering landslides under different bedrock conditions. Here we discuss the observed shallow landslide mechanisms on adjacent granite and hornfels hillslopes in northern Hiroshima City, western Japan. The thickness, structure, and geotechnical properties of the shallow subsurface materials were characterized via field-based surveys and laboratory experiments. The observed pore-water pressure responses in the soil layer due to rainfall infiltration were monitored using tensiometers. In the granite hillslopes, the rapid percolation of rainwater from the near-surface high-permeability sandy soil to the low-permeability saprolite at depth and the limited water storage capacity of the saprolite led to the development of a saturated zone that extended upward from the base of the soil layer. The cohesionless soils in the granite hillslopes can slip along the boundary between the weak upper layer and stiff lower layer once this boundary experiences weak positive pore-fluid pressure as the perched water table rises from the underlying saprolite boundary. Conversely, the hornfels hillslopes are covered by cohesive soils in which permeability decreases with depth, which contributes to the formation of a perched groundwater body above the lower soil layer. When a large positive pressure acts on the potential sliding surface, the upper soil layer can slip along the hydraulic and mechanical discontinuity between two soil layers in the hornfels hillslopes. These results indicate that the underlying bedrock lithology controls the subsurface structures that shape the hydraulic and mechanical properties of the hillslope materials, as well as their subsurface hydrological processes, which in turn influence the potential for shallow landslides.