Some landslides around the world that have low-angle failure planes show exceptionally poor mechanical properties. In some cases, an extraordinarily pure clay layer has been detected on the rupture surface. In this work, a complex landslide, the so-called Diezma landslide, is investigated in a low- to moderate-relief region of Southeast Spain. In this landslide, movement was concentrated on several surfaces that developed on a centimeter-thick layer of smectite (montmorillonite-beidellite) clay-rich level. Since these clayey levels have a very low permeability, high plasticity, and low friction angle, they control the stability of the entire slide mass. Specifically, the triggering factor of this landslide seems to be linked to the infiltration of water from a karstic aquifer located in the head area. The circulation of water through old failure planes could have promoted the active hydrolysis of marly soils to produce new smectite clay minerals. Here, by using geophysical, mineralogical, and geochemical modelling methods, we reveal that the formation and dissolution of carbonates, sulfates, and clay minerals in the Diezma landslide could explain the elevated concentrations of highly plastic secondary clays in its slip surface. This study may help in the understanding of landslides that show secondary clay layers coinciding to their low-angle failure planes.

中文翻译：

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边坡不稳定性滑面富含粘土层的形成：地下水的作用

世界上一些具有低角度破坏面的滑坡显示出异常差的机械性能。在某些情况下，在破裂面上检测到异常纯的粘土层。在这项工作中，对西班牙东南部低至中度地势地区的复杂滑坡，即所谓的 Diezma 滑坡进行了调查。在这次滑坡中，运动集中在几厘米厚的蒙脱石（蒙脱石-贝得石）富粘土层上形成的表面。由于这些粘土层具有非常低的渗透性、高塑性和低摩擦角，因此它们控制着整个滑动体的稳定性。具体来说，这次滑坡的触发因素似乎与水从位于头部区域的岩溶含水层渗入有关。水通过旧的破坏面循环可能促进了泥灰质土壤的活性水解，以产生新的蒙脱石粘土矿物。在这里，通过使用地球物理、矿物学和地球化学建模方法，我们揭示了 Diezma 滑坡中碳酸盐、硫酸盐和粘土矿物的形成和溶解可以解释滑坡表面高塑性次生粘土浓度升高的原因。这项研究可能有助于理解显示次生粘土层与其低角度破坏面重合的滑坡。Diezma 滑坡中的粘土矿物和粘土矿物可以解释其滑坡表面高塑性次生粘土浓度升高的原因。这项研究可能有助于理解显示次生粘土层与其低角度破坏面重合的滑坡。Diezma 滑坡中的粘土矿物和粘土矿物可以解释其滑坡表面高塑性次生粘土浓度升高的原因。这项研究可能有助于理解显示次生粘土层与其低角度破坏面重合的滑坡。