Determining grain size distribution of the material composing landslide dams in the Northern Apennines: sampling and processing methods
Determining grain size distribution of the material composing landslide dams in the Northern Apennines: sampling and processing methods
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DOI：
10.1016/s0013-7952(02)00249-1
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发表时间：
2003-04-01
影响因子：
7.4
通讯作者：
Rosati, G
中科院分区：
文献类型：
--
作者：
Casagli, N;Ermini, L;Rosati, G
滑坡坝是一种特殊的天然坝，当土质或岩体到达河道，使其完全或部分堵塞而形成。自1995年以来，佛罗伦萨大学地球科学系一直在进行一个项目，其中包括清点北亚平宁地区的滑坡水坝，目前有60多个案例研究。众所周知，滑坡坝的岩土力学特征与筑坝材料的粒度分布密切相关。其中，粒度对坝体稳定性起着控制作用，影响坝体材料的强度和渗透性。这项工作的主要目的是通过概述可用于粒度评估的可能方法，并显示从北亚平宁地区选择的案例研究中获得的结果，从而有助于滑坡水坝的粒度特征。事实上，尽管它很重要，但很少有定量研究针对确定碎片坝的粒度分布，主要是因为习惯的散装筛分析在处理通常从几十立方米大小的块到微观颗粒的材料时是不切实际的。本文介绍了42个滑坡坝的两种主要抽样方法的应用结果，(a)体积分析和(b)网格数字分析（这里有两种变体）。这些技术使我们能够获得非常相似的碎片材料粗部分的粒度分布，而对于较细的部分则存在一些差异。本文还想强调获得准确粒度数据的重要性，特别是在确定滑坡坝破坏的水文曲线时。许多确定性模型试图通过只考虑累积粒度分布的中位数（D-50）来解决这个问题。然而，在大多数选定的情况下，在频率图中发现了明显的双峰分布，因此第五十百分位（D;()）通常是代表性较小的粒度类别之一。因此，应仔细考虑到这种选择可能具有误导性，因为它不一定有实物证据证明是正确的。(C) 2002 Elsevier Science B.V.版权所有
Landslide dams are a particular kind of natural dam which forms when an earth or rock mass reaches a river channel causing its complete or partial blockage. Since 1995, the Earth Sciences Department of the University of Firenze has been running a project involving the inventory of landslide dams in the Northern Apennines, which currently contains more than 60 case studies. It is known that the geotechnical characterisation of landslide dams is closely related to the grain size distribution of the materials composing the dams. In particular, grain size exerts a control on dam stability, influencing the strength and the permeability of the dam material. The main purpose of this work is to contribute to grain size characterisation of landslide dams by giving an outline of the possible methods that can be used for grain size assessment and showing the results obtained from the case studies selected in the Northern Apennines. Indeed, despite its importance, there are few quantitative studies directed at determining grain size distribution of debris dams, mainly because customary bulk sieve analyses are impractical when dealing with materials often ranging in size from blocks tens of cubic metres in size, to microscopic particles. This paper presents results derived from the application of two main sampling methods on 42 landslide dams, (a) volumetric analysis and (b) grid by number analysis (here presented in two variants). These techniques allow us to obtain very similar grain size distributions for the coarser part of the debris material, while some differences persist for the finer fraction, The paper would also like to highlight the importance of getting accurate grain size data, with particular reference to the determination of the hydrograph derived from a landslide dam failure. Many deterministic models attempt to approach this problem, by taking into account only the median percentile (D-50) of the cumulate grain size distribution. However, in most of the selected cases, a marked bimodal distribution was found in the frequency diagrams, so the fiftieth percentile (D;()) is often one of the less representative grain size classes. It should thus be taken carefully into account that this choice could be misleading, as it is not necessarily justified by the physical evidence. (C) 2002 Elsevier Science B.V. All rights reserved.