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1.
The influence of heterogeneity of undrained shear strength on the performance of a long slope cut in clay is investigated. Random field theory is used to model the heterogeneity and finite elements are used to compute the slope response. These have been used within a Monte Carlo simulation to compute reliability as a function of global factor of safety. It is shown that three failure modes are possible, depending on the ratio of the horizontal scale of fluctuation to the slope size, as characterised by its height and length. For very small values of this ratio, the slope fails along its entire length and the result is similar to a conventional 2D analysis based on the mean strength. For intermediate values, discrete failures are likely and reliability is a function of slope length. For large values of the ratio, the variability takes on a layered appearance and the result is equivalent to a 2D stochastic analysis. The validity of the boundary conditions is examined by analysing slopes of different length. It is shown that simple probability theory may be linked with stochastic analysis and finite elements to give efficient solutions for some large 3D problems. 相似文献
2.
Modeling uncertainty in stability analysis for design of embankment dams on difficult foundations 总被引：2，自引：0，他引：2
A probabilistic 3-D slope stability analysis model (PTDSSAM) is developed to evaluate the stability of embankment dams and their foundations under conditions of staged construction taking into consideration uncertainty, spatial variabilities and correlations of shear strength parameters, as well as the uncertainties in pore water pressure. The model has the following capabilities: (1) conducting undrained shear strength analysis (USA) and effective stress analysis (ESA) slope stability analysis of staged construction, (2) incorporation of field monitored data of pore water pressure, and (3) incorporation of increase of undrained shear strength with depth, effective stress, and pore water pressure dissipation. The PTDSSAM model is incorporated in a computer program that can analyze slopes located in multilayered deposits, considering the total slope width.
The main outputs of the program are the geometric parameters of the most critical sliding surface (i.e., center of rotation/radius of rotation and critical width of failure), mean 2-D safety factor, mean 3-D safety factor, squared coefficient of variation of resisting moment, and the probability of slope failure. The program is applied to a case study, Karameh dam in Jordan. Monitored data of induced pore water pressure in the dam embankment and soft foundation were gathered during dam construction.
The stability of Karameh dam embankment and foundation was evaluated during staged construction using deterministic and probabilistic analysis. Foundation stability was evaluated based on the monitored data of pore water pressure.
The study showed that the mean values of the corrective factors which account for the discrepancies between the in situ and laboratory-measured values of soil properties and for the modeling errors have significant influence on the 2-D safety factor, 3-D safety factor, slope probability of failure, and on the expected failure width.
The degree of spatial correlation associated with shear strength parameters within a soil deposit also influences the probability of slope failure and the expected failure width. This correlation is quantified by scale of fluctuation. It is found that a larger scale of fluctuation gives an increase in the probability of slope failure and a reduction in the critical failure width. 相似文献
3.
The undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able to account for the observed variation of undrained strength with loading direction. The model is able to encompass the different strength distributions observed in normally, slightly overconsolidated and heavily overconsolidated soils. A series of stability analyses have been performed to explore the effect of the type of undrained strength anisotropy on the stability and failure mechanisms of slopes of different inclinations. In addition, a real case study of the failure of an underwater slope is analysed with the numerical approach presented. It suggests that, by considering undrained strength anisotropy, the failure can be satisfactorily explained. 相似文献
4.
边坡可靠度分析中通常假定采用平稳或准平稳随机场表征土体参数的空间变异性,然而大量现场试验数据表明,土体参数如不排水抗剪强度沿土体埋深常呈现明显的非平稳分布特征,即其均值和标准差均随埋深发生变化,因此亟需发展土体参数非平稳随机场模型及其模拟方法。针对目前不能有效单独模拟土体参数趋势分量和随机波动分量的不确定性,提出了一种有效的不排水抗剪强度参数非平稳随机场模型,并给出了土体参数二维非平稳随机场模拟方法计算流程,同时将新提出的模型与现有非平稳随机场模型及平稳随机场模型进行了系统比较。最后通过不排水饱和黏土边坡算例验证了提出模型的有效性,并揭示了不排水抗剪强度非平稳分布特征对边坡可靠度的影响规律。结果表明：提出模型能够有效地单独模拟土体参数趋势分量和随机波动分量的不确定性,考虑土体参数均值和标准差随埋深增加而增大的特性,可为表征土体参数非平稳分布特征提供了一条有效的途径。此外,与采用非平稳随机场模拟土体参数空间变异性相比,采用常用的平稳随机场模型会低估边坡失效概率,从而造成偏危险的边坡工程设计方案。 相似文献
5.
6.
提出基于非侵入式随机有限元法的边坡可靠度分析方法,并编写计算程序NISFEM。采用有限元滑面应力法计算边坡安全系数,将Hermite随机多项式展开与SIGMA/W和SLOPE/W模块有机结合实现边坡可靠度非侵入式随机分析。根据随机多项式展开系数,给出边坡安全系数前4阶统计矩（均值、标准差、偏度和峰度）和Sobol指标解析表达式,并采用Sobol指标进行边坡可靠度参数敏感性分析。最后,以均质土坡可靠度问题为例,证明该方法在边坡可靠度分析中的有效性。结果表明,边坡可靠度分析的非侵入式随机有限元法能够有效地考虑边坡变形对边坡可靠度的影响,计算效率远远高于蒙特卡罗模拟方法（MCS）,是解决复杂边坡可靠度问题一种有效地分析手段;黏聚力和内摩擦角变异性对边坡安全系数前四阶统计矩具有明显的影响,重度变异性对安全系数前4阶统计矩几乎没有影响;抗剪强度参数间负相关性对边坡安全系数均值几乎没有影响,但对安全系数标准差、偏度和峰度均有明显的影响。此外,随着抗剪强度参数间负相关性的增加,边坡安全系数由近似正态分布逐渐变为明显的非正态分布。 相似文献
7.
考虑强度各向异性的边坡稳定有限元分析 总被引：1，自引：0，他引：1
天然沉积的土层总是表现出一定程度的强度各向异性,但现有的边坡稳定有限元分析极少考虑各向异性的影响。对大型有限元软件ABAQUS进行二次开发,使其能够考虑土体黏聚力随大主应力方向的变化,动态更新增量迭代求解过程中边坡不同位置处的抗剪强度,进而提出具备安全系数自动搜索功能的各向异性边坡稳定分析方法。计算结果表明,均匀边坡的有限元解与极限分析上限解相差很小。如果采用土体固结方向的黏聚力并按各向同性评价缓坡的稳定性,可能严重高估安全系数,尤其是在黏聚力较高的情况下。与极限分析不同,建立的强度更新有限元模型能够分析成层边坡的稳定性。 相似文献
8.
Subha Sankar Chowdhury 《Geotechnical and Geological Engineering》2017,35(6):2705-2714
The present study deals with the reliability analysis of basal heave caused by excavation considering uncertainty in the soil properties. The case study considered in the present work has been analyzed deterministically by Hsieh et al. (Can Geotech J 45:788–799, 2008). Taiwan building code is adopted in the method for analyzing the basal heave failure. The random variables (undrained shear strength and total unit weight of clay) are assumed to be normally distributed and uncorrelated. A series of parametric studies have been conducted to calculate the reliability index on the basis of the matrix formulation for the second moment method by Hasofer and Lind (J Eng Mech ASCE 100(1):111–121, 1974) considering different coefficient of variation of undrained shear strength and total unit weight of clay layers. It has been found that for a particular value of coefficient of variation of total unit weight, the reliability index with respect to occurrence of basal heave failure decreases with increase in the coefficient of variation of undrained shear strength. Moreover, the reliability index also decreases when the coefficient of variation of total unit weight increases. It has also been found that the probability of basal heave failure is lower with respect to factor of safety equals to 1.2, as compared to factor of safety equals to 1.0. Sensitivity analysis shows that the undrained shear strength of the bottommost layer and total unit weight of the second layer are the most significant random variables affecting the reliability index. Guidelines are provided for reliability based design where, for ‘target’ reliability index of 2.5 and 3.0, the factor of safety can be chosen such that all the related uncertainties are taken into account, especially with regard to undrained shear strength of the bottommost layer and total unit weight of the second layer. Design guidelines have been provided for this purpose. 相似文献
9.
The undrained tunnel face stability in clay with a linearly increasing shear strength with depth was investigated by three-dimensional finite element analysis. Three parametric studies were performed to study the effects of the cover depth ratio, overburden stress factor and linear strength gradient ratio on the load factor of the undrained tunnel face stability. The influence of the linear strength gradient ratio on the predicted failure mechanism of the undrained face stability was discussed and examined. An approximate closed-form solution was proposed for three-dimensional undrained tunnel face stability in clays with constant or linearly increasing shear strength profiles with depth. 相似文献
10.
在岩质边坡的稳定性计算分析中,各向异性岩体抗剪强度参数的合理取值直接决定了分析成果的可靠性。为充分考虑岩体各向异性对边坡工程的影响,本文基于H-B强度准则,利用边坡岩体质量分类体系CSMR替代RMR,对参数mb、s进行修正,并由此进一步计算得到各向异性边坡岩体的等效M-C强度参数。通过工程实例,计算比较了金沙江某水电站导流洞出口边坡在相同基岩条件、不同开挖设计方案下强度参数修正前后的边坡稳定安全系数。研究结果表明,岩体各向异性对边坡稳定性影响较大,未考虑岩体各向异性的岩体参数用于边坡稳定性计算时不能准确反映边坡的实际稳定性状态;而经过各向异性修正后,导流洞出口边坡两种设计方案下的整体稳定安全系数计算结果分别为1.11和1.70,与工程地质定性、半定量评价结果基本相符。通过本文提出的方法对边坡各向异性岩体参数进行修正,并在此基础上对边坡整体稳定性进行计算分析是可行的。 相似文献
11.
交变载荷作用下边坡的安定性分析 总被引：4，自引：1，他引：3
边坡稳定的极限分析方法只适用于比例加载的情况。当其上所受到的全部或部分载荷发生往复变化时,应该采用安定分析来评价边坡的安全性。通常边坡除了受到恒定的重力作用以外,地下水的作用也是一个不能忽视的因素。而由于降雨等原因,地下水位往往会在一定范围内往复变化,使得在稳定的地下水位以上的部分岩土体经常处于干湿循环的状态。根据率形式的Koiter机动安定定理,提出了考虑地下水位往复变化情况的边坡安定上限分析方法。利用抗剪强度参数折减定义的安全系数,定量地计算载荷变化对边坡稳定性的影响。最后通过一个直立边坡的简单算例证明了提出的分析方法的有效性。 相似文献
12.
《地学前缘(英文版)》2018,9(6):1657-1664
A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional(3 D) analysis when dealing with slope with full randomness in soil properties. Although 3 D random finite element analysis can well reflect the spatial variability of soil properties, it is often time-consuming for probabilistic stability analysis. For this reason, we also examined the least advantageous(or most pessimistic) cross-section of the studied slope. The concept of"most pessimistic" refers to the minimal cross-sectional average of undrained shear strength. The selection of the most pessimistic section is achievable by simulating the undrained shear strength as a 3 D random field. Random finite element analysis results suggest that two-dimensional(2 D) plane strain analysis based the most pessimistic cross-section generally provides a more conservative result than the corresponding full 3 D analysis. The level of conservativeness is around 15% on average. This result may have engineering implications for slope design where computationally tractable 2 D analyses based on the procedure proposed in this study could ensure conservative results. 相似文献
13.
基于Bootstrap抽样技术提出了有限数据条件下边坡可靠度分析方法。简要介绍了传统的边坡可靠度分析方法。采用Bootstrap方法模拟了抗剪强度参数概率分布函数的统计不确定性。以无限边坡为例研究了抗剪强度分布参数和分布类型不确定性对边坡可靠度的影响规律。结果表明：基于有限数据估计的样本均值、样本标准差和AIC值具有较大的变异性,这种变异性进一步导致了抗剪强度参数概率分布函数存在明显的统计不确定性。在考虑抗剪强度参数概率分布函数的统计不确定性时,边坡可靠度指标应为具有一定置信度水平的置信区间,而不是传统可靠度分析中的固定值。边坡可靠度指标的置信区间变化范围随安全系数的增加而增大,同时考虑分布参数和分布类型不确定性计算的可靠度指标具有更大的变异性和更宽的置信区间变化范围。Bootstrap方法为有限数据条件下抗剪强度参数概率分布函数统计不确定性的模拟以及边坡可靠度的评估提供了一条有效的途径。 相似文献
14.
Pressure-grouted soil nails have been increasingly used for stabilizing slopes. The pullout resistance of a soil nail is the main factor for reinforcing the slope stability. In this study, a two-dimensional axisymmetric finite element model is developed to simulate the pullout behavior of a pressure-grouted soil nail. This model is verified with field pullout tests result of a pressure-grouted soil nails by comparing with gravity-grouted soil nails. Based on the analysis, a three-dimensional finite element model is proposed for stability analysis of a slope reinforced with pressure-grouted soil nails using the shear strength reduction method. A series of numerical slope stability analyses for a slope composed of weathered soil are performed to investigate the effects of grouting pressure on the slope stability and the behavior of the soil nails. Special attention is given to the installation effect of a pressure-grouted soil nails. It is found from the result of this study that the pressure-grouted soil nails increase the safety factor by fifty percent in a slope by increasing the stiffness of the nailed slope system. Numerical analysis results confirm the fact that the pullout resistance of a soil nail is the main factor for stabilizing slopes rather than the shear resistance of the soil nail. 相似文献
15.
结合岩石节理面非线性Barton-Bandis破坏准则,探讨了将Barton-Bandis破坏准则参数转化为线性Mohr-Coulomb破坏准则抗剪强度参数的两种常用方法,通过实例分析了各方法的优劣。推导了加锚单岩石节理面控制的平面滑动岩体边坡抗滑稳定性安全系数计算式,开展了锚固参数分析。研究表明：相对于采用等效线性拟合法或切线等效法获取Mohr-Coulomb抗剪强度参数而言,直接应用Barton-Bandis破坏准则计算节理面控制的岩石边坡稳定性更为直观和简便;随着结构面基本摩擦角、结构面粗糙度系数和结构面壁面有效抗压强度的增大,边坡安全系数逐步提高,且结构面基本摩擦角和粗糙度系数对边坡安全系数的影响程度更为显著;锚索锚固力越大,边坡抗滑稳定性越好,而锚索设置角度越大,边坡抗滑稳定性越低,锚索角度设置不当将明显减小锚固效应的有效性。 相似文献
16.
岩土工程现场勘察试验通常只能获得有限的试验数据,据此难以真实地量化土体参数的空间变异性。提出了考虑土体参数空间变异性的概率反演和边坡可靠度更新方法,基于室内和现场两种不同来源的试验数据概率反演空间变异参数统计特征和更新边坡可靠度水平,并给出了计算流程。此外为合理地描述土体参数先验信息,发展了不排水抗剪强度非平稳随机场模型。最后通过不排水饱和黏土边坡算例验证了提出方法的有效性,并探讨了试验数据和钻孔位置对边坡后验失效概率的影响。结果表明：提出方法实现了空间变异土体参数概率反演与边坡可靠度更新的一体化,基于有限的多源试验数据概率反演得到的土体参数均值与试验数据非常吻合,明显降低了对参数不确定性的估计,更新的边坡可靠度水平显著增加。受土体参数空间自相关性的影响,试验数据对钻孔取样点附近区域土体参数统计特征更新的影响明显大于距离取样点较远区域。 相似文献
17.
《Computers and Geotechnics》2006,33(4-5):275-277
Conventional slope stability analysis is usually based on the linear Mohr–Coulomb failure criterion utilizing the notion of safety factors with respect to shear strength, and one of the available slice methods. Failure criteria of most soils are not linear, and it is possible to show that this non-linearity has a very significant effect on calculated safety factors. The present work is based on a non-linear failure criterion, which appears to fit the experimental information better than Mohr–Coulomb. All slice methods utilize various kinematical and static assumptions, which cannot be rationally justified. The present work is based on rigorous variational approach to slope stability analysis, which does not employ any kinematical and static assumptions. Safety factors with respect to shear strength are useful abstractions, but physical significance of results based on them is clear only at failure when they are equal to 1 (at any other value of the safety factor with respect to strength results of the analysis correspond to fictitious material with a modified shear strength function). In the present note, we use the variational analysis in order to establish a simple analytical relation between safety factors with respect to strength and height. These two safety factors provide alternative measures for the stability of a given slope; but the safety factor with respect to height appears to have clearer physical interpretation. 相似文献
18.
基于强度折减法的土石混合体边坡长期稳定性研究 总被引：1，自引：0，他引：1
土石混合体边坡是自然界中常见的一种边坡类型,具有明显的不均匀性和不连续性。土体的蠕变是造成土石混合体边坡变形及失稳的主要原因之一,而目前关于土石混合体边坡稳定性的研究几乎均未考虑土体的蠕变性。首先运用数字图像处理技术对我国某水电站库区的一个土石混合体边坡进行建模,而后利用FLAC3D软件中的强度折减法对其进行稳定性分析,并着重研究了土体的蠕变特征及其蠕变参数对土石混合体边坡变形及稳定性的影响。计算结果表明,土体的蠕变特征会明显降低土石混合体边坡的安全系数,增大边坡变形,进而对边坡的稳定性造成不利影响;其中蠕变黏性系数对边坡的长期稳定性具有较大影响,黏性系数越大,则土石混合体边坡的安全系数越低。 相似文献
19.
上限原理有限元法不仅可以得到边坡的安全系数,还可以给出临界滑动面,且具有比极限平衡法更严谨的理论基础,因此,拥有更广阔的应用前景。针对传统的上限有限元法不能考虑强度各向异性的问题,提出了一种新的摩尔-库仑屈服面线性化方法。该方法在对方位角离散化的基础上,建立了线性化的方位离散塑性流动约束方程,丰富了基于线性规划的上限法理论。两个算例结果表明：该方法可以稳定地从极限解的上方收敛;且对边坡进行稳定性分析,若忽略了边坡的强度各向异性,则会高估边坡的稳定性,得到较大的安全系数。 相似文献
20.
非饱和-非稳定渗流条件下的边坡临界滑动场 总被引：1，自引：0，他引：1
受季节性降雨或水库运行的影响,岸坡外水位及坡内孔隙水压力场的变化较大,不利于岸坡的稳定性。在水位变化过程中,利用非饱和-非稳定渗流有限元计算得到孔隙水压力场,基于非饱和土的渗流和抗剪强度理论,对水位变化过程中的边坡临界滑动场法进行改进,提出可考虑水位变化与岸坡非饱和-非稳定渗流过程的边坡临界滑动场数值模拟方法。将改进后的水位变化过程中的边坡临界滑动场法分别应用于黏土、粉土岸坡在水位升降过程中的稳定性分析,研究了水位升降速率及基质吸力对岸坡稳定性的影响,并揭示了边坡在水位变化过程中的稳定性变化历程。研究表明,该方法计算结果合理、可靠,更适用于涉水边坡的稳定性计算,且岸坡稳定性变化历程受水位升降速率、基质吸力等多种因素共同影响,只有在考虑非稳定渗流的基础上同时考虑基质吸力的作用才能正确得出水位变化过程中岸坡稳定性变化规律和实质。 相似文献