Do Precipitation-Induced Shallow Landslides Occur under Unsaturated Conditions?

非饱和条件下是否会发生降水引发的浅层滑坡？

• 批准号: 0855783
• 负责人: Ning Lu
• 金额: $ 17.4万
• 依托单位: Colorado School of Mines
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0855783&HistoricalAwards=false
• 关键词: Do; Precipitation; Induced; Shallow; Landslides

The socioeconomic impacts of natural landslides are enormous worldwide. In the U.S., natural landslides result in the loss of life, as well as property and environmental damages exceeding US$2 billion annually. Shallow landslides, typically translational slope failures a few meters thick of unlithified soil mantle or regolith, may dominate mass-movement processes in hillslope environments. They are particularly destructive when they initiate or coalesce to form debris flows. Shallow landslides and debris flows are commonly triggered by intense precipitation or strong ground shaking and may affect extensive areas during a single meteorological or seismic event. According to a recent survey, about half of the 40 most destructive landslide disasters worldwide in the past century resulted from prolonged or intense rainfall. Recent advances in the scientific understanding of landslide initiation, particularly for those landslides that occur under intense or prolonged precipitation in hillslope environments around the world, indicate that the failure surface may be above the water table and under nearly saturated conditions. The classic methodology for landslide analysis assumes that earthen materials are either fully saturated or completely dry neglecting the contribution of soil suction to the stability of slopes. Thus this methodology is overly conservative and incapable of accurately forecasting shallow landsliding. Recent advances in soil mechanics have shed light on the state of stress in partially saturated soil masses. Furthermore, physical evidence and scientific understanding in both geomechanics and geomorphology all point to the likelihood that the failure surface of infiltration-induced landslides may occur above the water table and under nearly saturated conditions.This project seeks further physical evidence and uses the new knowledge in defining stress in partially saturated soil to identify the likelihood of landslide initiation under partially saturated soil conditions. The overall goals of this research are: to test the hypotheses that (1) landslides, particularly shallow and translational slope failures under heavy precipitation conditions, can occur above the water table; and, (2) that the failure occurs when materials are nearly saturated and suction stress is reduced to nearly zero. To test these hypotheses, we will: (1) measure the unsaturated hydrologic and mechanical properties under laboratory settings, (2) conduct landslide initiation tests using an intermediate-scale shallow landslide simulator, and (3) implement a site-specific program for long-term, real-time monitoring for shallow landslide occurrence, thus examining the validity of both hypotheses at the field scale. By clarifying whether shallow landslides occur under saturated or unsaturated conditions, this work provides a physical basis for answering the important question regarding whether we need a new paradigm that includes either soil suction or effective stress or both to predict shallow landslides. Knowledge gained here is transformative to advancing the understanding of the interactions among climate change, topography, and sustainable land use. Mass movement due to shallow landslide initiation under heavy precipitation is part of long-term landform evolution, and presents a great challenge for society subject to climate change and evolving land use. Testing the concept of effective stress variation above the water table for landslide initiation analysis provides a sound physical basis for future predictive models and will enhance our ability to predict and forecast shallow landslide hazard. Collaboration with the USGS National Landslide Information Center ensures broad dissemination via outreach activities targeted toward researcher, K-12 students, and the general public. Integrating the research mission with an educational and diversity mission via graduate and undergraduate student training, proactive recruitment of underrepresented groups and incorporating the research activities into existing courses ensure broad impact to a diverse audience of students, researchers, and practitioners.

自然滑坡的社会经济影响在世界范围内是巨大的。 在美国，天然滑坡每年造成的生命损失、财产和环境损失超过20亿美元。 浅层滑坡，通常是几米厚的未石化的土壤覆盖层或风化层的平移边坡破坏，可能主导山坡环境中的质量运动过程。当它们开始或合并形成泥石流时，破坏性特别大。 浅层滑坡和泥石流通常是由强降水或强烈的地面震动引发的，在一次气象或地震事件中可能影响到广泛的地区。 根据最近的一项调查，在过去世纪全世界40起最具破坏性的滑坡灾害中，约有一半是由长时间或强降雨造成的。 对滑坡形成的科学认识的最新进展，特别是对世界各地山坡环境中强降水或长时间降水下发生的滑坡的科学认识，表明破坏面可能在地下水位以上，处于接近饱和的条件下。 滑坡分析的经典方法假定土材料要么完全饱和，要么完全干燥，忽略了土壤吸力对边坡稳定性的贡献。 因此，这种方法过于保守，不能准确预测浅层滑坡。 土力学的最新进展揭示了部分饱和土体的应力状态。此外，物理证据和地质力学和地貌学的科学认识都表明，渗透诱发滑坡的破坏面可能发生在地下水位以上和接近饱和的条件下。本项目寻求进一步的物理证据，并使用定义部分饱和土壤应力的新知识来确定部分饱和土壤条件下滑坡发生的可能性。本研究的总体目标是：验证以下假设：（1）滑坡，特别是在强降水条件下的浅层和平移边坡破坏，可能发生在地下水位以上;（2）当材料接近饱和且吸力应力降低到接近零时，会发生破坏。为了验证这些假设，我们将：（1）在实验室环境下测量非饱和水文和力学特性，（2）使用中等规模的浅层滑坡模拟器进行滑坡启动测试，以及（3）实施特定于现场的计划，对浅层滑坡的发生进行长期实时监测，从而在现场规模上检验两种假设的有效性。 通过澄清浅层滑坡是否发生在饱和或非饱和条件下，这项工作提供了一个物理基础，回答的重要问题，我们是否需要一个新的范例，包括土壤吸力或有效应力或两者兼而有之，以预测浅层滑坡。 在这里获得的知识是变革性的，以促进对气候变化，地形和可持续土地利用之间的相互作用的理解。 强降水条件下浅层滑坡引发的块体运动是长期地貌演变的一部分，对气候变化和土地利用演变的社会提出了巨大挑战。 测试的概念有效应力变化的地下水位以上的滑坡启动分析提供了一个良好的物理基础，为未来的预测模型，并将提高我们的能力，预测和预报浅层滑坡灾害。 与美国地质勘探局国家滑坡信息中心合作，确保通过针对研究人员，K-12学生和公众的外联活动进行广泛传播。 通过研究生和本科生培训，积极招募代表性不足的群体并将研究活动纳入现有课程，将研究使命与教育和多样性使命相结合，确保对学生，研究人员和从业人员的不同受众产生广泛影响。