岩质边坡稳定性分析中极限平衡法与有限元法的对比

根据工程实例 ,对一公路岩质边坡稳定性采用极限平衡法与有限元法分别进行计算 ,对比二者之间的差异 ,分析产生差异的原因。在安全系数的选用上提出了建议。     

基于点稳定系数法的斜坡稳定性分析

基于莫尔-库伦强度理论构架,界定了点稳定系数的概念,并推导其计算公式。利用Geostudio软件建立了均质斜坡模型及计算其应力分布,并在此基础上结合MATLAB软件计算斜坡模型中各点的点稳定系数,勾绘出斜坡体内不同稳定度区域,探析了斜坡稳定性,并与传统极限平衡法进行了对比。对比结果表明:对直立斜坡,两种方法的计算结果均为不稳定,但点稳定性系数法勾绘出坡脚及坡脚底部存在两处不稳定区域;对60°斜坡,点稳定系数法的计算结果表明坡脚处存在潜在不稳定区域,而极限平衡法的计算结果表明坡体处于稳定状态;对45°斜坡,两种方法的计算结果均为稳定,计算结果一致。进一步分析得到结论:点稳定系数法不需要假设或指定某一形状滑面进行斜坡稳定性评价,且可考虑应力集中对坡体稳定性的影响;极限平衡法以稳定系数表达计算结果,而点稳定系数法以不稳定区域表达计算结果。在分析了应力和岩土体力学参数因素对点稳定系数法计算结果的敏感性后发现:相对于极限平衡法,岩土体力学参数对点稳定系数法影响更为敏感,存在黏聚力界限点和内摩擦角界限点,且对均质斜坡破坏形式(局部滑动变形破坏或整体压缩变形破坏)起着非常重要的作用。     

有限元法在边坡稳定性评价中的应用

本文以瓦房店核联合泵房边坡为背景,在综合考虑地震地质因素的基础上,采用有限元法对该边坡稳定性进行了分析计算和评价,为该工程边坡设计提供了科学依据。     

GIS在边坡有限元数值分析前处理中的应用

有限元数值分析是边坡稳定性研究中较为常用的定量分析方法,但有限元分析的前处理工作通常比较繁琐,从而影响了该方法的整体工作效率。利用GIS软件实现了从计算剖面确定、计算剖面自动绘制到网格自动剖分的全部前处理过程。有效提高了边坡有限元计算的前处理工作效率,同时也提高了计算剖面图的科学性和边坡评价的准确性。     

石头坪景区边坡几何形态对稳定可靠度的影响分析

兰州金城公园石头坪景区提升改造工程存在大量的自然边坡和人工边坡。因边坡土体物理力学参数存在变异性,采用了蒙特卡洛随机抽样法和极限平衡法按不同坡高及坡度计算分析了边坡稳定可靠性指标及其变化规律,结果表明在景区实际坡高、坡度范围内边坡是稳定可靠的,适宜景区建设,但当坡高、坡度达到实际范围的最大值或超范围时,边坡处于基本稳定或欠稳定状态,建议采取加固措施。     

基于强度折减法的韩城煤矿边坡稳定性分析

将有限元强度折减理论应用于边坡稳定性分析中,运用ANSYS大型有限元分析软件,基于Drucker-Prager（D-P）屈服准则,采用力和位移的收敛标准作为破坏判据,进行边坡的稳定性分析。当折减系数达到某一数值时,非线性有限元静力计算将不收敛,滑面上的位移将产生突变,边坡内一定幅值的广义剪应变自坡底向坡顶贯通,此时认为边坡已破坏,并定义此时的折减系数即为稳定系数。文中以韩城煤矿节理岩质边坡为例,运用该方法进行了稳定性分析并与并与传统的Bishop法、Janbu法等方法对比。计算结果表明,有限元强度折减法能更加真实地反映边坡的实际情况,求得的边坡稳定系数更接近边坡的实际稳定状态,显示出其在边坡稳定性分析中的一定优势。     

基于有限元修正节理岩质边坡稳定性计算的解析解

采用有限元方法探讨在人工开挖或自然侵蚀环境下,岩质边坡体内应力场的变化及节理发育形成机理,并采用有限元强度折减法对后缘具有张节理边坡的稳定性影响因素进行敏感性对比分析,进而得出具有非贯通节理边坡稳定性计算的修正解析解。结果表明：卸荷及风化作用导致边坡体由表及里出现应力重分布及应力集中的现象,使边坡后缘由顶部向下发育一簇竖直向下或略向临空面倾斜的张节理,当张节理与下部的缓倾剪节理贯通时,边坡发生破坏;边坡稳定性最敏感的影响因素为受剪节理的倾角及贯通度,其次是节理的强度参数;可将工程中较难调查的节理贯通度转化为节理的强度参数来等效表达,并根据Mohr-Coulomb强度准则推导得到适用于具有非贯通节理的岩质边坡稳定性的修正解析解。     

岩质高边坡稳定性有限元分析

在评价边坡稳定性方面，采用弹性本构模型的有限元法是一种值得信赖的方法，它在诸多方法中能简便的处理复杂情况下岩土体边界和地质条件。本文介绍了有限元法边坡稳定性分析基本原理，并结合具体针对玉环高边坡区域构造特征和边坡的工程地质特征，应用有限元法建立了有限元模型及选取参数，进行了稳定性分析，得出了位移圉、应力图、安全系数图，定量的揭示和模拟边坡破坏、变形的过程和机制，并对边坡加固进行了可行的论证和建议。     

边坡稳定分析中瑞典条分法的改进

边坡稳定分析中常用的方法有极限平衡法和有限元法,而瑞典条分法由于其原理简明、公式简单而成为应用广泛的边坡稳定分析方法之一。但瑞典条分法忽略了土条侧面的作用力,并不能满足所有的平衡条件,由此算出的稳定安全系数比其他严格的方法偏低。本文是基于瑞典条分法做了适当的改进研究,从而提高了其计算精度。     

Cut Slopes in Clayey Soils: Consolidation and Overall Stability by Finite Element Method

When a cut slope in a saturated clay is undertaken, a transient water flow occurs and stress transferences from the water to the soil skeleton take place in time (consolidation). Mainly in strongly overconsolidated clays, these stress transferences may determine swelling of soil and therefore reduction of its shear strength in time. However, the lowering of the water level associated to the cut increases effective mean stress, which may therefore counterbalance the above-mentioned effect. In the paper, the behaviour of a cut slope in an overconsolidated clay is analysed by a finite element program that incorporates the Biot consolidation theory (coupled analysis), with constitutive relations simulated by the p–q–θ critical state model. In addition, the variation in time of the overall stability is assessed with a computer program that uses the finite element results and formulations of the critical state soil mechanics. In order to achieve a more complex geotechnical interpretation of the problem, the analysis in time of the excess pore pressures, effective stresses, displacements and stress levels is also presented. Finally, comparisons of stability results are analysed by changing some parameters, namely the problem geometry (weight of excavated soil) and the over-consolidation ratio of the clay.     

Improved Bell's method for the stability analysis of slopes

A new procedure based on the approximation to the total normal pressure along the slip surface is developed to compute the factor of safety of slopes for slip surfaces of all shapes. By taking the whole sliding body, instead of an individual slice, as the loaded object, all the equilibrium equations are formulated according to the three‐moment equilibrium conditions rather than the two force equilibrium conditions and one‐moment equilibrium condition. The system of nonlinear equations deduced in this way is well‐scaled and enjoys excellent numerical properties such as the existence of solution with a positive factor of safety, a nearly unlimited scope of convergence and a rapid convergence rate associated with the Newton method. In the case of ?_u =0—the situation where no drainage and no consolidation are involved, furthermore, the system has a unique solution and the factor of safety has an explicit expression. Some typical examples are analyzed to demonstrate the numerical properties of the proposed procedure. Copyright © 2009 John Wiley & Sons, Ltd.     

地震作用前后极限平衡法和强度折减法的边坡稳定分析对比

分别运用极限平衡法和ANSYS强度折减法对国内某边坡地震作用前后稳定性进行了分析,考虑地震作用时采用了拟静力法施加水平和垂直两个方向的地震力.根据地震作用前后两种方法得到的边坡稳定系数、滑动面、滑动体的对比分析发现,两种方法得出的安全系数、滑动面相差不大,说明了强度折减法运用到边坡稳定分析中是合理的.强度折减法得出安全系数均比极限平衡法略大,这是由于强度折减法考虑了土体的应力-应变关系,使得计算结果更符合实际.通过地震作用前后边坡的水平位移图的对比,总结了一些规律,为地震区边坡的锚固提出相应的建议.     

用有限元极限平衡法分析边坡的稳定性

用有限元分析为基础的极限平衡法计算了边坡安全系数,并将结果与摩尔-库仑屈服准则、外接圆D-P屈服准则强度折减法得到的结果、以及Spencer（极限平衡）法的结果进行了比较,结果表明,有限元极限平衡法计算的边坡安全系数与摩尔-库仑屈服准则强度折减法和Spencer法的结果很一致,而D-P准则强度折减法得到的结果偏差较大。叙述了存在已知滑动面和不存在滑动面时有限元极限平衡法的计算方法。用大型通用有限元软件,如ANSYS等,可方便地进行这种方法的边坡安全系数的计算,并有足够的精度。     

边坡稳定计算斜条分法机理分析

利用较严格的通用条分法的分析思路,将边坡条块划分一般化,即采用斜条分法。重新建立了斜条分法的各种平衡方程式,并在此基础上假定斜条块间切向力与法向力满足Mohr-Coulomb准则的函数关系。算例分析表明该方法所求的安全系数与通用条分方法的结果相近,得到的简化计算是可行的。     

确山盘龙废弃采坑边坡稳定性评价

以确山盘龙废弃采坑边坡为例,分别采用赤平极射投影法与极限平衡法从定性与定量的角度对采坑岩质边坡进行稳定性分析,再综合两种分析结果得出评价结论,提高了边坡稳定性评价的时效性和准确性。     

Improved finite element–based limit equilibrium method for slope stability analysis by considering nonlinear strength criteria and its application in assessing the anchoring effect

The shear strength envelope of most geotechnical materials is nonlinear. In this study, the finite element–based limit equilibrium method (FELE) is improved to assess the stability of a prescribed slip surface that obeys a nonlinear failure criterion. Two nonlinear failure criteria, namely, the Barton criterion and the generalized Hoek-Brown (GHB) criterion, are implemented. A power curve model that can perfectly fit the envelope of the GHB criterion is proposed to explicitly express the shear strength from the normal stress. The algorithm of the improved FELE, which includes a nonlinear criterion, is explained in detail, and the fast convergence of the method is checked by evaluating examples. The numerical examples show that, for a smooth slip surface, FELE can calculate a greater factor of safety (FOS) than that calculated using the Morgenstern-Price (MP) method when the strength criterion of slip surface is nonlinear. In addition, FELE can determine the bell-shaped distribution of the increase in normal stress caused by anchoring measures, which cannot be considered in the MP method.     

可靠度方法在边坡稳定性分析中的应用

可靠性工程是一门正在迅速发展的新学科,可靠度分析方法被看作近代工程技术的重要发展。通过可靠度分析方法对某边坡进行稳定性分析,并与传统的确定性分析方法对比。可靠度分析方法在边坡稳定性计算中具有实用性。     

EXCEL在边坡稳定性分析中的应用

利用Excel强大的数据处理、便捷的公式函数和所支持的面向对象化的程序设计语言VBA,应用于土坡的稳定性分析。基本方法为：先采用传统的瑞典条分法对边坡进行计算分析,在求得最危险滑动面的基础上,通过简化Bishop法对边坡安全系数Fs进行改进。在此过程中,Excel加载VBA子程序可以方便地得到极限平衡条分法中的各未知量,并计算出最危险滑动面上的安全系数Fs,同时使用其可视化功能绘出最危险滑动面的位置。此方法简化了计算程序,不仅容易在Excel表格中实现,且计算对比表明本文方法计算结果与简化Bishop法计算结果非常接近,可满足工程需要。     

Analysis of Critical Excavation Depth for a Jointed Rock Slope Using a Face-to-Face Discrete Element Method

Summary The critical excavation depth of a jointed rock slope is an important problem in rock engineering. This paper studies the critical excavation depth for two idealized jointed rock slopes by employing a face-to-face discrete element method (DEM). The DEM is based on the discontinuity analysis which can consider anisotropic and discontinuous deformations due to joints and their orientations. It uses four lump-points at each surface of rock blocks to describe their interactions. The relationship between the critical excavation depth D _s and the natural slope angle α, the joint inclination angle θ as well as the strength parameters of the joints c _r ,φ _r is analyzed, and the critical excavation depth obtained with this DEM and the limit equilibrium method (LEM) is compared. Furthermore, effects of joints on the failure modes are compared between DEM simulations and experimental observations. It is found that the DEM predicts a lower critical excavation depth than the LEM if the joint structures in the rock mass are not ignored.     

库水位变化对库岸边坡稳定性的影响

在假定坡体孔隙水水位为水平线且不考虑渗透作用影响的基础上,基于极限平衡法考察了水位上升及下降的快慢对边坡安全系数的影响。对比计算表明:在水位缓慢变化即坡体内外水位线等高的条件下,边坡的安全系数随着水位坡高比的增大先略减小后急剧增大,且在水位坡高比为0.3处取得最小值,在边坡完全淹没于水中时取得最大值。当边坡完全淹没于水中后,水位高于坡顶的多少对边坡安全系数没有影响;在水位骤降或陡升条件下,相同库水位对应的边坡安全系数基本上均小于水位缓慢变化情况下的安全系数,故工程实际中无论是排水还是蓄水,都应尽量保持水位缓慢变化,这样才能使边坡处于较安全的状态。