Fragmentation and boosting of rock falls and rock avalanches
Fragmentation and boosting of rock falls and rock avalanches
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DOI：
10.1002/2015gl064723
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发表时间：
2015-10-28
影响因子：
5.2
通讯作者：
Crosta, Giovanni Battista
中科院分区：
文献类型：
--
作者：
De Blasio, Fabio Vittorio;Crosta, Giovanni Battista
碎裂被认为是岩崩传播过程中一个重要的动力学过程。发生激烈的块碎片内的岩石雪崩光滑倾斜的地形上行驶的平坦区域（一个几何形状常见的许多滑坡）的数值研究首先通过一个离散元2-D代码，其中块受到相互碰撞和影响的地形。该数值模型证实，破碎化更可能发生的位置是那些在对应的坡度突变。因此，我们分析这种几何形状的影响在两种情况下：低和高的影响能量。在第一种情况下，根据最近的实验数据，运动学分析表明，撞击时释放的能量导致最小碎片的高速，这是岩石雪崩动力学中极有可能发生的情况。当影响是如此强大的瓦解滑坡，我们发现，在坡折处的爆炸性碎片提供了一个额外的水平推动岩石雪崩通过一个特殊的机制耦合的几何形状的斜坡路径的岩石雪崩的动态。结果，由于地形不对称性，导致沿水平方向沿着的净动量增益（增强）。然而，在正常的现场条件下，只有当倾角大于70度，破碎产生的碎屑大小相当均匀，动量和跳动距离显着增加。考虑到碎片大小和速度的范围，我们发现碎片程度和额外增强的幅度之间存在关系。
Fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches. The occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth inclined terrain followed by a flat region (a geometry common to many landslides) is first studied numerically by means of a discrete element 2-D code in which blocks are subjected to mutual collisions and impact with the terrain. This numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes. We thus analyze this geometry of impact in two cases: low- and high-impact energy. In the first case, where recent experimental data are available, a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments, a highly probable scenario in rock avalanche dynamics. When the impact is so energetic to disintegrate the landslide, we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche. As a consequence, a net momentum gain (boost) results along the horizontal direction due to the terrain asymmetry. However, under normal field conditions, only when the slope angle is greater than 70 degrees and fragmentation produces clasts of fairly uniform size, the momentum and runout distance are significantly enhanced. Allowing for a spectrum of fragment sizes and velocities, we find a relationship between the degree of fragmentation and the magnitude of the extra boost.