Stability analysis of intermittently jointed rock slopes based on the stepped failure mode

In practical engineering,due to the noncontinuity characteristics of joints in rock slopes,in addition to plane failure,stepped sliding failure may occur for intermittently jointed rock slopes.Especially for intermittently bedding jointed rock slopes,the correlation and difference in strength parameters between joints and rock bridges,along with the various failure modes and intermittency of rock bridges,contribute to the complexity of stepped failure modes and the unpredictability of failure regions.Based on the upper-bound limit analysis method and multi-sliders step-path failure mode,considering the shear and tensile failure of rock bridges and the weakened relationship between the strength parameters of rock bridges and jointed surfaces,by introducing the modified M-C failure criterion and the formula for calculating the energy consumption of tensile failure of rock bridges,two failure mechanisms are constructed to obtain the safety factor(F_(s))of intermittently jointed rock slopes.The sequential quadratic programming method is used to obtain the optimal upper-bound solution for F_(s).The influence of multiple key parameters(slope height H,horizontal distance L,Slope angleβ,shear strength parameters of the rock bridgeφr and cr,Dimensionless parameter u,weakening coefficients of the internal friction angle and cohesion between the rock bridges and joint surfaces Kφand Kc)on the stability analysis of intermittently jointed rock slopes under the shear failure mode of rock bridges as well as under the tensile failure mode is also explored.The reliability of the failure mechanisms is verified by comparative analysis with theoretical results,numerical results,and landslide cases,and the variation rules of F_(s)with each key parameter are obtained.The results show that F_(s) varies linearly withφr and cr of the rock bridge and with K_(φ)and K_(c),whereas F_(s)changes nonlinearly with H and L.In particular,with the increase in Kφand Kc,Fs increases by approximately 52.78%and 171.02%on average,respectively.For rock bridge tensile failure,F_(s) shows a nonlinearly positive correlation withφr,cr,Kφand Kc.In particular,with the increase in Kφand Kc,Fs increases by approximately 13%and 61.69%on average,respectively.Fs decreases rapidly with increasing slope gradientβand decreasing dimensionless parameterμ.When Kφand Kc are both less than 1.0,the stepped sliding surface occurs more easily than the plane failure surface,especially in the case of tensile failure of the rock bridge.In addition,rock slopes with higher strength parameters,taller heights,and greater weakening coefficients are prone to rock bridge tension failure with lower Fs,and more attention should be given to the occurrence of such accidents in actual engineering.

Seismic stability of jointed rock slopes under obliquely incident earthquake waves

Seismic stability of slopes has been traditionally analyzed with vertically propagated earthquake waves.However,for rock slopes,the earthquake waves might approach the outcrop still with a evidently oblique direction.To investigate the impact of obliquely incident earthquake excitations,the input method for SV and P waves with arbitrary incident angles is conducted,respectively,by adopting the equivalent nodal force method together with a viscous-spring boundary.Then,the input method is introduced within the framework of ABAQUS software and verified by a numerical example.Both SV and P waves input are considered herein for a 2 D jointed rock slope.For the jointed rock mass,the jointed material model in ABAQUS software is employed to simulate its behavior as a continuum.Results of the study show that the earthquake incident angles have significance on the seismic stability of jointed rock slopes.The larger the incident angle,the greater the risk of slope instability.Furthermore,the stability of the jointed rock slopes also is affected by wave types of earthquakes heavily.P waves induce weaker responses and SV waves are shown to be more critical.

Numerical investigations of rock bridge effect on open pit slope stability

In this study,the effect of rock bridges on rock slope stability was investigated by incorporating nonpersistent joint networks in numerical models,and the critical profiles of an open pit mine were analysed.Parallel deterministic networks of infinite and finite lengths,ubiquitous joint network model and Veneziano joint network model were used in order to simulate the rock fractures.Materials were modelled based on the generalised Hoek-Brown and equivalent Mohr-Coulomb failure criteria.The parallel deterministic infinite and the ubiquitous joint network models produced lower safety factors.The introduction of rock bridges along discontinuity planes in the parallel deterministic network and Veneziano joint network models significantly contributed to the stability and strain distribution,which should be considered in stability analysis of rock mass in open pit by rock slope practitioners.The results show the significance of joints in hard rock behaviour and the joints should be included in order to attain practical and realistic simulations.

Test analysis of stress characteristics on reinforcing rock slope with group anchorage cable

To research the reinforcement effect of a rock slope with group anchorage cablesand the stress characteristics of pre-stressed anchorage cables in the fractured surface,the rock slope calculated model of a wedge block within the double-slide face wasestablished by using the finite difference software according to the actual slope projectcombined with indoor model test.The pre-stress loss rule of the anchorage cable andthe distribution of axial force and the force-transferring mechanism of the anchorage cablewere analyzed during simulation.Also, based on the displacement contour and thesafety factor of the calculated results, the quantitative analysis for the reinforcement effectof the rock slope with group pre-stressed anchorage cable was discovered.The resultscomputed by the software conform with the data in the experiment, which canprove the effectiveness and correctness of parameter selection and model building.

Influence of rock property correlation on reliability analysis of rock slope stability: From property characterization to reliability analysis

Cohesion(c) and friction angle(φ) of rock are important parameters required for reliability analysis of rock slope stability. There is correlation between c and φ which affects results of reliability analysis of rock slope stability. However, the characterization of joint probability distribution of c and φ through which their correlation can be estimated requires a large amount of rock property data, which are often not available for most rock engineering projects. As a result, the correlation between c and φ is often ignored or simply assumed during reliability studies, which may lead to bias estimation of failure probability. In probabilistic rock slope stability analysis, the influence of ignoring or simply assuming the correlation of the rock strength parameters(i.e., c and φ) on the reliability of rock slopes has not been fully investigated. In this study, a Bayesian approach is developed to characterize the correlation between c and φ, and an expanded reliability-based design(RBD) approach is developed to assess the influence of correlation between c and φ on reliability of a rock slope. The Bayesian approach characterizes the sitespecific joint probability distribution of c and φ, and quantifies the correlation between c and φ using available limited data pairs of c and φ from a rock project. The expanded RBD approach uses the joint probability distribution of c and φ obtained through the Bayesian approach as inputs, to determine the reliability of a rock slope. The approach gives insight into the propagation of the correlation between c and φ through their joint probability into the reliability analysis, and their influence on the calculated reliability of the rock slope. The approaches may be applied in practice with little additional effort from a conventional analysis. The proposed approaches are illustrated using real c and φ data pairs obtained from laboratory tests of fractured rock at Forsmark, Sweden.

含雁列式断续节理的岩质边坡失稳机制模拟研究

岩质边坡的阶梯状破坏是一种常见的失稳破坏类型,其稳定性主要受岩质边坡内部的不连续结构面和岩桥控制。为了探究雁列式裂纹间相对位置的复杂变化对节理岩质边坡阶梯状破裂面形成的影响,基于零厚度黏聚力(Cohesive)单元,采用重力增加法开展了考虑裂隙倾角、岩桥倾角、岩桥长度的含雁列式裂纹岩质边坡阶梯状破坏数值模拟。通过对于模拟结果的编程处理,实现了节理岩质边坡破坏过程中的声发射模拟,结合岩质边坡破坏过程的应力、位移云图,进一步分析了节理岩质边坡阶梯状破裂面形成的演化过程与力学机制。研究表明:节理岩质边坡模型的破坏模式可分为持续破坏型和渐进破坏型,渐进破坏模式的出现主要与裂纹倾角和岩桥倾角有关;岩质边坡阶梯状滑裂面的形成是一个岩桥从下至上逐渐贯通的过程,其破坏过程分为等速变形阶段和加速变形阶段;随着裂纹倾角的增加,岩质边坡的岩桥贯通所需要的荷载逐渐增加;随着岩桥长度的增加,岩质边坡内部岩桥破裂贯通所产生的声发射事件数和裂纹扩展总长度逐渐减小;相比于裂纹倾角和岩桥长度,岩桥倾角对于节理岩质边坡中岩桥贯通与阶梯状破裂面形成的影响较小。本文研究了多种工况下含雁列式断续节理岩质边坡的失稳机制,以期为该类型岩质边坡的稳定性评价与失稳防控提供一定的理论参考。

节理倾角对岩质边坡稳定性影响的数值模拟研究

在露天矿山岩质边坡中往往存在大量的节理裂隙,节理倾角对岩质边坡稳定性的影响研究对于露天矿山灾害防护至关重要。论文利用FLAC 3D分析了节理倾角对含单节理岩质边坡的稳定性的影响以及对动力波在岩质边坡中传递的影响。研究发现,单节理岩体的单轴抗压强度和弹性模量随节理倾角增大呈“U”形分布。含单节理岩质边坡的安全系数随节理倾角增大近似呈“U”形分布。

岩石结构面Grasselli二维粗糙度指标优化及其JRC估算

采用只考虑迎剪侧表观倾角而忽略内部起伏角的Grasselli二维形貌参数θ_(G)来估算结构面粗糙度系数JRC仍有待改进。从θ_(G)的物理意义出发,发现爬坡区内部凸起高度对粗糙度的贡献可表示为其在总爬坡水平距离上的坡角,所有爬坡区提供的坡角之和定义为结构面内部起伏体粗糙贡献,将结构面迎剪侧表观平均倾角θ_(G)和爬坡区内部平均坡角θ_(H)叠加,提出岩石结构面粗糙度新指标θ_(C)。通过获取十条标准JRC剖面线的θ_(C),分析其与JRC之间的关系,建立基于θ_(C)的JRC估算式。计算不同采样间距和不同采样方向下的新指标θ_(C),结果显示θ_(C)具有分形特征且能够反映结构面形貌各向异性。进一步将JRC估算式应用于JRC-JCS模型,通过对比已有研究得到的试验结果以及不同抗剪强度模型的预测效果,验证基于新指标θ_(C)估算的JRC可以准确预测结构面峰值抗剪强度。最后,对二维指标θ_(C)进行三维拓展,提出三维粗糙度新指标(θ_(C))_(3D),并通过结构面形貌各向异性表征验证了其合理性。

轻质混凝土在破碎岩质边坡支护中的应用与性能分析

目前已有多种边坡支护技术来确保坡体的稳定性,但实际施工中依旧存在工序复杂繁琐、施工现场技术要求高、施工周期长等诸多问题。轻质混凝土的轻质特性使其近年来开始被逐渐应用到边坡防护中。对轻质混凝土特性进行了概述,分析了其在破碎岩质边坡支护中的应用优势与发展前景。重点设计了边坡支护工程中装配式组合护坡节点结构,优化了轻质混凝土各原材料配合比,使用ABAQUS模拟并分析构件的受力情况和应力分布情况。通过加载试验分析了轻质混凝土构件的结构承载力、变形性能,结果表明:轻质混凝土构件在整体加载过程中裂缝产生较少,有着较好的延性,在500 kN荷载下,最大裂缝约0.7 mm。

顺向节理高陡岩质边坡破坏机理研究

为了研究顺向节理高陡岩质边坡破坏机理,指导邻近高铁的顺向节理高陡岩质边坡工程项目安全生产,采用离散元数值模拟计算的方法,对均质无节理、切层节理、隐伏节理高陡岩质边坡进行稳定性计算,研究了坡面倾角、切层节理倾角和隐伏节理间距对边坡稳定性的影响规律,研究表明,当切层节理倾角小于10°时,破坏形式为圆弧滑动破坏;当切层节理倾角大于20°时,破坏形式为阶梯型滑动破坏;当切层节理倾角大于30°时,破坏形式为单层面滑动破坏;隐伏节理边坡易发生溃曲破坏,且随着节理间距的增加,边坡安全系数先逐渐增大,而后趋于稳定。研究结果表明,针对含切层节理和隐伏节理边坡,其破坏模式是双平面破坏,边坡的破坏经过了一个自下而上沿切层节理塑性破坏和一个自上而下沿隐伏节理拉伸破坏的过程,属于滑移-拉裂破坏。

基于离散元平节理模型的露天矿边坡局部破坏模式研究

离散元颗粒流方法中的平节理模型将颗粒曲面接触变为平线接触,克服平行黏结模型破坏时颗粒过度旋转.依托露采矿边坡工程,建立基于平节理模型的岩石单轴压缩模型和岩质边坡单台阶离散元数值模型.记录岩样模型的应力、应变和岩质边坡模型的形变、颗粒接触关系等指标与室内单轴压缩试验结果和现场边坡破坏规律进行对照.结果表明:平节理模型能较好的模拟岩石的单轴压缩试验和岩质边坡破坏过程.

多措施组合支护技术在岩质边坡加固中的应用

以水厂铁矿北区上盘两处边坡加固工程为背景,分析了边坡失稳破坏的模式,根据边坡工程安全等级,参照规范合理选取了不同工况下边坡设计安全系数,根据边坡顺层节理发育情况,选取最不利滑面,建立计算模型,采用折线滑动传递系数法,分析计算了边坡整体稳定性及剩余下滑力,并根据最不利工况下的剩余下滑力,进行了多措施组合支护体系设计计算,并分析了后期边坡顶部水平及垂直位移的监测数据。结果表明多措施组合支护体系,在顺层节理发育的岩质边坡加固治理中,方案合理,效果显著,边坡加固完成后至今未出现任何安全隐患,边坡稳定性良好。

基于裂隙网络有限元的破碎岩体边坡变形破坏演化规律

针对节理裂隙在降雨入渗、人工活动等作用下持续劣化引发边坡变形破坏问题,以广西在建的天峨—巴马高速公路沿线某破碎岩体边坡为依托,采用裂隙单元和实体单元相结合的方式对破碎裂隙岩体进行建模,模拟了该边坡在节理裂隙持续劣化影响下的变形和破坏过程,分析了破碎岩体边坡的整体和局部变形、破坏的发展规律。

基于离散元法的节理岩体边坡稳定性分析

节理岩体边坡的稳定性在很大程度上取决于节理的强度及其分布形式。由于节理岩体边坡的失稳破坏具有大变形和非连续的特点,因此,离散单元法成为研究节理岩体边坡破坏机制的最有效方法之一。通过采用离散元软件PFC2D进行数值模拟,对完整岩石及节理的力学性能进行研究,并建立含密集节理的岩体边坡模型,讨论了节理连通率对边坡破坏形式的影响。结果表明,节理岩体边坡的失稳破坏是一个渐进的过程;在多组节理密集分布的岩体边坡中,连通率越大,其稳定性越差;随着连通率的减小,边坡的破坏形式由大范围的滑坡转变为局部崩塌的形式。

用有限元强度折减法进行节理岩质边坡稳定性分析

通过对节理岩质边坡非线性有限元模型进行强度折减,使边坡达到不稳定状态时,有限元静力计算将不收敛,此时的折减系数就是稳定安全系数,同时可得到边坡破坏时的滑动面以及破坏过程,而传统条分法无法获得节理岩质边坡的滑动面与稳定安全系数。该方法为节理岩质边坡稳定分析开辟了新的途径,通过算例表明了此法的可行性。

地震作用下节理岩质边坡稳定性影响因素研究

汶川地震灾害调查表明,在基岩山区地震滑塌主要发育在局部强度相对较大、节理较发育的厚层或块状岩体中。以岩石中含两组节理的岩质边坡为例,输入实际的地震记录,采用离散单元法进行数值模拟,分别探讨坡高、地震烈度、坡角及节理倾角组合对节理岩质边坡稳定性的影响。结果表明:地震作用下坡体中质点的加速度、速度具有高程放大效应;节理岩质边坡稳定性随着坡高、坡角和地震烈度的增加而降低;两组节理不同组合的岩质边坡,其稳定性变化较为复杂,受节理倾角与坡角的关系、节理的倾向、两组节理之间夹角等因素的影响。节理岩质边坡在地震作用下是受拉区逐渐向受剪区扩展而最终导致边坡失稳破坏,是受拉和受剪的复合破坏。上述初步结论为评价山区节理较发育的岩质边坡在地震作用下的稳定性提供一定的依据。

露天矿节理岩体边坡稳定性研究

针对眼前山露天矿南帮节理岩体边坡的结构特征,通过现场节理调查及统计分析,采用Monte-Carlo随机模拟方法,进行了节理三维网络的计算机模拟,研究确定了南帮边坡的节理岩体强度和破坏模式。通过滑动面自动搜索及FLAC数值模拟,系统地计算分析了南帮节理岩体边坡现执行开采和调整方案随采场逐渐下延的稳定状况,指出将三并段边坡的台阶坡面角由65°调整为60°可以从根本上改善眼前山露天矿南帮边坡的稳定状况,在矿山服务年限内满足开采的稳定性要求。

节理岩体边坡稳定性分析新方法

节理岩体边坡失稳破坏同时受控于节理与岩体抗剪强度。在对具有2组平行节理的岩体坡边失稳破坏机制研究基础上,研究了具有2组平行节理岩体边坡的极限平衡分析方法,并推导了相应的边坡稳定性分析计算公式,编制了基于潜在滑动面自动搜索的边坡稳定性研究程序。通过与文献中算例的对比研究,证明了所提出的节理岩体边坡稳定性分析方法的正确性,为具有2组平行节理岩体边坡的稳定性分析提供一条新的有效途径。

基于离散元的强度折减法分析岩质边坡稳定性

将通用离散元UDEC与强度折减法结合,对含多结构面的岩质边坡的稳定性进行了分析。通过对节理岩质边坡的UDEC模型中的可变形块体和节理单元的强度参数进行折减,使模型不能再达到平衡状态,此时的折减系数就是边坡的安全系数,另外,由对应的边坡块体的速度矢量可以确定滑动面和边坡的破坏形态。通过与传统的条分法的结果比较,表明基于UDEC的强度折减法是一种可靠、有效的方法,为复杂节理岩质边坡的滑动面确定与安全系数计算开辟了新的途径。

有限元强度折减法在土坡与岩坡中的应用

通过有限元强度折减,使边坡达到破坏状态时,滑动面上的位移将产生突变,产生很大的且无限制的塑性流动,有限元程序无法从有限元方程组中找到一个既能满足静力平衡又能满足应力-应变关系和强度准则的解,此时不管是从力的收敛标准,还是从位移的收敛标准来判断有限元计算都不收敛,因此采用力和位移的收敛标准作为边坡破坏的判据是合理的。对有限元强度折减法的计算精度和影响因素进行了详细分析,包括屈服准则、流动法则、有限元模型本身以及计算参数对安全系数计算精度的影响,并给出了提高计算精度的具体措施。研究表明:采用徐干成、郑颖人(1990年)提出的摩尔-库仑等面积圆屈服准则求得的稳定安全系数与传统Spencer法的误差在5%左右,证实了其实用于工程的可行性。在平面应变条件下则可采用摩尔匹配DP准则。该文还将此法应用于岩质边坡的稳定分析,得到了岩质边坡的滑动面和安全系数,开创了求节理岩质边坡滑动面与稳定安全系数的先例。