Vadose Zone Thickness Limits Pore‐Fluid Pressure Rise in a Large, Slow‐Moving Earthflow
Vadose Zone Thickness Limits Pore‐Fluid Pressure Rise in a Large, Slow‐Moving Earthflow
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DOI：
10.1029/2021jf006415
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发表时间：
2022-06
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影响因子：
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通讯作者：
C. R. Murphy;N. Finnegan;F. K. J. Oberle
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文献类型：
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作者：
C. R. Murphy;N. Finnegan;F. K. J. Oberle
水文滑坡的发生率和发生时间是降水模式、材料特性、地形和地下水水文学的复杂函数。然而，在最简单的形式中，当地下孔隙压力增长到足够大以超过莫尔-库仑破坏准则时，斜坡破坏。滑坡中孔隙压力上升的能力部分取决于地下水位以上非饱和带的厚度，而地下水位本身又取决于风化模式，而风化模式在不同的岩性中应该具有可预测的模式。为了研究这种结构如何影响滑坡行为，我们利用了橡树岭土流的多年降水、孔隙压力和速度记录，该土流是位于美国加州北方方济各混杂岩中的缓慢移动滑坡。结合电阻率层析成像和水力传导性测量，这些数据表明，橡树岭有一个薄的风化剖面，其厚度与加州的其他混杂岩滑坡相当。我们建议，由于固有的薄包气带，混杂景观经历了异常高的地下水位，经常使他们接近运动，但是，增加压力的能力是有限的少量的动态存储。相反，一旦地下水位到达地表，多余的孔隙压力就会通过泉水和饱和地表水流流出。风化模式，水文和变形之间的联系可以解释方济各混杂土流在一个大的降水梯度表现出的行为模式。
The rate and timing of hydrologically forced landslides is a complex function of precipitation patterns, material properties, topography, and groundwater hydrology. In the simplest form, however, slopes fail when subsurface pore pressure grows large enough to exceed the Mohr‐Coulomb failure criterion. The capacity for pore pressure rise in a landslide is determined in part by the thickness of the unsaturated zone above the water table, which itself is set by weathering patterns that should have predictable patterns across different lithologies. To investigate how this structure affects landslide behavior, we exploit a multi‐year record of precipitation, pore pressure, and velocity from Oak Ridge earthflow, a slow‐moving landslide set in Franciscan mélange, northern California, USA. In conjunction with electrical resistivity tomography and hydraulic conductivity measurements, these data show that Oak Ridge has a thin weathered profile that is comparable in thickness to other mélange landslides in California. We propose that due to the inherently thin vadose zone, mélange landscapes experience an unusually high water table that frequently brings them close to movement; however, the capacity to increase stress is limited by the small amount of dynamic storage available. Instead, excess pore pressure is shed via springs and saturation overland flow once the water table reaches the surface. Linkages between weathering patterns, hydrology, and deformation can explain behavior patterns exhibited by Franciscan mélange earthflows across a large precipitation gradient.