Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation
Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation
复制标题
DOI：
10.5194/tc-11-217-2017
复制
发表时间：
2017-01-27
期刊：
影响因子：
5.2
通讯作者：
Schweizer, Juerg
中科院分区：
文献类型：
--
作者：
Gaume, Johan;van Herwijnen, Alec;Schweizer, Juerg
埋在粘性板层下面的弱雪层的破坏是发生干雪板雪崩的必要条件，但不是充分条件。弱层中裂缝的大小也必须超过一个临界长度才能穿过斜坡。与开创性的基于剪切的方法相比，最近的发展解释了弱层坍塌，并允许更好地解释从低角度地形远程触发的典型观测结果。然而，这些新模型预测的裂纹扩展临界长度几乎与坡角无关，这是一个相当令人惊讶和违反直觉的结果。在离散元模拟的基础上，提出了一种新的临界裂纹长度解析表达式。这个新模型调和了过去的方法，首次考虑了板弹性和弱层力学行为之间的复杂相互作用，包括其结构崩塌。当板坯加载和裂纹尖端变形引起的应力超过弱层破坏包络线的极限时，裂纹开始扩展。该模型能较好地模拟低角度地形下的裂纹扩展，并能较好地模拟随坡角增大而减小的临界长度。该模型与大量的野外数据吻合良好，且在积雪模型SNOWPACK中易于实现，为改进雪崩预报开辟了广阔的前景。
The failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new models predict a critical length for crack propagation that is almost independent of slope angle, a rather surprising and counterintuitive result. Based on discrete element simulations we propose a new analytical expression for the critical crack length. This new model reconciles past approaches by considering for the first time the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The crack begins to propagate when the stress induced by slab loading and deformation at the crack tip exceeds the limit given by the failure envelope of the weak layer. The model can reproduce crack propagation on low-angle terrain and the decrease in critical length with increasing slope angle as modeled in numerical experiments. The good agreement of our new model with extensive field data and the ease of implementation in the snow cover model SNOWPACK opens a promising prospect for improving avalanche forecasting.