建筑学论文涉水边坡稳定性的三维强度折减有限元分析.doc

涉水边坡稳定性的三维强度折减有限元分析 涉水边坡稳定性的三维强度折减有限元分析 three-dimensional slope stability analysis by shear strength reduction finite element method (ssr-fem) under drawdown condition【中文摘要】 强度折减有限元法能够考虑土体的应力应变关系,能够自动搜索滑动面的位置及模拟边坡的渐进性破坏过程而受到广泛关注。但该方法尚存在一些问题需要进一步探讨,如有限元网格对计算精度的影响,失稳判据统一性问题,如何将该方法合理应用于考虑库、河、海水位升降等荷载作用下边坡稳定性评价,将该方法从二维拓展到三维的合理性等问题都是值得进一步验证和研究的。针对上述问题,本文主要开展了以下三个方面的研究工作:1.讨论了单元形状、单元类型、网格大小等因素对边坡稳定系数计算精度和变形破坏效果的影响;分析了有限元网格与单元类型对边坡失稳判据的适宜性,对采用合理网格下边坡失稳四种判据的一致性和统一性进行了讨论;探索了边坡土体的黏聚力、内摩擦角及坡角等因素对滑动面和滑出点位置的影响;讨论了不同坡度、坡高、黏聚力和内摩擦角条件下均质边坡的稳定安全系数,并将强度折减有限元解与极限分析上限解进行了对比分析;最后将强度折减有限元法应用于各种复杂条件下的边坡稳定性分析中。2.分析了三种水位下降模式下边坡的失稳机理与稳定安全系数。水位下降模式可分为骤降、缓降及非饱和非稳定渗流三种类型。采用强度折减有限元方法分析水位在骤降和缓降条件下,岸坡的整体稳定性及其失稳机理。进一步地,通过对大型有限元软件abaqus的二次开发,采用visual fortran 6.5对边坡迎水面的边界条件进行改进,使水位可随时间变化合理模拟非饱和非稳定渗流。着重从水位下降模式、浸润线位置、土体的渗透系数、水位下降速率和下降比等五个方面深入而系统地探讨渗流条件下边坡的稳定性及其影响程度。此外,研究了非饱和区基质吸力对边坡稳定安全系数的影响。在以上工作基础上,进一步讨论了多因素影响下强度折减有限元边坡稳定安全系数的图表表达形式,包括土的黏聚力与内摩擦角、边坡坡角、土的渗透系数、水位下降速率、水位下降比等对安全系数的影响,建立了便于工程上广泛采用的简化图表法。最后讨论了土体的剪胀性对边坡安全系数和滑动面位置的影响。3.将强度折减有限元法拓展到三维边坡稳定性分析。通过典型算例校核强度折减有限元法三维边坡稳定分析中的可行性。研究土体的材料参数、长高比、几何形状、边界条件等因素对三维边坡稳定性和滑动面位置的影响,并与二维边坡的计算结果进行对比分析。在此基础上,将三维边坡强度折减有限元法应用于抗滑桩加固边坡的变形与稳定性分析中,并近一步将强度折减有限元法应用于三维涉水边坡的稳定性分析。【英文摘要】 more and more attentions have been paid to shear strength reduction finite element method(ssr-fem) for slope stability analysis.because it has the advantages as follows:(1) no assumption to be made in advance about the shape of the failure surface;(2) considered non-linear stress-strain relation on soil;(3) simulation of progressive failure of slopes.but some problems need to be studied in advance.for example,mesh shape,size and order for the accuracy of the calculation;failure criteria;how to analyze slopes stability by shear strength reduction finite element method(ssr-fem) under transient unsaturated seepages and whether it is rational that ssr-fem is extended to 3d slope.they are worthy of further study.the main research work done in this thesis consists of the following parts.1.the effect of mesh shape,size and order on the factor of safety is systematically discussed at first.the effect of mesh on the failure criteria is then studied.when a slope arrives at the critical failure state by ssr-fem used rational mesh shape,size and order,the four failure criteria as plastic zone extension from the toe to the top of slope,equivalent plastic strain exceeding a certain value developed along the potential slip surface,uncontrollable increase in characteristic nodal displacement on slope surface and the iteration non-convergence of nonlinear fem numerical calculations can be found in turn.discussed calculation results which showed the four evaluation criteria are highly consistent.location of potential slip surface and out-slip point is associated with cohesion,internal friction angle and slope angle. the factors of safety obtained by the limit analysis method and ssr-fem are compared for various slopes with different slope angle,slope height,cohesion and internal friction angle. moreover,ssr-fem is also applied to the stability of slopes under complex conditions.2.the safety factor of slope stability and failure mechanism are systematically discussed under various drawdown condtions.water drawdown conditions can be divided into three modes as rapid drawdown,slow drawdown,simple transient unsaturated seepage or transient unsaturated seepage.shear strength reduction finite element method(ssr-fem) has been applied to analyze the slope stability and failure mechanism under water rapid and slow drawdown,the factors of safety achived are compared with those by the limit analysis method(lam).the transient unsaturated seepage in soil slope is systematically investigated and the stability of a slope is analyzed by ssr-fem.emphases are given to discuss the influence of cohesion,internal friction angle,slope angle,location of phreatic surface,soil permeability,drawdown ratio,drawdown rate and matfic suction subjected to transient unsaturated seepage on the slope stability.and the effect of dilatancy on factors of safety and location of potential slip surfaces is also discussed.3.shear strength reduction finite element method(ssr-fem) has been applied to the stability of three-dimensional slopes.for further verification of the present method,a series of 3d analysis has been presented for comparison with results obtained by various investigators using other 3d slope stability techniques.their results are in good agreement.the factors of safety and location of slip surfaces are associated with slope length/width,boundary conditions, material parameters,geometry dimension,retaining structure.furthermore,it is compared with the factors of safety of 2d slopes.the 3d ssr-fem is finally used to analyze the stability of slope under water drawdown con&ion.【中文关键词】 边坡稳定; 强度折减有限元法; 失稳判据; 滑动面位置; 水位下降模式; 非饱和-非稳定渗流; 浸润线; 三维边坡 【英文关键词】 slope stability; strength reduction finite element method(ssr-fem); instability criteria; critical slip surfaces location; water drawdown conditions; transient unsaturated seepage; phreatic surface; three-dimensional slope 【毕业论文目录】摘要 4-5 abstract 5-6 1 绪论 11-23 1.1 引言 11-12 1.2 边坡稳定性分析方法 12-16 1.2.1 边(滑)坡稳定安全系数的定义 12-14 1.2.2 边坡稳定分析中的极限平衡法 14-16 1.2.3 强度折减技术在边坡稳定分析中的发展和应用 16 1.3 考虑渗流作用的边坡稳定性研究现状及存在的问题 16-18 1.3.1 极限平衡法在涉水边坡稳定性分析中的应用 17 1.3.2 强度折减有限元法在涉水边坡稳定性分析中的应用 17-18 1.4 三维边坡稳定性分析研究现状及存在的问题 18-20 1.5 本文的主要研究内容及技术路线 20-23 1.5.1 本文的主要研究内容 20-21 1.5.2 采用的技术路线 21-23 2 边坡稳定性分析的强度折减弹塑性有限元数值分析方法 23-55 2.1 引言 23 2.2 计算方法与数值实施 23-30 2.2.1 有限元分析软件abaqus 23-24 2.2.2 计算模型 24-30 2.2.3 强度折减技术 30 2.3 有限元网格对计算边坡稳定安全系数的影响 30-41 2.3.1 网格疏密及单元阶次的影响 30-39 2.3.2 相对网格大小 39-41 2.4 单元类型与尺寸对失稳判据的适宜性 41-44 2.4.1 四边形一阶单元 41 2.4.2 四边形二阶单元 41-42 2.4.3 三角形二阶单元 42-43 2.4.4 四种失稳判据的联系与对比 43-44 2.5 边坡破坏模式及影响因素分析 44-47 2.5.1 内摩擦角对临界滑动面位置的影响 44-45 2.5.2 黏聚力对临界滑动面位置的影响 45-46 2.5.3 坡角对临界滑动面位置的影响 46-47 2.6 计算精度对比 47-48 2.7 复杂边坡稳定性分析 48-54 2.7.1 成层土坡稳定性分析 48-50 2.7.2 复杂土层边坡稳定性分析 50-51 2.7.3 含软弱夹层的纯粘性土边坡稳定性分析 51-53 2.7.4 多级边坡稳定性分析 53-54 2.8 结论 54-55 3 三种水位下降模式下边坡稳定强度折减有限元分析 55-86 3.1 引言 55-56 3.2 非饱和非稳定渗流条件下边坡稳定分析的理论基础与数值实施 56-58 3.2.1 非饱和非稳定渗流分析 56 3.2.2 考虑基质吸力影响的强度折减技术 56-57 3.2.3 边坡稳定强度折减有限元法数值实施方法 57-58 3.3 流固耦合有限元计算理论基础与数值实施 58-60 3.3.1 考虑静水压力的多孔介质静力平衡方程 58 3.3.2 连续性方程 58-59 3.3.3 有限元计算 59 3.3.4 abaqus中有限元数值实施 59-60 3.4 水位骤降和缓将模式下边坡稳定性分析 60-65 3.4.1 库水位下降的三种模式 60-61 3.4.2 水位骤降与缓降条件下边坡稳定性分析 61 3.4.3 水位骤降与缓降条件下边坡算例分析 61-62 3.4.4 库水位缓降条件下土坡稳定性分析 62-63 3.4.5 库水位骤降条件下土坡稳定性分析 63-64 3.4.6 库水位骤降与缓降条件下边坡安全系数对比分析 64-65 3.5 简化非饱和非稳定渗流条件下土坡稳定性分析 65-66 3.6 非饱和非稳定渗流条件下土坡稳定性分析 66-72 3.6.1 坡体内最终浸润线的确定 67-68 3.6.2 渗透系数对边坡安全系数的影响 68-69 3.6.3 水位下降速率对边坡安全系数的影响 69-71 3.6.4 水位下降比对边坡安全系数的影响 71-72 3.6.5 考虑基质吸力影响的边坡稳定性分析 72 3.7 图表法在涉水边坡中的应用 72-81