Abstract The deformation of rock slopes is associated with the formation and accumulation of internal and external features (such as tension cracks, rock mass bulging and dilation, rockfall, etc.) that can be comprehensively referred to as “slope damage”. In this paper, we use a 3D distinct element numerical modelling approach to investigate the role of shear zone morphology and groundwater pressure on the displacement and slope damage accumulation at the Downie Slide, a large, extremely slowly moving rockslide in British Columbia (Canada). First, we briefly review the external slope damage features that can be observed in an airborne laser scanner (ALS) dataset, allowing four slope damage domains (upper, central, northern, and southern domain) to be interpreted within the slide area, based on the orientation and type of features. Using the same ALS dataset we construct a 3D model of the present-day slope, explicitly including the two shear zones along which displacements occur, in order to investigate their role in the later stage of the landslide evolution. We assign a strain-softening constitutive model to the slide body, in order to account for the decrease in material properties due to damage accumulation. Virtual inclinometers are also implemented in the model, allowing for the comparison of simulated and observed displacement direction along the shear zones. The progressive deformation and failure of the slope is then simulated both assuming dry and wet conditions, in order to examine the role of pore water pressure, and the morphology of the upper and lower shear zones on the magnitude, orientation, and distribution of displacements. For each numerical model, the simulated slope damage features are recorded, by analyzing the zone volumetric strain and failure state, and compared with the type and orientation of features observed in each of the interpreted slope damage domains, thus allowing the numerical results to be better constrained and validated. It is clearly demonstrated that the orientation and distribution of slope damage and displacements observed in both the surface ALS and the subsurface borehole inclinometer data can be well reproduced in the 3D numerical models. Numerical modelling results show that the principal factor controlling the spatial distribution of slope damage at the Downie Slide is the morphology of the lower shear zone, whereas a negligible role is played by the upper shear zone morphology. We also observe that models incorporating a groundwater table display larger displacements, without significant effects on the orientation and distribution of simulated slope damage. This paper demonstrates that an analysis of slope damage is very important for understanding the mechanisms underlying the behavior of large landslides and should be a fundamental step in the comprehensive characterization of any major slope failure.

中文翻译：

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大型、缓慢移动的岩石滑坡中斜坡损坏的数值模拟：来自加拿大不列颠哥伦比亚省 Downie 滑坡的见解

摘要 岩质边坡变形与内外特征（如张拉裂缝、岩体胀胀、落石等）的形成和积累有关，可统称为“边坡损伤”。在本文中，我们使用 3D 不同元素数值建模方法来研究剪切带形态和地下水压力对 Downie Slide 的位移和斜坡损伤累积的作用，Downie Slide 是一个位于不列颠哥伦比亚省（加拿大）的大型、移动速度极慢的滑坡。首先，我们简要回顾了可以在机载激光扫描仪 (ALS) 数据集中观察到的外部斜坡损坏特征，允许在滑动区域内解释四个斜坡损坏域（上部、中部、北部和南部域），基于特征的方向和类型。使用相同的 ALS 数据集，我们构建了当今坡度的 3D 模型，明确包括发生位移的两个剪切带，以研究它们在滑坡演化后期的作用。我们为滑动体分配了应变软化本构模型，以解决由于损伤累积导致的材料特性下降。模型中还使用了虚拟测斜仪，可以比较模拟和观察到的沿剪切带的位移方向。然后在假设干燥和潮湿条件下模拟边坡的逐渐变形和破坏，以检查孔隙水压力的作用，以及上下剪切带的形态对位移的大小、方向和分布。对于每个数值模型，通过分析区域体积应变和破坏状态，记录模拟的斜坡损坏特征，并与在每个解释的斜坡损坏域中观察到的特征类型和方向进行比较，从而更好地约束和验证数值结果。清楚地表明，在地表 ALS 和地下钻孔测斜仪数据中观察到的斜坡损伤和位移的方向和分布可以在 3D 数值模型中很好地再现。数值模拟结果表明，控制 Downie Slide 斜坡损伤空间分布的主要因素是下剪切带的形态，而上剪切带形态的作用可以忽略不计。我们还观察到包含地下水位的模型显示更大的位移，对模拟斜坡损坏的方向和分布没有显着影响。本文表明，边坡损坏分析对于理解大型滑坡行为的潜在机制非常重要，并且应该是全面表征任何主要边坡失稳的基本步骤。