Abstract. The Köfels Rock Slide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the i) pre-failure and failure topography, ii) failure volume and porosity of the sliding mass, and iii) shear strength properties of the gneissic rock mass obtained by back-calculations. Geographic information system methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3.1 km³ and 4.0 km³, respectively and a sliding mass porosity of 26 %. For the back-calculations the 2D discrete element method was applied to determine the shear strength properties of the reconstructed basal shear zone. Results indicated that under no groundwater flow conditions, a very low friction angle below 24° is required to promote failure, whilst, with groundwater flow, the critical value increase to 28°. Such a low friction angle is unexpected from a rock mechanical perspective for this strong rock and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rock slide. Additional conditioning and triggering factors should be identified by further studies, for example focussing on the impact of dynamic loading.

中文翻译：

---

基于GIS的Köfels岩石滑坡的地形重建和地质力学建模

摘要。Ötztal山谷（奥地利蒂罗尔）的Köfels岩石滑坡是阿尔卑斯山变质岩体中已知最大的极快速滑坡。尽管过去曾讨论过许多关于触发的假设，但到目前为止，尚未发现科学证明的触发因素。这项研究提供了有关以下方面的新数据：i）故障前和破坏的形貌，ii）滑动体的破坏体积和孔隙率，以及iii）通过反算获得的片麻岩岩体的抗剪强度特性。在事件发生之前，之中和之后，都使用了地理信息系统方法来重建斜坡地形。比较所得的数字地形模型可以得出3.1 km ³和4.0 km ³的破坏和沉积质量的体积估计，滑动质量孔隙率分别为26％。对于反算，应用了二维离散元方法来确定重建的基础剪切带的抗剪强度特性。结果表明，在没有地下水流的情况下，需要一个低于24°的非常低的摩擦角来促进破坏，而在地下水流的情况下，临界值增加到28°。从岩石力学的角度来看，如此低的摩擦角对于这种强大的岩石和地下水流是不可预料的，即使假设水压很高，也可能无法触发该岩石滑动。其他条件和触发因素应通过进一步研究确定，例如，关注动态载荷的影响。