强度折减有限元在堤防稳定分析中的应用研究

采用强度折减有限元法,研究非均值堤防塑性区的开展特征和失稳破坏过程,并根据堤防应力场分布和临界滑动面的形成来分析堤岸整体失稳破坏的机理.结果表明:把强度折减有限元应用到非均质土层的堤防边坡稳定分析,在理论上、数值模拟实现上都是可行的;有限元静力平衡和位移计算不收敛作为堤防边坡整体失稳的标志,同时考察滑移面上某些特征点的...     

基于有限元计算的边坡三维滑裂面搜索

提出一种基于有限元计算的边坡三维滑裂面搜索的方法,根据有限元计算的应力结果,计算可能滑裂面的安全系数,然后用遗传算法搜索出最危险滑裂面,并得出相应的安全系数作为边坡的安全度评价指标。该方法的优越性是只需进行一次有限元计算,不需要假定滑裂面,可以用于具有复杂地貌和地质构造的三维边坡。通过算例,验证该方法的可行性和程序的正确性,以大岗山水电站库区边坡工程实例验证该方法的实用性。     

基于强度折减弹塑性有限元法的抗滑桩加固边坡稳定性分析

以大型通用有限元分析软件ABAQUS作为平台,以迭代不收敛联合坡面特征点位移陡增作为抗滑桩加固边坡失稳判据,通过二次开发建立了能够自动搜索安全系数的抗滑桩加固边坡稳定性强度折减弹塑性有限元分析模型,结合典型算例的对比分析验证了这一判据的有效性。在此基础上,针对一实例边坡进行了稳定性数值分析。研究表明,对于抗滑桩加固边坡,以强度折减有限元法所确定的潜在滑动面,一般地比极限平衡法、极限分析上限方法要浅。     

样条函数模拟土坡滑动面的效率分析

土坡稳定分析中,二维滑动面通常由一系列点顺序连接产生,并且将点的坐标当作优化变量来搜索临界滑动面,当点的个数较多时会导致优化变量较多;只需给定少量的控制节点,即可利用三次样条函数得到光滑的曲线作为任意滑动面,该法对于含软弱夹层土坡,无需事先指定直线段。利用不平衡推力法计算给定滑动面的安全系数,采取和声搜索算法确定最小安全系数相应的临界滑动面。对3个土坡算例进行了比较分析,比较了常规策略与样条函数方法在模拟土坡滑动面时的效率。     

地震动加速度幅值对土坡失稳后滑坡体大小及致灾范围的影响

地震滑坡的致灾范围是判断滑坡能否会对已有建构筑物造成损失、确定预警疏散范围的重要依据,因此对地震土坡破坏后的滑坡体大小和致灾范围进行研究具有重要的意义.本研究基于SPH动力分析方法,结合弹塑性本构模型和固体力学控制方程建立了地震土坡破坏的动力分析模型;通过设置振动边界粒子和自由场边界粒子,实现了地震动加速度的施加以及自...     

边坡变形破坏过程的大变形有限元分析

在用有限元法分析边坡稳定性时,引入计算大变形问题的更新的拉格朗日方法,推导了边坡大变形弹塑性有限元分析的方程式。采用边坡某一幅值的等效塑性剪应变区,从坡脚到坡顶贯通前的折减系数作为边坡安全系数。在此基础上,采用弹塑性大变形有限元分析软件计算了均质土坡不同坡角的安全系数,将其与小变形分析的结果进行了对比分析,结果表明：用弹塑性大变形有限元分析边坡失稳破坏的过程中,既考虑了岩土材料的非线性,又考虑了边坡的几何非线性,使计算结果更趋合理。并结合东深供水改造工程BIII2边坡进行了大变形有限元分析,计算结果与勘查到的实际边坡的滑动面分布位置比较接近。研究表明：该方法尤其适宜于软土类边坡或基坑的稳定性分析。     

Sensitivity analysis applied to slope stabilization at failure

This article discusses how sensitivity analysis is a sound assessment tool for selecting the most efficient stabilization method of slopes at failure. A discretized form of the variational approach is used not only for performing sensitivity analysis but to locate the critical slip surface, i.e., the sensitivity analysis is carried out in the same way as it is done in optimization problems. This method supplies a robust formulation and methodology for obtaining the sensitivities of the safety factor with respect to both the soil parameters and the slope profile, stating the slope stabilization design as a relatively simple minimization problem. Two well known examples, as the Selset landslide and the Sudbury Hill slip are used to illustrate the application of the method and to highlight both its capabilities and limitations.     

Numerical analysis on seepage failures of dike due to water level-up and rainfall using a water–soil-coupled smoothed particle hydrodynamics model

For seepage failures of dike due to water level-up and rainfall, surface infiltration and strength change induced by suction reduction are important factors; thus, numerical analysis should consider the coupling of water and soil, as well as the effect of saturation to obtain more precise failure mechanism. Based on the advanced smoothed particle hydrodynamics (SPH) method, this work proposed a two-phase-coupled SPH model in coordination with a novel constitutive model for unsaturated soils. Then, a triaxial compression test is simulated to check the applicability of the SPH method on the soil phase. After that, the failure test of a dike due to water level-up is discretized and simulated, from which the seepage process, the distribution of maximum shear strain, the slip surface, and pore water pressure are obtained. The two-phase-coupled SPH model is also applied to a slope failure test of heavy rainfall, and the results are compared to the model test. Finally, a dike failure test due to rainfall is analyzed using the proposed SPH model to reproduce the surface infiltration and suction reduction. The proposed SPH model provides several insights of seepage failures and can be a helpful tool for the analysis of dike failures induced by water level-up and rainfall.     

蒙特卡洛法与有限元结合搜索边坡临界滑动面

把蒙特卡洛随机搜索法与有限元法相结合,搜索边坡的临界滑动面及其对应的最小安全系数.通过随机跳跃法生成一定数量的初始试算滑动面,根据有限元分析的应力和孔隙水压力结果计算给定滑动面的安全系数,利用随机走步法不断更新试算滑动面,使试算滑动面安全系数不断减小,最终确定边坡临界滑动面及其对应的最小安全系数.本方法通过随机搜索,克服了大多数常规优化方法易陷入安全系数局部极小的问题.数值算例分析说明了本文提出的确定边坡临界滑动面的方法的有效性和优越性.     

基于遍布节理模型的边坡稳定性强度折减法分析

采用非线性数值分析方法分析边坡稳定性问题时,强度折减法因其具有较多的优点而得到广泛应用。岩土体一般采用理想弹塑性模型,屈服准则为广义米赛斯准则。对于密集节理岩质边坡稳定性问题,采用遍布节理模型可同时考虑岩块和节理属性,更符合岩体状态及工程实际,认为岩体经强度折减后潜在破坏可能首先出现在岩体中或沿节理面或二者同时破坏。结合工程实例,基于遍布节理模型的强度折减法计算结果表明,潜在滑移面为折线型滑面,下部潜在滑移面倾角与节理面等效内摩擦角基本一致,上部潜在滑移面与岩体拉破坏相关;节理倾角与边坡安全系数、潜在滑动范围密切相关,陡倾角节理对边坡稳定性影响较小。通过对边坡失稳判据和边坡滑移面确定的探讨,认为以力或位移不收敛作为边坡失稳判据是适当的,而边坡的剪应变速率物理意义十分明确,适于作为边坡潜在滑移面的确定依据。     

Numerical SPH analysis of debris flow run-out and related river damming scenarios for a local case study in SW China

A smoothed particle hydrodynamics (SPH) numerical modeling method implemented for the forward simulation of propagation and deposition of flow-type landslides was combined with different empirical geomorphological index approaches for the assessment of the formation of landslide dams and their possible evolution for a local case study in southwestern China. The SPH model was calibrated with a previously occurred landslide that formed a stable dam impounding the main river, and it enabled the simulation of final landslide volumes, and the spatial distribution of the resulting landslide deposits. At four different sites on the endangered slope, landslides of three different volumes were simulated, respectively. All landslides deposited in the main river, bearing the potential for either stable impoundment of the river and upstream flooding scenarios, or sudden breach of incompletely formed or unstable landslide dams and possible outburst floods downstream. With the empirical indices, none of the cases could be identified as stable formed landslide dam when considering thresholds reported in the literature, showing up the limitations of these indices for particular case studies of small or intermediate landslide volumes and the necessity to adapt thresholds accordingly for particular regions or sites. Using the occurred benchmark landslide as a reference, two cases could be identified where a complete blockage occurs that is more stable than the reference case. The other cases where a complete blockage was simulated can be considered as potential dam-breach scenarios.     

Probabilistic analysis of simple slopes with cohesive soil strength using RLEM and RFEM

The 2D random finite element method and the one-dimensional and 2D random limit equilibrium method are used to investigate the influence of spatial variability of soil strength parameters on the probability of failure of simple soil slopes with cohesive undrained shear strength. The combined influence of spatial variability of soil properties and cross-correlation between undrained soil strength and unit weight on the computed probability of failure is explored. The paper identifies conditions where numerical outcomes are similar and where they are not. The limitations of each analysis method are described and implications to analysis and design are identified.

Abbreviations: FEM: finite element method; LEM: limit equilibrium method; RFEM: random finite element method; RLEM: random limit equilibrium method     

基坑土钉支护可靠性分析优化算法

针对基坑工程中岩土参数存在随机性和变异性的特点,基于响应面重构法、遗传算法和禁忌搜索方法研究了土钉墙边坡可靠性分析方法。考虑土钉的加固作用,建立了适用于土钉墙边坡任意形状滑面安全系数计算的改进Morgenstern-Price法。基于响应面原理,将改进Morgenstern-Price法取代传统响应面法中的有限单元法来随机抽样构造响应面函数,建立了一种近似的土钉墙边坡可靠度计算方法。以土体的抗剪强度指标 、 为随机变量,提出了一种能同时确定土钉墙边坡最小可靠度指标 及相应最危险滑面的全局优化计算方法--土钉墙可靠性分析自适应禁忌搜索遗传算法（ATSGA）。结合算例,分别以土钉墙边坡的最小可靠度指标和最小中值安全系数为目标函数,采用ATSGA法搜索其相应的最危险滑动面,结果表明,二者相差较大。     

Mechanism of the Anlesi landslide in the Three Gorges Reservoir, China

Many gentle dip translational rock slides have taken place in the Three Gorges Reservoir, China. In order to study the mechanism of these translational rock slides, the authors use the Anlesi landslide as a typical case study to investigate in detail. Field investigations show that the slip zones of the Anlesi landslide were formed from a white mudstone in Jurassic red strata. X-ray diffraction and infrared ray analysis showed that the main mineral components of the slip zones are montmorillonite, illite, feldspar and quartz. Laboratory tests indicate that the slip zone soils are silty clay, of medium-swelling potential, the shear strength decreasing significantly as the slip zone attracts water and saturates.The main factors contributing to the Anlesi landslide are recent tectonic activity, incompetent beds, and intensive rainfall. Recent tectonic activity had caused shear failure along the incompetent beds, and joints within the sandstone. With the effect of intensive rainfall, water percolates to the incompetent beds along tectonic fissures, resulting in swelling of the soil material and high groundwater pressures within fissures in the strata. As a consequence, the Anlesi slope is prone to slide along these incompetent beds.Flac3D software was used to simulate the mechanism of the Anlesi landslide considering the rheological properties of soil and rock. The simulation results demonstrate that the stress, displacement and failure area changes with simulated creep time. The maximum displacement in the X direction reaches 7.59 m after 200-year simulated creep. Therefore, the mechanism of the Anlesi landslide can be illustrated considering the rheological properties of Jurassic red strata.     

Identification of representative slip surfaces for reliability analysis of soil slopes based on shear strength reduction

Although a slope may have numerous potential slip surfaces, its failure probability is often governed by several representative slip surfaces (RSSs). Previous efforts mainly focus on the identification of circular RSSs based on limit equilibrium methods. In this paper, a method is suggested to identify RSSs of arbitrary shape based on the shear strength reduction method. Monte Carlo simulation is used to generate a large number potential slip surfaces. The RSSs are identified through analyzing the failure domains represented by these samples. A kriging-based response surface model is employed to enhance the computational efficiency. These examples shows that the RSSs may not always be circular, and that the suggested method can effectively locate the RSSs without making prior assumptions about the shape of the slip surfaces. For the examples investigated, the system failure probabilities computed based on the shear strength reduction method are comparable to, but not the same as those computed based on the limit equilibrium methods. The suggested method significantly extends our capability for identifying non-circular RSSs and hence probabilistic slope stability analysis involving non-circular slip surfaces.     

基于聚类分析的边坡稳定性研究

在边坡稳定性分析中,滑面搜索方法对于得到边坡的稳定性系数至关重要。现今两种常用的边坡稳定性分析方法,极限平衡法以及强度折减法,可以得到极限应力状态下边坡的潜在滑面。而为了评价边坡在当前应力场下的稳定性,提出一种基于聚类分析概念的滑面搜索方法。这种方法综合考虑了边坡各点的位移以及点安全系数,采用K均值聚类法将具有相近性质的点进行分类,把边坡体分为潜在危险区以及稳定区。潜在危险区的边界即为边坡在当前应力状态下的潜在滑面,并运用矢量和方法计算得到其稳定性系数。采用上述方法对3个算例进行验算,并与极限平衡法以及强度折减法进行对比。结果表明：（1）基于聚类分析的边坡稳定性评价方法具有较好的合理性和可靠性;（2）当边坡处于临界状态附近,通过聚类分析得到的潜在滑面与其他两种方法得到的滑面基本一致;当边坡处于较稳定状态时,当前应力状态下的潜在滑面要比强度折减法得到的滑动带范围要更深更广,但求出的稳定性系数也较高;当存在软弱夹层时,矢量和计算出的滑面更为陡峻,稳定性系数比其他两种方法的结果要小。     

鄂西北山区降雨型边坡失稳模式和评价方法

2003年6月的一次连续降雨诱发了鄂西北山区郧漫公路沿线多处边坡失稳。根据边坡岩土体的组成和结构特征,总结出了5种典型的暴雨型边坡失稳模式:浅层堆积体滑移、含软弱面顺层滑移、切层边坡水压劈裂破坏、碎裂岩似弧形追踪破坏和块裂岩楔体滑移。根据边坡破坏特点和降雨作用形式提出了相应的评价方法,认为浅层堆积体在暴雨下含水量,即85%~100%液限含水量时易发生滑移,通过平面无限斜坡评价法计算边坡稳定性;含软弱面顺层边坡及块裂楔形体均为剪切滑移失稳,采用简化的刚体极限平衡法计算其稳定性;切层边坡中陡倾裂缝经历了卸荷张开－水压开裂－贯通破坏的过程,通过Ⅰ型裂缝扩展判据评价边坡稳定性;碎裂岩边坡发生类似弧形滑移的追踪破坏,采用连续介质圆弧法计算边坡稳定性。     

Full probabilistic design of slopes in spatially variable soils using simplified reliability analysis method

ABSTRACT

A simplified reliability analysis method is proposed for efficient full probabilistic design of soil slopes in spatially variable soils. The soil slope is viewed as a series system comprised of numerous potential slip surfaces and the spatial variability of soil properties is modelled by the spatial averaging technique along potential slip surfaces. The proposed approach not only provides sufficiently accurate reliability estimates of slope stability, but also significantly improves the computational efficiency of soil slope design in comparison with simulation-based full probabilistic design. It is found that the spatial variability has considerable effects on the optimal slope design.     

基于坡面网格全局搜索土坡临界滑动面的优化技术

提出了一种基于坡面网格全局搜索土坡临界滑动面的综合优化方法。该方法较好地结合了几何优化和数值优化长 处,原理简单,若辅以一定的经验分析,能较高效地得到土坡临界滑动面。通过2个实例计算表明,该方法计算搜索结果具有较好的稳定性和完备性,并且适用于一些复杂的工程土坡。     

Numerical simulation of flow processes in liquefied soils using a soil–water-coupled smoothed particle hydrodynamics method

Liquefaction can result in the damage or collapse of structures during an earthquake and can therefore be a great threat to life and property. Many site investigations of liquefaction disasters are needed to study the large-scale deformation and flow mechanisms of liquefied soils that can be used for performance assessments and infrastructure improvement. To overcome the disadvantages of traditional flow analysis methods for liquefied soils, a soil–water-coupled smoothed particle hydrodynamics (SPH) modeling method was developed to analyze flow in liquefied soils. In the proposed SPH method, water and soil were simulated as different layers, while permeability, porosity, and interaction forces could be combined to model water-saturated porous media. A simple shear test was simulated using the SPH method with an elastic model to verify its application to solid phase materials. Subsequently, the applicability of the proposed SPH modeling method to the simulation of interaction forces between water and soil was verified by a falling-head permeability test. The coupled SPH method produced good simulations for both the simple shear and falling-head permeability tests. Using a fit-for-purpose experimental apparatus, a physical flow model test of liquefied sand has been designed and conducted. To complement the physical test, a numerical simulation has been undertaken based on the soil–water-coupled SPH method. The numerical results correspond well with the physical model test results in observed configurations and velocity vectors. An embankment failure in northern Sweden was selected so that the application of the soil–water-coupled SPH method could be extended to an actual example of liquefaction. The coupled SPH method simulated the embankment failure with the site investigation well. They have also estimated horizontal displacements and velocities, which can be used to greatly improve the seismic safety of structures.