【作者】 吴火珍；

【导师】 焦玉勇；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2010， 博士

【摘要】 我国是一个地震多发的多山国家,由地震引起的山体滑坡频繁发生,并且极具破坏力,对山区人民的生命和财产安全造成了巨大的威胁。本文主要研究地震滑坡的共振效应,基于模态分析原理,提出了一种新的地震滑坡安全性评价方法—地震滑坡频谱分析方法(Analysis of Seismic Landslide Spectrum,简称ASLS)。主要研究内容如下：(1)基于经典三维Delaunay算法,研究了一种三维约束Delaunay三角化网格划分算法。该算法中,对实体边界的描述采用点、线和面组成的联合体；通过边界的恢复保证了边界的一致性和完整性,实现约束Delaunay四面体网格的自动生成；由于所有的四面体网格生成算法都可能出现质量不佳的单元,针对这类问题,本文提出了一种网格质量参数及其计算方法,即通过四面体外接球半径与其最短边长度的比值和四面体体积与其外接球体积的比值来控制单元质量,对质量不佳的单元加入结点进行优化,另外,对几何形状复杂的实体,特别是含有薄层的地质体,通过在实体上增加约束提高单元的质量并缩短计算时间。根据上述算法,编制了三维有限元网格自动剖分程序。(2)地震对滑坡形成的影响,主要是通过坡体波动振荡来产生。波动振荡在滑坡体变形、破坏过程中主要产生两种效应：累进破坏效应和触发效应,这两种破坏效应在地震荷载主频与边坡岩土体固有频率接近时会被放大很多倍,因此,地震波在岩土体中传播,特别是接近地表时,岩土体的频谱特征是影响地震对岩土体破坏作用的直接因素。地震发生时,滑体往往有选择性地放大特定频域的地震波,从而引起剧烈振荡导致灾害的发生,这是一种典型的共振现象。(3)将模态分析法引入地震滑坡的安全性评价中,根据动力有限元基本方程,建立了三维地震滑坡频谱分析的理论框架,提出了滑坡体固有频率和振型的计算方法,结合有限元前处理程序模块,编制了地震滑坡频谱分析方法VC++程序ASLS。提出了地震滑坡动安全系数的概念和计算方法,参考《中国地震动参数区划图》中的地震动反应谱特征周期,得到其特征频率,求出该频率与计算得到的滑坡体固有频率的比值,该比值即定义为动安全系数,仿照《建筑边坡工程技术规范》和《公路工程抗震设计规范》安全系数的确定方法,根据动安全系数与1的接近程度来评价滑坡体在我国工程抗震设防标准内的地震作用下的动安全性。对安全性不足的滑坡体,采取相应的加固措施,改变其固有频率,预防地震滑坡的发生。(4)设计并开展了地震滑坡振动台模型试验。采用素混凝土作为制作滑坡模型的材料,在地震模拟振动台上进行振动试验。对每一个滑坡体进行多次振动试验,每次输入频率不同振幅相同的地震波,根据输入波的频率和记录的滑坡体的位移,找出滑坡体位移最大时的频率范围,即可认为滑坡体的固有频率在该频率范围内,并将试验结果与ASLS计算结果进行对比分析。(5)采用自行编写的程序,对两端固定的等截面悬臂梁固有频率和振型计算、均质边坡的安全性评价和三峡库区内某滑坡体的安全性评价作了相关的计算。更多还原

【Abstract】 In our country, earthquakes frequently occur, meanwhile, a large number of mountains exist, so mountain landslides induced by earthquake often occur. The destructive power of landslide is great, and generally poses a great threat to the safety of life and property of people in mountain area. In this paper, we mainly study the resonance effect of the seismic landslide. Then based on the modal analysis theory, a new method to evaluate the safety of seismic landslide (Analysis of Seismic Landslide Spectrum, ASLS for short) is proposed. The main research contents are as follows:Base on the classical 3D Delaunay algorithm, an algorithm for 3D constrained Delaunay triangulation mesh generation is studied. The boundary of entity is described by the combo consisted of point, line and surface. And by restoring the constrained boundary and removing the local degeneracies, the consistency of solid boundary and the uniqueness of mesh can be guaranteed. In this way, the constrained Delaunay tetrahedral mesh can be effectively generated for any complex 3D solids with constraints. By using any tetrahedral mesh generation method, some low-quality elements may be generated, and according to this problem, the paper presents quality parameters and its calculation method, that is by controlling the magnitude of the ratio of circumradius length to the shortest edge length and the ratio of the tetrahedron volume to its circumscribing sphere volume to control the element quality. For the low-quality tetrahedral element, the mesh is optimized by adding new point. In addition, for the entity with complicated geometry, especially the geologic body containing thin layers, adding constraints can improve the mesh quality and shorten the calculation time. Finally, based on the above algorithm, the program for 3D finite element mesh automatic generation is developed.The effect of earthquake on the formation of landslide is mainly by the wave oscillation of landslide body. The wave oscillation produces two effects in the process of the deformation and failure of the landslide. They are the progressive failure effect and trigger effect. The two failure effects are magnified many times when the main frequency of earthquake load is close to the intrinsic frequency of rock-soil mass. So, when the seismic wave propagates in the rock-soil mass, especially close the surface, the spectrum characteristic of rock-soil mass is the direct factor of affecting the earthquake destructive effect on the rock-soil mass. During earthquake, the landslide often selectively magnifies the seismic wave in some frequency domain, and the intensive oscillation has arisen and induces the occurrence of disaster. It is a typical resonance phenomenon.The modal analysis theory is introduced into the evaluation of seismic landslide. Based on the basic dynamic finite element equations, the 3D theory framework of seismic landslide spectrum analysis is established, and the calculation method of the landslide intrinsic frequency and vibration mode is proposed. Combining with the pre-processing program module of finite element method, the program ASLS is developed. The concept and its calculation method of the dynamic safety factor for seismic landslide are proposed. With reference to the seismic response spectrum characteristic period of seismic parameter zoning map of China, the characteristic frequency of the area can be obtained. The ratio value of the characteristic frequency to the calculated intrinsic frequency of landslide is obtained, ant it is defined as dynamic safety factor. With reference to the method to define the safety factor under seismic load in Specifications of Earthquake Resistant Design for Highway Engineering and Technical Code for Building Slope Engineering, the dynamic safety of landslide under the earthquake in the engineering seismic fortification criterion of China is evaluated by the approaching degree between the dynamic safety factor and ’1’. For the unsafe landslide, its failure can be prevented by taking some reinforcement measures to change its intrinsic frequency.The shaking table model test of seismic landslide is designed and carried out. The plain concrete is used to make the landslide models. For each landslide, several vibration tests under different frequency seismic waves are performed. According to the dynamic responses of the landslide model, the frequency range corresponding to the largest displacement of landslide can be found, and it is considered that the intrinsic frequency of landslide is within the frequency range. Finally, the test results and the calculated results of ASLS are comparatively analyzed.By using the self-developed program, the intrinsic and vibration mode of a constant-section cantilever beam fixed by two ends are calculated, the safety of a homogeneous slope is evaluated, and the safety evaluation of a certain landslide in the reservoir area of Three Gorges Project is performed.更多还原