泥石流冲击桥墩动力作用物理模型构建与数值模拟

The frequent impact of debris flow is a major threaten to the bridge piers located in debris flow gully of the western mountain areas of China. To minimize this threaten, there is an urgent need to quantitatively model the dynamic impacting action and find out its numerical solutions efficiently. The difficulties arise from the fact that debris flow is a solid-liquid two-phase flow, and the impact action accompanies with complex elastic plastic deformation and quick energy transformations. Based on the failure cases in the Wenchuan seismic fields, we attempt to conduct the cause-analysis of the bridge pier destruction under the impact load of debris flow and construct the geomechanical model of the impact action. Then based on theoretical analysis and model experiment and through mathematical abstractions, a coupling solid-liquid physical model of the impacting action of debris flows to bridge piers is to be built. Finally, the ALE (Arbitrary Lagrange-Euler) efficient algorithm is to be adopted and improved in order to build up the numerical simulation platform for this model. The aim of this proposed study is to provide theoretical and technical supporting for quantitative risk assessment and structural optimization of the prevention engineering in the impacting event of debris flows to bridge piers.

伴随泥石流频发，尤其在我国西部山区的地震地质活跃带，泥石流灾害对位于泥石流沟道、沟口等位置处的桥墩构成重大威胁。泥石流是固液两相流，对桥墩冲击伴随复杂的弹塑性变形、短历时的能量转化，如何定量描述泥石流冲击桥墩动力过程，探索高效数值模拟方法，是泥石流冲击桥墩减灾领域拟要解决的一个重要科学问题。为此，在对汶川震区泥石流冲击桥墩失效案例的详细调查基础上，开展泥石流冲击荷载下桥墩破坏的成因机制分析，建立泥石流冲击桥墩的地质力学模型；基于理论分析、模型实验，经数学抽象，构建泥石流冲击桥墩动力作用流固耦合物理模型；引入并发展ALE（任意拉格朗日—欧拉）高效算法，搭建泥石流与桥墩冲击动力作用数值模拟平台，最终为泥石流冲击桥墩易损性评价、定量风险评估及工程防治结构设计提供理论及技术支持。

泥石流对位于河道、泥石流沟口等位置处的桥墩构成重大威胁，尤其以泥石流-桥墩动力冲击作用最为明显。泥石流是固-液两相流，固液相之间存在复杂的相互作用，同时，其强大冲击作用会导致桥墩产生变形破坏，桥墩的存在又对泥石流的流动造成显著影响，如何定量描述泥石流-桥墩冲击过程，揭示泥石流与桥墩冲击动力作用机理，是亟待解决的一个重要科学问题。项目以泥石流灾害威胁交通运输沿线桥墩的工程背景为基础，依托于地质灾害防治与地质环境保护国家重点实验室崩滑流试验室的室内多功能大型泥石流模拟系统，进行多组室内大比例泥石流冲击桥墩物理模型试验。研究泥石流容重、速度、流体高度以及粘性与泥石流冲击力的相关性，获得泥石流对桥墩冲击力以及桥墩的动力响应机制，建立泥石流冲击指标和桥墩动力响应的模型，采用基于深度积分的连续介质力学的方法来对多组大尺度的泥石流冲击桥墩的室内物理模型试验进行数值模拟，并开展了泥石流桥墩绕流动力学模拟研究，从而为桥墩抗泥石流冲击设计提供技术支持及科学依据。