泥石流影响区建筑物暴露度及承灾力动态评价方法研究

Debris flow risk assessment is an important part of the natural hazards risk research in earthquake regions, which is essential for disaster prevention and reconstruction. Furthermore, the building vulnerability is the key point of debris flow quantitative risk assessment. During the period of rapid post-earthquake recovery and reconstruction, both the building exposure and resistance to debris flows are changing in time and space. However, there is no systematic research on their dynamic assessment methods. In this research, the debris flow catchments along the Min river main stream in Wenchuan county are selected as the study area. What's more, by means of field investigations, theoretical modeling and numerical simulations, this study tries to focus on the following aspects: (1) prediction method of debris flow threat ranges in earthquake areas; (2) dynamic assessment of building exposure in debris flow affected areas, which is based on the identification of exposure hotspots and establishment of fragile curve databases; (3) dynamic assessment of building resistance in debris flow affected areas, which is based on the vulnerability indicator system and impact of early-stage disaster damages and post-disaster recoveries. The objective of this study is to establish a dynamic assessment method system of building exposure and resistance, and to further reveal the dynamic change rules of building vulnerability under the influence of debris flows. Through this study, it will lay the foundation for dynamic assessment and scientific control of debris flow risk in earthquake zones.

泥石流风险评价是地震区自然灾害风险研究的重要内容，对震后防灾减灾与恢复重建具有重要价值，而建筑物易损性评价是实现泥石流风险量化的关键环节。在震后快速恢复重建期内，泥石流影响下的建筑物暴露度和承灾力均处于时空变化中，然而，关于其动态评价方法尚无系统研究。本课题选取汶川县岷江干流沿岸泥石流流域为研究区，力图通过现场调查、理论建模和数值模拟等手段，重点开展以下研究：（1）地震区泥石流威胁范围预测方法研究；（2）基于暴露热点区域识别和脆弱性曲线库构建，实现泥石流影响区建筑物暴露度的动态评价；（3）基于建筑物易损性指标体系，重点考虑前期灾害损伤和灾后恢复的影响，实现泥石流影响区建筑物承灾力的动态评价。本研究的目标是建立建筑物暴露度及承灾力动态评价方法体系，进一步揭示泥石流影响下建筑物易损性的动态变化规律，为实现地震区泥石流风险的动态评价和科学管控提供基础。

定量风险评价是泥石流灾害防灾减灾的重要措施，承灾体的易损性评价是其中的核心环节，传统的易损性评价方法，多将灾害体和承灾体之间关系静态化，但受灾害链效应和人类活动的影响，承灾体易损性的动态评价越来越受到重视。目前，对灾害体及其强度分布的动态分析已有一些进展，然而，承灾体自身属性引起的易损性时空变化仍未受关注。本项目从内部承灾力变化出发，基于易损性指标评价法，构建了泥石流威胁下的建筑物易损性动态评价模型。首先，在易损性评价指标的选择上，将其划分为内部承灾力和外部冲击力两个方面，并采用外部冲击力的影响因子作为灾害强度的间接表达；其次，基于FLOW-3D数值模拟和敏感性分析，探究了泥石流冲击力空间分布的影响因子，发现建筑物周围环境因素对泥石流冲击力影响显著，尤其是周围建筑物的方位角和距离，具体来说，周围建筑物的方位角可对泥石流强度产生遮蔽效应和渠化效应，结合建筑物距离因子，会产生遮蔽效应的放大和渠化效应的衰减作用；建筑物的朝向，主要通过接触面积、接近角和翻转冲击等，对泥石流冲击过程产生影响；建筑物的开口大小，则对泥石流峰值冲击力的影响较小。最后，我们利用汶川地震区143个受损建筑物样本，基于随机森林Boruta模型，筛选出影响建筑物损失的6个关键因子，分别为维护状态、开口质量、遮蔽效应、结构类型、开口位置和围墙；利用logistic回归构建了建筑物损失等级的预测模型；基于对泥石流区建筑物的长期监测，分别计算了不同阶段（灾前、灾后和恢复）的建筑物损失等级，发现灾后期的幸存建筑物易损性大幅增加，主要是前期灾害导致的建筑结构状态以及开口质量恶化所致，经过一段时间的灾后恢复，一些建筑物可恢复到灾前水平，除了建筑结构状态和开口质量外，围墙的防灾功能也得到了体现。另外，修建能产生遮蔽效应的建（构）筑物和调整开口位置，是需要加强的减灾方向。研究结果可为优化灾后恢复措施，减少泥石流灾害损失提供重要依据。