Collaborative Research: Multi-Dimensional and Multi-Physics Analysis of Rainfall-Induced Landslides and Runout

山体滑坡是一种持续的自然灾害，可以破坏基础设施，造成重大的生命损失，就像2014年3月22日发生在华盛顿州斯诺霍米什县的奥索山体滑坡一样。有些滑坡是快速的，在几分钟内就会出现大的跳动，而另一些则是间歇性的，在一年中只移动一小段距离。这两种危害通常都是由降水引发的。本研究项目的主要目标是开发一个包含非饱和土水力特性、有效应力和剪切强度的三维（3D）边坡稳定性框架，以更好地预测降雨引起的滑坡的位置、形状和深度，例如最近西雅图附近的Oso滑坡和洛杉矶附近的La Conchita滑坡（1995年和2005年）。所提出的3D模型将用于模拟水渗透引起的饱和度随时间的变化，地表植被和木材的影响，以及径流引起的静水孔隙水压力的上升，这些压力将用于根据计算的安全系数、坡角和触发后的孔隙水压力来预测跳动距离。本研究的关键成果将是一个新的有效的边坡稳定性分析和滑坡风险评估框架。这种三维变饱和稳定性分析框架很重要，因为它考虑了传统二维极限平衡边坡稳定性分析中没有纳入的以下因素：(1)饱和和非饱和条件下的有效应力；(2)应力相关的非饱和和饱和强度包膜；(3)三维滑块几何形状、体积、剪切力和边界条件；(4)滑块上非饱和带和静水孔水压力的空间变化和深度；(5)滑块上非饱和和饱和土抗剪强度的变化。目前二维分析的局限性影响了计算的极限平衡安全系数，从而影响了预测潜在滑动质量的发生、形状、体积和跳动距离的能力。例如，二维分析不能提供三维形状和体积的估计，而三维形状和体积是预测滑动质量体积、孔隙水压力和跳动距离的关键。该项目的成果将改进滑坡探测、预测、灾害测绘、土地利用规划和产权政策决策。对于新的分区，可以通过建议的3D分析识别岩土技术问题并调整分区，以管理风险。

Landslides are continual natural hazards that can damage infrastructure and cause significant loss of life as occurred in the Oso Landslide (March 22, 2014) in Snohomish County, Washington. Some landslides are rapid and exhibit large runout over few minutes, whereas others are intermittent and move only small distances in a given year. Both of these hazards are usually triggered by precipitation. The main objective of this research project is to develop a three-dimensional (3D) slope stability framework that incorporates unsaturated soil hydraulic properties, effective stresses, and shear strengths to better predict the location, shape, and depth of rainfall-induced landslides, such as the recent Oso Landslide near Seattle and the La Conchita Landslides (1995 and 2005) near Los Angeles. The proposed 3D model will be used to simulate time-dependent variations in saturation from water infiltration, impact of surface vegetation and timbering, and rises in hydrostatic pore-water pressures from runoff that will be used to predict the runout distance based on the calculated factor of safety, slope angle, and pore-water pressures after triggering. The key product of this research will be a new validated framework for slope stability analyses and landslide risk assessment. This 3D variably-saturated stability analysis framework is important because it accounts for the following factors that are not incorporated in traditional two-dimensional (2D) limit equilibrium slope stability analyses: (1) effective stresses under both saturated and unsaturated conditions, (2) stress-dependent unsaturated and saturated strength envelopes, (3) 3D slide mass geometry, volume, shear forces, and boundary conditions, (4) spatial variation and depth of the unsaturated zone and hydrostatic pore-water pressures across the slide mass, and (5) variation in unsaturated and saturated soil shear strength across the slide mass. Current limitations with 2D analyses affect the calculated limit equilibrium factor of safety and thus the ability to predict the occurrence, shape, volume, and runout distance of the potential slide mass. For example, a 2D analysis does not provide an estimate of the 3D shape and volume, which is key to predicting slide mass volume, pore-water pressures, and runout distance. The results of this project will improve landslide detection, prediction, hazard mapping, land-use planning, and property rights policy decisions. For new subdivisions the geotechnical concerns can be identified and zoning adjusted to manage the risk with the proposed 3D analysis.