强震条件下顺层滑坡堵江的动力灾变机理与演化全过程

China is a country with frequent earthquake-induced landslide river-blocking disasters. Especially in the southwest area of the China, these river-blocking landslides are of large quantity, strong destructive force and severe damage. Post-earthquake geologic investigations of these disasters indicate that most of the large-scale river-blocking landslides with the characteristics of “high speed, short routine and monolithic type” generally occur in the bedding rock slope. Based on the typical bedding landslide and the river-blocking barrier dam occurred during the Wenchuan earthquake, the geological engineering model can be obtained through the generalization of the actual slope. Utilizing the discontinuous deformation analysis (DDA) method to formulate the kinetic and computational mechanic model focused on large deformation, and redeveloping the DDA code by introducing the strength degradation contact model between adjacent blocks, dynamic damping of water pressure before the front edge of sliding body and frictional resistance of soil or sand at the bottom of sliding body, the whole dynamic evolution process of landslide river-blocking under actual seismic conditions can be reproduced and be validated by large-scale shaking table test relied on the PIV measurement technique throughout the whole depth of water. Then, in order to reveal the mechanism of dynamic catastrophe process and river-blocking pattern, simulating the complete process of river-blocking motion induced by sliding body systematically with various main affecting factors, such as valley topography, composition and structure of rock, hydrodynamics conditions (river width, water depth and river bed sediment thickness, etc ) , seismic loadings, and so on. In addition, conducting the comparative studies on various main control parameters to establish the relationships between main parameters and the velocity of sliding body, the final position, the volume of sliding body immerged into water, the height of barrier dam, etc. to put forward the general criterion of landslide river-blocking. The achievements of this research item can provide the scientific evidences for prediction of landslide river-blocking and disaster prevention and mitigation in earthquake regions.

我国西南地区地震频发，触发的岩质滑坡数量多、规模大、破坏力强，且往往造成滑坡堵江灾害。震害调查表明，大型堵江滑坡多见顺层岩质边坡，呈高速、短程、整体状运动特征。以汶川地震典型堵江顺层滑坡为依托，概化原型边坡工程地质模型，以DDA方法建立大变形运动学计算力学模型，引入强度衰减式块间接触模型、动态式滑体前锋压水阻尼和底部泥沙摩阻模式，对DDA数值程序进行二次开发，模拟强地震触发下滑坡堵江的动力演化过程，并基于水上-水下全程PIV量测技术的大型振动台试验进行验证；进而系统模拟不同斜坡地形与岩层组构、河水动力条件（水深和河床泥沙厚度）、地震荷载等主控因素下滑体堵江运动的完整演化过程，揭示其动力灾变机理和堵江模式；通过变动参数比较研究，建立各主控参数与滑体速度、前锋位置、入江体积、堰塞体高度等相应关系，提出地震滑坡堵江判据。该成果可为地震滑坡堵江预测、防灾减灾规划和地震应急处置对策制定提供科学依据。

我国西南山区地形复杂，沟壑峡谷纵横交错，河流地貌发育显著，且地震地质构造活跃，强震极易诱发山体滑坡堵塞峡谷或河道形成滑坡坝；且当堰塞湖内水位过高时，滑坡坝亦有可能因漫顶或管涌溃坝进而诱发洪水或泥石流等次生地质灾害链。本项目依托汶川地震典型滑坡堵江事件，构建工程地质力学模型，为数值模拟和模型试验提供依据。开展不同岩土体材料及其相似材料的静动力剪切试验，结合试验结果和理论分析，提出一种简单统一的状态依赖型剪切强度模型，用以描述滑坡过程中材料接触界面的强度衰减效应。结合非连续变形分析(DDA)数值方法和边坡抗滑稳定安全系数计算的矢量和方法(VSM)，发展岩质边坡地震稳定性的高效数值评价方法；基于状态依赖型的块间接触强度弱化模型，改进DDA数值方法，以真实滑坡体的堆积形态和堆积位置作为目标函数，复演地震触发滑坡启动、滑体运移、堆积稳定至堵江筑坝的动力灾变全过程，发现滑坡过程中坡体材料剪切强度参数的弱化效应能够显著影响其运移距离和堆积形态；特别地，研制一套集成摄影量测技术的滑坡堵江筑坝室内模型试验装置，检验前述DDA数值模拟方法。在此基础上，开发计算流体动力学和离散元方法(CFD-DEM)耦合的滑坡堵江模拟程序，进行U型和V型峡谷区域滑坡坝形成过程的模型试验和数值模拟，系统研究不同滑面倾角和河床倾角组合情况下滑坡坝的几何构型特点，构建U型和V型峡谷区域滑坡坝几何形态的快速预测模型；结果表明，滑面倾角对滑坡坝长度和高度具有显著影响，而河床倾角对其影响有限；此外，主要受滑面倾角影响的滑坡坝横截面形状可以归纳为对称型、非对称型和平直型。基于上述滑坡坝几何形态预测模型，结合逻辑回归原理，建立地震触发滑坡坝的坝长、坝宽及堰塞湖库容与滑坡堰塞坝稳定性之间的定量关系，用于指导滑坡坝稳定性的快速评估。上述成果可为地震滑坡堵江事件的预测、防灾减灾措施和应急处置对策的制定提供科学依据。