土石坝漫顶溃决的水沙、水土多过程耦合机制及数值模型研究

Earthen dam-break usually induces huge flooding which often cause serious disaster. Effective estimation and prediction of dam-break flooding process are great scientific significance end engineering value. Focusing on this kind of typical disaster of earthen dam overtopping failure, great attention would be paid on the mechanics mechanism in the process of dam-break development in this proposal. As the flow-sediment coupling and water-soil coupling coexisting in the dam-break process are regarded as the key in this problem, developing valid numerical methods which could deal with this multi-process coupling is crucial. By a series of laboratory scale dam-break experiments, we are going to analyze and carry out the full physics process of dam-break development, and to reveal the coupling mechanism of two processes of flow erosion on surface soil and soil body structure-break. The smoothed particle hydrodynamics (SPH) method, a Lagrange description based method, is employed in numerical simulation to describe the water flow, flow erosion and wall soil failure simultaneously and directly, especially the interactions between them explicitly. A new three dimensional dam-break numerical model based on the flow-sediment and water-soil multi-process coupling will be developed to realize the simulation on the full process of earthen dam-break. Thus, the characteristics of dam-break process in different conditions will be studied numerically in detail. Base on series of numerical experiments, the mechanism and law of main factors affecting dam-break will be analyzed, where novel knowledge could be obtained in this study. Finally, a demonstration of the numerical simulation study on practical dam-break problems will be carried out at last. And an effective and practical method for estimation and prediction of dam-break flooding disaster problems could be expected.

土石坝溃决常常引起巨大洪水并造成严重灾害，合理分析预测溃坝洪水过程具有重要科学意义和应用价值。本项目针对土石坝漫顶溃决这一典型灾害问题开展研究，重点关注溃坝口门发展过程中的复杂力学机制这一关键问题。以溃坝过程中同时存在水-沙耦合和水-土耦合作用为切入点，通过室内机理性溃坝实验，分析溃坝口门发展的完整物理过程，揭示水流对坝体冲刷和坝体自身土体结构破坏两个过程的耦合作用机理。采用基于Lagrange描述的光滑粒子动力学（SPH）方法，将水流运动、水流冲刷和边壁土体破坏统一起来，建立全新的基于水-沙、水-土多过程耦合的三维溃坝模型，实现对土石坝漫顶溃决物理过程的完整数值模拟。进一步通过数值模拟实验，分析不同条件下溃坝过程的基本特征，揭示主要因素的影响机制和规律，并开展初步的实际应用研究。为科学预测和评估土石坝漫顶溃决洪水灾害提供理论依据和分析方法。

我国目前依旧拥有大量土石坝，土石坝溃坝常常引起巨大洪水并造成灾害，合理分析预测溃坝洪水过程具有重要的科学意义和应用价值。本项目针对土石坝漫顶溃决这一典型灾害问题，系统研究了溃口演变的多过程耦合、堤坝溃决过程的动力学耦合数值模型、堤坝溃决的复杂水流运动和土体结构运动规律，取得如下重要进展。 (1) 针对土石坝溃决过程，深入分析了大量模型试验和部分实测资料，结合室内小尺度机理性实验，提出溃口发展过程中包含两个主要物理过程：一是洪水对坝体表面的冲刷过程，称之为水沙耦合过程；二是水流冲刷土体变形导致的坝体结构破坏，之为水土耦合过程。水沙耦合和水土耦合两个过程同时存在并不断交互作用，形成土石坝溃决的复杂水土耦合运动过程。（2）针对溃坝复杂流态和自由面大变形等特点，发展了自适应加密SPH方法，建立了三维复杂水流SPH数值模型。进一步，针对溃坝过程中水流与溃口变化快、相互作用强烈耦合的特点，采用N-S方程和土体弹塑性本构模型，应用无网格SPH方法，结合GPU加速技术，建立了漫顶溃坝过程的三维水土耦合数值模型。该模型能够较合理地描述土石坝漫顶溃决过程溃坝水流的复杂流动、对坝体的冲刷过程，以及坝体的坍塌过程。利用该数值模型，研究了典型堤坝溃决过程的水土耦合运动过程，给出了溃口发展运动和坍塌演变过程。（3）针对堤坝溃决过程中的水沙强耦合特征和溃口变化快，形状不规则的特点，建立了适用于工程快速评估的二维垂向积分形式水沙耦合溃坝和洪水演进模型。模拟计算了多个典型溃坝实验过程，模拟结果得到实验资料的良好验证，表明该模型能够比较好的模拟复杂地形的水流冲刷过程和床面地形的快速变化过程，在溃坝问题模拟中能够较精确地反映坝溃口快速发展中的水沙强耦合过程。应用发展的水沙土耦合SPH模型和二维垂向积分水沙耦合模型，开展了初步的工程应用研究，如梯级坝洪水增强机制、溢洪道滚波聚合机理、唐家山溃坝洪水与演进，为堤坝溃决洪水预报提供了有效的分析方法。