Triggering and motion of landslides
Triggering and motion of landslides
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DOI：
10.1680/jgeot.20.rl.001
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发表时间：
2021-01-01
期刊：
影响因子：
5.8
通讯作者：
Alonso, Eduardo E.
中科院分区：
文献类型：
--
作者：
Alonso, Eduardo E.
本文分析了一类滑坡的动力特性，其特征是具有明确的剪切应变积累的破坏面。该主题超越了安全系数和静态分析的常见概念，并讨论了一旦失去稳定性时识别速度和跳动的程序。三个最初的历史案例有助于强调预测失败后运动的相关性。本文讨论的这些案例和其他一些案例有助于将理论发展与其在实践中的相关性联系起来。以下滑坡得到了论文的关注：潘帕内拉、科尔特斯、阿兹纳尔科勒、瓦尔塞布雷、塞尔本、瓦扬特和卡内莱斯。现有的出版物对所有这些都进行了详细的描述。这些滑坡说明了以下现象：爬行运动、首次破坏、快速滑动以及从缓慢运动到非常快速运动的过渡。这些现象存在于本文的概念和组织中。简单的几何图形（平面，双块）有助于描述基本物理，但也能够提供有用的解决方案和深刻的理解。在第二阶段，简单滑动情况演变为连续体分析。物质点法（MPM）提供了接近任意几何形状的可能性，并消除了简单情况下的主要限制假设，即对破坏机制及其后续传播的“先验”知识。两个有充分记录的脆性、高塑性、超固结粘土的渐进破坏案例（Aznalcollar和Selborne）为检验MPM分析正确预测剪切面内部发展和观察到的波动的能力提供了有用的数据。该方法还提供了关于从本质上的“静态”行为到加速位移的转变的信息。受Selborne案例启发的敏感性分析得出了跳动和土壤脆性之间有趣的关系。速率效应对摩擦角的影响解释了滑坡的蠕变行为。在孔隙水压力的时间历史下，Vallcebre滑动速度的变化为简单的建模方法提供了验证。然而，摩擦定律并不能很容易地解释在像瓦永特这样的滑坡中观察到的突然加速度。先前的研究解释了在一些滑坡中观察到的快速加速和快速运动，这些研究依赖于滑动表面的热致孔隙压力。进一步的工作为Vajont滑坡引入了双楔体，强调了剪切带厚度的相关性，特别是土壤渗透性。将所涉及的热-水-机械（THM）公式以MPM的方式推广，解决了由于剪切带厚度的网格尺寸控制而产生的不一致结果的困难。解决方案是在描述土壤基质的材料点中嵌入具有合理厚度的剪切带。这种方法成功地再现了已知的vajjont失效后运动。该模型给出了滑动岩体的内剪切、滑动面温升及其瞬态超孔隙压力的估计。最后一节描述了滑坡的蠕动运动与其最终演变成快速现象之间的密切关系。一个简单的平面滑动提供了一组控制相互作用的无量纲参数。应变率对摩擦的影响解释了蠕变部分的问题。本文描述了用MPM公式求解任意几何的一种推广方法。Canelles滑坡有助于讨论基于蠕变的存在与否和公式的THM物理及其可能的组合的预测的优点和局限性。
The paper analyses the dynamic behaviour of a class of landslides characterised by a well-defined failure surface where shear strains accumulate. The subject goes beyond the common concepts of safety factor and static analysis, and discusses procedures to identify the velocity and runout, once stability is lost. Three initial case histories serve to highlight the relevance of predicting the motion after failure. These cases and a few others discussed in the paper help to connect the theoretical developments with their relevance in practice. The following landslides receive attention in the paper: Pampaneira, Cortes, Aznalcollar, Vallcebre, Selborne, Vajont and Canelles. Existing publications describe all of them in some detail. These landslides illustrate the following phenomena: creeping motion, first-time failures, rapid sliding and the transition from slow to very rapid motion. These phenomena are present in the concept and organisation of the paper. Simple geometries (planar, double block) facilitate the description of the basic physics but are also capable of delivering useful solutions and deep understanding. In a second stage, the simple sliding cases evolve into continuum analysis. The material point method (MPM) offered the possibilities of approaching arbitrary geometries and removed a main limiting assumption of simple cases, namely the 'a priori' knowledge of the failure mechanism and its subsequent propagation. Two well-documented cases of progressive failure in brittle, high-plasticity, overconsolidated clays (Aznalcollar and Selborne) provided useful data to check the capabilities of the MPM analysis to predict correctly the internal development of shearing surfaces and the observed runout. The method also provides information regarding the transition from an essentially 'static' behaviour to an accelerated displacement. A sensitivity analysis, inspired by the Selborne case, resulted in an interesting relationship between runout and soil brittleness. Rate effects on friction angle explain the creeping behaviour of landslides. Changing velocities of Vallcebre slide under a time history of pore water pressures provided a validation exercise for a simple modelling approach. However, friction laws do not easily explain the sudden acceleration observed in landslides such as Vajont. Previous work to explain the rapid acceleration and fast motion observed in some landslides rely on heat-induced pore pressurisation of the sliding surface. Further work introducing a double wedge for Vajont landslide stressed the relevance of shear band thickness and, in particular, the soil permeability. A generalisation of the involved thermo-hydro-mechanical (THM) formulation, by way of MPM, met the difficulty of solving the inconsistent results deriving from the mesh-size control of the shear band thickness. The solution was to embed shear bands, with a reasonable thickness, in the material points describing the soil matrix. This approach successfully reproduced the known Vajont after-failure motion. The model provided estimations of the internal shearing of the sliding rock mass, the temperature increase of the sliding surface and its transient excess pore pressures. A final section describes the close relationship between the creeping motion of a landslide and its eventual evolution towards a rapid phenomenon. A simple planar slide provided a set of dimensionless parameters governing the interaction. Strain rate effects on friction explained the creeping part of the problem.The paper describes a generalised approach to arbitrary geometries by means of MPM formulation.Canelles landslide was useful to discuss the merits and limitations of predictions based on the absence or presence of creeping and THM physics of the formulation and their possible combinations.