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

山体滑坡是持续不断的自然灾害，可能会破坏基础设施并造成重大生命损失，华盛顿州斯诺霍米什县的奥索山体滑坡(2014年3月22日)就是这样发生的。有些滑坡速度很快，在几分钟内就会出现大的滑坡，而另一些滑坡则是间歇性的，在给定的一年里只移动了很小的距离。这两种危害通常都是由降水引发的。该研究项目的主要目标是开发一个结合非饱和土壤水力特性、有效应力和剪切强度的三维(3D)斜坡稳定框架，以更好地预测降雨引发的滑坡的位置、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)。所提出的三维模型将被用来模拟由于水分渗透、地表植被和支架的影响而引起的饱和度随时间的变化，以及来自径流的静水孔压的上升，这些孔压将被用来根据计算的安全系数、坡角和触发后的孔压来预测超限距离。这项研究的主要成果将是一个新的验证框架，用于斜坡稳定性分析和滑坡风险评估。这种三维变饱和稳定分析框架很重要，因为它考虑了传统的二维极限平衡边坡稳定分析中没有考虑的下列因素：(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络，(3)三维滑体几何形状、体积、剪力和边界条件，(4)非饱和带和滑体上的静水孔压的空间变化和深度，以及(5)滑体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块的发生、形状、体积和跳动距离的能力。例如，二维分析不提供对三维形状和体积的估计，而三维形状和体积是预测滑坡体体积、孔隙水压力和跳动距离的关键。该项目的成果将改进滑坡检测、预测、危险地图绘制、土地利用规划和产权政策决策。对于新的分区，可以确定岩土工程问题并调整分区，以利用拟议的3D分析来管理风险。

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.