基于最大剪应变增量的边坡潜在滑动面搜索

滑动面位置和形状的判断是影响边坡地基稳定性分析合理性的主要因素,合理地确定滑动面的位置和形状是边坡地基稳定性分析首先要解决的问题。由岩土工程常用的Mohr-Coulomb度理论可知,岩土体破坏是由于某一面上的剪应力达到了岩土体的剪切强度,此时剪切面上必然发生较大的剪切变形,因此可以通过搜索最大剪应变增量的位置来确定边坡滑动面。基于以上思路,综合运用有限差分软件FLAC3D和曲线拟合技术,提出基于最大剪应变增量确定边坡地基潜在滑动面的方法。首先,利用有限差分软件FLAC3D计算极限状态时边坡内的应力、应变,在计算剖面中设置一系列的垂线,利用FISH语言编制程序搜索垂线上剪应变增量最大位置的坐标,以获得滑动面上的离散点坐标。然后,通过最小二乘的方法对离散点进行曲线拟合,得到滑动面的形状和位置。通过与极限平衡法的对比分析,验证文中方法的合理性。文中方法的判断标准物理意义明确,简便实用,且克服了对网格的依赖性。     

基于离散元的重力坝多滑面深层抗滑稳定分析

重力坝的深层抗滑稳定分析多采用刚体极限平衡法和非线性有限元法,但刚体极限平衡法不能反映坝基岩体渐进失稳过程和破坏的力学机制,非线性有限元法模拟岩体不连续效率低,且还未有统一的失稳判据。基于离散块体边界应力计算结果,提出重力坝坝基多滑面抗滑稳定安全系数计算公式,并探讨了以坝体-坝基系统能量突变作为坝基失稳判据的物理意义。通过与非线性有限单元法、刚体极限平衡法计算结果的比较,验证了所提方法及判据的可靠性及合理性。结合向家坝水电站重力坝泄12#坝段进行计算分析,结果表明：基于离散元强度储备系数法搜索的坝基失稳通道由坝基岩体屈服区和结构面滑移带组成,所提计算方法与判据适用于实际工程的坝基深层抗滑稳定计算分析,且计算结果偏安全。     

Dynamic sliding of tetrahedral wedge: The role of interface friction

The role of interface friction is studied by slow direct shear tests and rapid shaking table experiments in the context of dynamic slope stability analysis in three dimensions. We propose an analytical solution for dynamic, single and double face sliding and use it to validate 3D‐DDA. Single face results are compared with Newmark's solution and double face results are compared with shaking table experiments performed on a concrete tetrahedral wedge model, the interface friction of which is determined by constant velocity and velocity stepping, direct shear tests. A very good agreement between Newmark's method on one hand and our 3D analytical solution and 3D‐DDA on the other is observed for single plane sliding with 3D‐DDA exhibiting high sensitivity to the choice of numerical penalty value. The results of constant and variable velocity direct shear tests reveal that the tested concrete interface exhibits velocity weakening. This is confirmed by shaking table experiments where friction degradation upon multiple cycles of shaking culminated in wedge run out. The measured shaking table results are fitted with our 3D analytical solution to obtain a remarkable linear logarithmic relationship between friction coefficient and sliding velocity that remains valid for five orders of magnitude of sliding velocity. We conclude that the velocity‐dependent friction across rock discontinuities should be integrated into dynamic rock slope analysis to obtain realistic results when strong ground motions are considered. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural stability of gravity dams: a progressive assessment considering uncertainties in shear strength parameters

Structural sliding stability of gravity dams is generally quantified using deterministic factor of safety, FS_det. Large FS_det (e.g. 3 in normal condition), are used in existing guidelines to guard against material and load uncertainties. Some guidelines allow an arbitrary reduction in FS_det (e.g. 2) when the knowledge in strength parameters increases from material test data. Yet, those reduced FS_det are not based on a rational consideration of uncertainties. Propagation of uncertainties could be done using probabilistic analyses, such as Monte-Carlo simulations (MC) which are complex and challenging for practical use. There is thus a need to develop simplified reliability based safety assessment procedures that could rationalise the adjustment of FS_det. This paper presents a progressive analysis methodology using four safety evaluation formats of increasing complexity: (i) deterministic, (ii) semi-probabilistic (partial coefficient), (iii) reliability based Adjustable Factor of Safety (AFS), and (iv) probabilistic. Comprehensive comparisons are made for the sliding safety evaluation of a 80 m gravity dam. Results are presented in terms of sliding factors of safety, allowable water levels, and demand/capacity ratios. It is shown that the AFS formulation, using direct integration, is simple and practical to use in complement to existing dam safety guidelines before undertaking MC simulations.     

3D modeling of stratified and irregularly jointed rock slope and its progressive failure

Little has been published on the three-dimensional (3D) simulation of the progressive failure of rock slopes, possibly because the process of failure involves a complex, nonlinear evolution from initiation, through propagation and crack. In addition, rock is typically anisotropic, which makes it difficult to identify and describe the slope constituents and failure processes accurately. Despite such difficulties, further study of the fracture process is just as important as analyzing stress fields in 3D rock slope failures. In this paper, the 3D realistic failure process analysis code using finite element programming, and an extended version of numerical centrifugal method, is used to simulate slopes failure with different dip angles. The numerical centrifugal analysis results in this paper are found that the critical failure surface develops along the weak structural surface when the slope dip angle β is below 30°; conversely, the failure surface is formed along the toe of circular sliding when β is above 30°. In addition, it is also found that whether or not including the irregularity of joint into modeling to analyze the 3D slope stability problem will lead to a significant difference in factors of safety, it can reach 8.41 % at the same slope angle. Furthermore, the acoustic emission analyzing reveals deformed location characters of rock slope during the failure processes. With such capabilities, the approach contributes significantly to the in-depth study of the mechanisms of rock slope instability process.     

基于分项系数法的重力坝深层抗滑稳定分析

针对基于有限元法的重力坝深层抗滑稳定分析问题,根据工程实际中软弱结构面上的抗剪断摩擦系数和凝聚力变异性不同的特点,在计算中引入滑动面上抗剪断强度参数的分项系数,提出了一种新的应用于重力坝抗滑稳定的有限元计算方法--分项系数有限元法。该方法基于可靠度思想,以达到用极限承载状态时的强度储备系数或超载系数来表征大坝安全度。在已有研究成果的基础上,从坝基渐进破坏过程和破坏机理的角度进一步探讨了非线性有限元法应用于深层抗滑分析应注意的几个关键问题,以及基于分项系数法的深层抗滑稳定分析的安全系数控制标准。研究结果表明,滑动面上的应力分布性态和坝基岩体变形特性对抗滑稳定安全系数有重要影响。与常规刚体极限平衡方法的控制标准相比,分项系数有限元方法可以采用偏低一点的安全系数标准。     

边坡岩土体抗剪强度的逆向迭代修正反演方法

针对已滑动或有明显变形的边坡,取定稳定系数值进行反演分析是确定岩土体抗剪强度的重要手段。当边坡滑动面穿越多层岩土体时,盲目地抗剪强度试算反演明显不合理。为解决此问题,构造以多层岩土体抗剪强度为输入,以GeoSlope计算得到的稳定系数、滑面剪入口和剪出口位置为输出的BP神经网络,基于取定的稳定系数和现场测定的滑动面剪入口和剪出口位置,通过重复执行“逆向反推-误差校验-样本修正”实现岩土体抗剪强度的逆向迭代修正反演。工程实例验证结果表明,该方法获取的岩土体抗剪强度基本合理,可供小型边坡防护工程设计参考。该方法成功地规避了BP神经网络以已知信息为输入、以待反演参数为输出的传统做法在解决该问题时为欠定的局限性,对样本库样本数量的要求降低且具有较好精度。     

连通节理岩质边坡稳定性分析

节理岩体的剪切强度由结构面和相邻完整岩块的剪切强度共同决定,当结构面完全连通时,岩体的剪切强度完全由结构面决定。蒙特卡罗法能够根据结构面几何参数模拟岩体结构面的空间分布,通过深度优先搜索算法可搜索到连通的结构面,相对岩体而言,连通的结构面的剪切强度最小,即为节理岩质边坡的潜在滑动面,通过极限平衡法可以对一系列滑面进行稳定性分析。该方法是对节理岩质边坡稳定分析的补充。     

基于可靠性理论抗滑桩设计体系的研究

抗滑桩设计的常规方法是建立在定值基础上的,未能考虑计算参数的随机性与变异性,故在抗滑桩设计中存在局限性：一是不能给出抗滑桩设计的边坡安全度;二是设计中过分保守,造成浪费。可靠性分析法考虑了计算参数的随机性,用严格的概率来度量边坡的安全度,弥补了上述传统抗滑桩设计中存在的不足。基于可靠性分析法,以传统边坡稳定性计算公式为基础,建立了抗滑桩设计的边坡稳定性评价模型,并且运用蒙特卡罗法,采用单参数敏感性分析方法,分析抗滑桩设计各参数对边坡安全系数及可靠性指标的影响。结果表明,岩土体抗剪强度参数、岩土体重度、抗滑桩直径等因素对可靠性指标影响较明显,边坡安全系数对岩土体重度、抗滑桩有效长度、抗滑桩直径等随机变量较敏感。     

Limiting equilibrium versus BS3D analysis of a tetrahedral rock block

In order to analyze the stability of a 3D rock block using a limiting equilibrium method, some simplifications must be introduced, such as neglecting the effects of deformability of the rock block, fractures, and the surrounding rock mass, the progressive failure and the mobilization of shear strength of fractures, and changes in in situ stresses with block displacement. These limitations may cause some errors when calculating the factor of safety of the block. This paper quantifies the error caused by these simplifications comparing the results against those obtained with a numerical method (BS3D). In addition, the effects of the normal stiffness of the fractures, dilatancy, the tunnel radius, and the block size on stability of the tetrahedron are investigated using the numerical tool to demonstrate the importance of the effects eliminated by the limiting equilibrium approach. Copyright © 2010 John Wiley & Sons, Ltd.     

似层状岩质边坡倾倒变形破坏过程数值模拟

在构造裂隙组合切割下形成的反倾向"似层状"结构边坡在工程中普遍存在。文章以浙江某梯级电站厂房后边坡为例,通过运用二维离散元和三维有限差分法,对"似层状"岩质边坡倾倒变形特征及破坏演化历程进行模拟,结果表明这类边坡变形破坏主要经历三个时期:初期为块体间的相互剪切错动和局部缓倾节理的剪切蠕变;中期岩体加剧倾倒后推动坡体前缘滑动,在坡体表面形成倾倒台阶后地表拉裂;后期倾倒变形剪切错动向坡体内部扩展,剪切带相互连通并逐步追踪缓倾结构面或强弱风化分界面,在空间形态上形成具有"台梯状分布"的滑动带,为深层蠕滑创造条件。     

花岗岩与混凝土胶结面抗剪强度的试验研究

坐落在基岩上的重力式建筑物（重力坝、悬索桥的锚碇等）,依靠基岩与大体积混凝土接触面的摩擦力平衡巨大的水压力或锚索拉力。接触面的摩擦系数有很小的变化,需要混凝土的体积发生大的变化保持摩擦力不变,从而工程造价出现大的差别。针对润扬长江公路大桥南汊悬索桥锚碇接触面抗剪强度取值问题,采用室内控制粗糙度试验的方法,测试了不同风化程度和粗糙度的花岗岩与混凝土接触面的抗剪强度。结合现场编录和现场粗糙度测试结果,获得了混凝土与基岩胶结面摩擦角的分区和面积加权平均值,为锚碇的稳定验算提供了准确的数据。试验结果对其它重力式抗滑结构设计有参考价值。     

The effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions

In this article, the effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions is investigated. For this purpose, four finite element models of dam–reservoir–foundation interaction system are prepared by using the Lagrangian approach. In these models, the reservoir length varies from H to 4H (H: the height of dam). The Folsom gravity dam is selected as a numerical application. Two different ground motion records of 1989 Loma Prieta earthquake are used in the analyses. One of ground motions is recorded in near fault; the other is recorded in far fault. Also, the two records have the same peak ground acceleration. The study mainly consists of three parts to assess the effects of reservoir length on the seismic performance of the concrete gravity dam. In the first part, the linear time-history analyses of the four finite element models prepared for the Folsom gravity dam are performed. In the second part, the seismic performance of the dam is evaluated according to demand–capacity ratio and cumulative inelastic duration. Finally, the nonlinear time-history analyses of the finite element models of the dam are carried out by using Drucker–Prager yield criteria for dam concrete. It is seen from the analyses results that the seismic behavior of the concrete gravity dams is considerably affected from the length of the reservoir. The reservoir length of 3H is adequate for concrete gravity dams. The selection of ground motion is on of the important parts of seismic evaluation of gravity dams. Also, the frequency characteristics of the ground motion having the same peak ground acceleration affect the seismic performance of the dam. The near-fault ground motions are generally creates more stress on the dam body than far-fault ground motions. The used performance approach provides a systematic methodology for assessment of the seismic performance and necessity of nonlinear analyses for dam systems.     

黄土坡滑坡的离散元研究

根据黄土坡滑坡所处的深部地质和表层古滑坡体结构特征，建立滑坡地质环境模型，运用离散元数值模拟方法研究黄土坡滑坡与深部地质环境的关系，明确了其形成机理，认为软硬相间的岸坡地层及顺向坡特点构成了黄土坡滑坡形成的形成的物质条件和发生背景环境，其内在力学机制是深部软硬相间岩层在重力蠕滑作用下发生的拱张，在考虑不同荷载组合的情况下预测评价滑坡的稳定性变化，滑坡体上建筑荷载会抑制中部剪切滑移区的发展，但能使滑坡体前端剪切滑移区扩大，从而降低滑体前缘的稳定性。     

A Bonded Particle Model Simulation of Shear Strength and Asperity Degradation for Rough Rock Fractures

Different failure modes during fracture shearing have been introduced including normal dilation or sliding, asperity cut-off and degradation. Attempts have been made to study these mechanisms using analytical, experimental and numerical methods. However, the majority of the existing models simplify the problem, which leads to unrealistic results. With this in mind, the aim of this paper is to simulate the mechanical behaviour of synthetic and rock fracture profiles during direct shear tests by using the two-dimensional particle flow computer code PFC2D. Correlations between the simulated peak shear strength and the fracture roughness parameter D _R1 recently proposed by Rasouli and Harrison (2010) are developed. Shear test simulations are carried out with PFC2D and the effects of the geometrical features as well as the model micro-properties on the fracture shear behaviour are studied. The shear strength and asperity degradation processes of synthetic profiles including triangular, sinusoidal and randomly generated profiles are analysed. Different failure modes including asperity sliding, cut-off, and asperity degradation are explicitly observed and compared with the available models. The D _R1 parameter is applied to the analysis of synthetic and rock fracture profiles. Accordingly, correlations are developed between D _R1 and the peak shear strength obtained from simulations and by using analytical solutions. The results are shown to be in good agreement with the basic understanding of rock fracture shear behaviour and asperity contact degradation.     

复杂地质条件下多结构面对重力坝坝基稳定性的影响及处理

武都重力坝坝基地质条件复杂,发育有断层、层间错动带等多种不利地质构造,且结构面相互交错组合形成多条潜在滑移面,坝基深层抗滑稳定问题突出。为了研究多结构面对坝基深层抗滑稳定的影响及加固处理,结合武都重力坝19#坝段,建立了三维数值模型进行有限元分析。首先,对坝基中各软弱结构面的力学参数进行敏感性分析,研究影响坝基稳定的主要因素,揭示了坝踵处倾向下游的10f2、F31断层对坝基抗滑稳定影响较大,应进行重点加固处理。在该基础上,在断层10f2、F31拟定不同深度的混凝土置换,对断层置换混凝土的深度进行敏感性分析,得出不同置换深度下坝基的超载稳定安全系数。结果表明,断层10f2、F31的置换深约19 m时可以达到良好的加固效果,位移和应力值得到良好的改善,坝基塑性区域明显减小,抗滑稳定安全系数得到明显提高,并满足设计规范要求。研究成果对武都重力坝工程的加固处理提供了重要的科学依据,对类似工程的稳定分析与加固处理具有参考价值。     

混凝土重力坝双滑面抗力方向角的取值研究

在《混凝土重力坝设计规范》(SL319-2005)中标准双滑面的稳定性程度推荐采用等K法进行计算,但对于抗力方向角的选取并没有统一的标准,研究表明,该方法中抗力角的选取对计算结果比较敏感。为了得到合理的抗力方向角,采用Sarma法、有限元法及刚体极限平衡法中的无条分法对抗力角的选取进行了深入的探讨,并给出了抗力方向角的选取建议。最后通过具体混凝土重力坝工程实例,依据抗力角的选取建议对其沿缓倾角软弱结构面的抗滑稳定问题进行分析,并给出了其最危险滑移面。     

A rigorous solution for the stability of polyhedral rock blocks

Block theory has been widely applied to stability analysis of rock engineering due to its clear concept and elegant geometrical theory. For a general block with multiple discontinuity planes, it is assumed that contact is only maintained on a single plane (single-plane sliding) or two intersecting planes (double-plane sliding) in block theory analysis. Since the normal forces and shear resistances acting on the other discontinuity planes are omitted, it can cause unreasonable estimations of block failure modes and incorrect calculation of factors of safety. In this study, a new method is presented that permits to consider the contribution of the normal forces and shear resistances acting on each discontinuity plane to the block stability. The proposed method meets all of the force-equilibrium and moment-equilibrium conditions and provides a rigorous solution for stability of general blocks with any number of faces and any shape. Some typical polyhedral blocks in rock slopes are analyzed using block theory and the proposed method. The results indicate that the traditional block theory may give a misleading conclusion for the predictions of stability and sliding direction of rock blocks when contact occurs on more than two discontinuity planes.     

强度折减DDA方法及其在稳定分析中的应用

在自行研制的非连续变形分析（discontinuous deformation analysis,DDA）程序中实现了自动强度折减法以模拟边坡的稳定性和安全系数。通过锦屏高边坡和某重力坝深层滑动的计算分析以及与刚体极限平衡法和有限元方法的比较研究可以看出,强度折减DDA法可以较高精度求出岩石高边坡的安全系数,但求得的重力坝深层抗滑稳定安全系数要低于刚体极限平衡法的结果。基于强度折减技术的DDA与FEM的耦合方法,可以较准确地求出重力坝深层抗滑稳定安全系数。     

基于岩体抗压强度折减的边坡稳定性分析方法

在岩体边坡稳定性分析方法中,基于非线性Hoek-Brown准则的强度折减法,存在折减方案不统一或计算太复杂等问题。针对这一问题,提出了一种基于岩体抗压强度的广义Hoek-Brown准则强度折减法,比直接折减材料参数,更能体现强度衰减的物理意义。方案以岩体单轴抗压强度作为折减依据,对岩石单轴抗压强度s_ci和反映岩体结构特征的参数组合s^a（s、a 均为模型参数）进行同比折减,分析该方案下抗剪切强度和抗拉强度的折减比例,并基于平均抗剪强度定义安全系数。应用该方案,对两个经典边坡算例进行稳定性分析,将所得安全系数、临界滑动面与局部线性化强度折减法、极限平衡法进行对比。结果表明,对于两算例,本方法所得安全系数与其他两种方法结果接近,相对误差低于2%;在算例1中,本方法得到的临界滑动面位置与其他两种方法结果一致性很高;在算例2中,本方案滑动面位置更接近于局部线性化法,且能同时反映剪切和拉伸破坏。以上结果验证了本强度折减方案和安全系数定义法的可靠性和合理性。