青藏高原东缘古滑坡复活机理与早期识别研究

The old landslide has special material structure and the feature of imperceptibility. The risk of old landslide reactivation is substantially increasing due to the increase of intensified human engineering activities and the frequency of extreme weather events. Many old landslides have been reactivated all over the world and led to serious fatalities and severe damage to many important engineering facilities such as transportation and hydropower engineering projects. However, due to the exceptional material composition and mechanical properties, it is difficult to explain the evolution process of old landslide using traditional strength and failure theory. And therefore, the research on the theory and methodology of reactivation mechanism of old landslide and its early recognition has become an international scientific hot issue. The project aims to reveal the reactivation mechanism and establish the methodology of its early recognition. We will explore the regional distribution pattern of old landslides and their geological forming types by means of sufficient field geological survey and case studies of large number of old landslides in the Bailong River-Min River-Dadu River-Jinsha River area, eastern margin of Tibetan Plateau, and then establish the identification criteria of the old landslides. The strength theory of old sliding belt will be proposed once we understand the engineering geological characteristics of the old landslide materials and the interface effect of the sliding belt by the methods of in-situ tests, laboratory tests, large-scale physical experiments and numerical simulation. The reactivation mechanism and process of old landslides will be revealed under different triggering conditions including heavy rainfall, slope toe excavation, and reservoir water storage. The predictive model will be built by coupling multi-fields information. This study will propose the early recognition method and theory for old landslide reactivation under complex conditions based on the multiple-index monitoring information. The scientific theory and methodology achieved by this project will facilitate the planning and site selection of major projects as well as the disaster prevention and reduction in old landslide developing areas.

古滑坡具有极强的隐蔽性和物质结构的特殊性。随着人类工程活动不断加剧和极端天气频繁出现，国内外发生大量古滑坡复活导致的交通、水电工程等重要设施毁坏和人员伤亡等灾难性事件，灾害风险日益严峻。然而，由于古滑坡特殊的物质组成和岩土力学性质，传统的强度和破坏理论难以解释其演化过程，古滑坡的复活机理与早期识别研究成为国际性科学难题。本项目拟通过青藏高原东缘白龙江-岷江-大渡河-金沙江一带大量原型案例研究，分析总结古滑坡发育的区域规律和地质成因模式，提出古滑坡的判识准则。采用现场测试、室内试验、大型物理模拟、数值分析等技术方法，揭示古滑坡堆积体和古滑带的工程地质特性，建立古滑带强度演变理论；通过剖析强降雨、坡脚开挖、水库蓄水等作用下古滑坡的复活机理和过程，建立多场耦合的古滑坡复活预测模型。基于多元监测信息，提出复杂条件下古滑坡复活的早期识别方法和判据，为重大工程规划选址和防灾减灾提供新的理论和技术支撑。

针对青藏高原东缘重大工程和城镇建设面临的大型古滑坡复活机理与风险防控方面的关键科学问题，以白龙江-岷江-大渡河-金沙江一带为重点研究区，采用高分辨率遥感解译、地面调查、InSAR监测、岩土力学试验、物理模型试验和数值模拟分析等方法，开展了古滑坡区域发育规律与判识、古滑坡滑带土的强度演变、古滑坡复活机理与演化过程、古滑坡复活早期识别与监测方法等方面的研究，取得如下重要成果：. （1）在古滑坡发育规律与有效判识方面，总结了大渡河和岷江上游古滑坡的主要发育特征、形成时代和区域发育规律，提出了古滑坡主要形成于河流强烈下切阶段，时间跨度为10～40ka BP，总体上受气候变化影响显著，构造活动造成了古滑坡空间分布的差异性。基于多源高分辨率遥感数据，采用植被指数、地形粗糙度和灰度矩阵熵等指标，建立了古滑坡综合遥感判识模型。. （2）在含砾滑带土强度演变机制方面，进一步明晰了启动强度、残余强度、恢复强度之间的关系；采用能谱密度和相对起伏度均方根定量表征了含砾滑带土剪切面粗糙度，建立了滑带土宏观力学与细观结构的联系；揭示了含砾滑带土抗剪强度由细粒土基本强度和剪切面起伏角共同影响的机制，提出了考虑砾石效应的滑带土强度修正公式。. （3）在古滑坡复活机理方面，剖析了降雨、河流侵蚀、人类活动及内外动力耦合作用诱发古滑坡复活的成因机理，建立了古滑坡复活的典型模式；发现了地表水沿优势通道快速入渗是古滑坡复活的重要条件，采用物理模拟和数值模拟再现了不同裂缝组合工况下的滑坡渗流与失稳规律，初步形成了介质与驱动力耦合作用对古滑坡复活的联合控制理论，突破了前人对降雨促发滑坡机制的认识。. （4）在古滑坡复活的早期识别方面，提出了古滑坡不同复活演进阶段的判据，将初始变形与匀速变形之间的拐点作为古滑坡复活的起点标志，把匀速变形向加速变形转变的拐点作为复活失稳的标志。创新提出了基于InSAR技术的古滑坡复活早期识别方法，建立了多个集InSAR早期识别-地表GNSS位移监测-深部多参数监测于一体的古滑坡野外监测站。. 研究成果显著提升了对青藏高原东缘古滑坡复活机理的认识，为古滑坡复活灾害监测预警和风险防控提供了重要应用基础理论和技术方法，在重大工程规划选址和防灾减灾中发挥了重要作用。