Dynamic analysis and numerical modeling of the 2015 catastrophic landslide of the construction waste landfill at Guangming,Shenzhen, China

Since lots of underground and slope excavation works were conducted during the urbanization process, an increasing number of sites in ravines around a city have been used to stockpile a large amount of excavated soils. This brings a huge challenge for researchers and managers in the risk evaluation and mitigation of potential dangers of these man-made construction waste landfills. This paper describes a recently large landslide of the construction waste landfill, which occurred at a site of Guangming new district in Shenzhen, China, on December 20, 2015. This catastrophic landslide caused the death of 69 persons and 8 persons are still missing. In this paper, this landslide was numerically simulated and analyzed. In spite of neither high-intensity rainfall nor antecedent rainfall, a slope of this landfill with a relative height of 111 m sided and caused about 2.34 million cubic meters of the soils to travel over a gentle terrain more than 1.2 km. This means that the landslide mobility index (H/L = 0.092) is much lower than a general designed value and the values in most other cases. A depth-integrated continuum method and a MacCormack-TVD finite difference algorithm are adopted, in this paper, to numerically simulate the dynamic process of this large landslide. It is found that a Coulomb friction model with consideration of the pore water pressure effects can well reproduce the main characteristics of the dynamic process of this landslide. Sensitivity analysis has demonstrated that the high pore water pressure in the soils plays a significant role in its mobility and is a key factor to the severity of this landslide.     

Shear strength of municipal solid waste for stability analyses

This paper investigates the shear strength of municipal solid waste (MSW) using the back analysis of failed waste slopes as well as field and laboratory test results. Shear strength of MSW is a function of many factors such as waste type, composition, compaction, daily cover, moisture conditions, age, decomposition, overburden pressure, etc. These factors together with non-standardized sampling methods, insufficient sample size to be representative of in situ conditions, and limited shear displacement or axial strain imposed during the laboratory shear testing have created considerable scatter in reported results. Based on the data presented herein, large shear displacements are required to mobilize the peak shear strength of MSW which can lead to displacement incompatibility between MSW and the underlying material(s) such as geosynthetic interfaces and foundation soils. The data presented herein are used to develop displacement compatible shear strength parameters for MSW. Recommendations are presented for modeling the displacement and stress dependent strength envelope in stability analyses.     

粗粒料强度准则与排土场稳定性研究

排土场稳定性主要取决于排土场的坡角及排弃废石的内部强度。通过低压到高压的三轴压缩试验研究了千枚岩粗颗粒散体材料强度的特性及压力对其强度的影响。试验表明：粗颗粒材料的破碎率随着压力的增大而增加,而增加速率则随着压力的增大而减小,并给出了一个用于描述压力及破碎率的关系式。提出了考虑破碎对强度影响的强度准则,该准则能描述粗颗粒材料的强度随压力的变化情况。采用该强度准则分析排土场的稳定性,其结果更加接近实际情况。而采用摩尔-库仑强度准则计算得到的排土场稳定性安全系数偏大,存在安全隐患。建议采用本文提出的强度准则分析排土场稳定性,特别是对于超高排土场的稳定性分析,更加适用该强度准则。     

Application of geogrids in waste dump stability: a numerical modeling approach

Geosynthetic is widely used to reinforce the weak rock mass, mine waste dump, soil slopes road cut slopes, etc. The present paper discusses the effect of geogrids on the stability of mine waste dump. The stability of mine waste dump has been done by Fast Langrage Analysis of Continua (FLAC) slope software, which is based on finite difference method. Reinforcement by geogrids mainly depends on the tensile strength, aperture size of geogrids, and particle size distribution of dump rock mass. Different permutations and combinations of spacing between two geogrid sheets have been taken into consideration to study the stability of mine waste dump. The factor of safety is calculated to quantify the effect of geogrids on waste dump slope. It has been observed from numerical modeling that the maximum slope angle is 45° at a height of 10 m. The scope of increasing slope angle from 45 to 60° is evaluated using geogrids. It has been found from the study that the factor of safety increases as the spacing between geogrids decreases. Maximum strain is also plotted of each case to identify the slip circle. The positions of geogrids modify the probable slip circle or failure plane of mine waste dump. Using ten geogrids at a spacing of 1 m, the slope angle can be increased up to 60° with factor of safety of 1.4.     

滑(边)坡稳定性计算分析中的滑坡推力计算方法

滑坡推力计算一直是边坡稳定性分析、防护加固设计及滑坡治理抗滑工程设计中的核心问题。根据抗滑支挡工程结构与被加固滑坡体的力学关系,滑坡推力计算方法可概括为分离法、虚力法及结构与岩土数值耦合法。不同的计算方法得到的滑坡推力值有差异。用以上3种方法对拟设桩结构物的内力进行计算,对比分析发现,分离法及虚力法最终均需对桩侧滑坡推力分布形式进行假定,假定分布形式不同所得内力不同;数值耦合法可直接得到桩侧应力分布形式,且考虑了桩与岩土的偶合效应,计算结果较为合理,有必要进一步分析研究与推广应用。     

排土场土石混合体分形特征与抗剪强度特性研究

露天矿山剥离堆积的土石混合体颗粒尺度不一,且力学性质异常复杂。以西藏甲玛铜矿南坑排土场为研究对象,采用现场勘测的方法测定堆积体的粒度组成及其分布特征,开展室内重塑土样的固结排水三轴压缩试验,以分析土体屈服强度特性与剪胀性,以及抗剪强度参数的取值。研究结果表明,自排土台阶坡顶至坡底,土石混合体的土粒减少且块石增多,颗粒的平均粒径呈指数关系增大;土体的粒度分布具有显著的分形结构特征,随块石含量的增大,其粒度分形维数减小。块石含量不同的土样在偏差应力作用下均表征出压密、屈服、塑性流动破坏的剪切特性,且围压条件与块石含量是影响土体剪切变形的两个关键因素,低围压时增加块石含量,土体更易产生剪胀。摩尔库伦强度准则能客观反映土体屈服的现象及过程,随块石含量的增加,土体的黏聚力呈线性减小且内摩擦角呈指数增大。     

重庆韦家沟矸石山滑坡成因分析

对韦家沟老矸石山进行勘察、研究,分析了矸石山的滑坡成因机制,揭示出特殊堆积散体构成、排弃地点条件、排弃强度等因素造成矸石山特殊堆积特征,导致矸石山具有二元空间结构、堆积地点水文地质条件改变、可能失稳滑动方式形成及呈现自组织临界性等性状,进而影响着矸石山稳定性的变化发展。在此基础上,采用极限分析上限法及数值模拟分析评价矸石山的稳定性,最后根据分析结果,提出相应的矸石山滑坡灾害防治措施。文章将定性分析与定量计算相结合,研究方法及结论可为类似矸石山地质灾害防治提供参考。     

Effects of monsoonal rainfall on waste dump stability and respective geo-environmental issues: a case study

The stability of mine waste dumps is of critical importance and an issue, the mining industry of Goa, India is continually facing. The State of Goa receives high rainfall of around 3,000 mm annually. This heavy monsoonal rainfall is often believed to be the cause of dump slope instability. In light of several dump collapses encountered in the State and their damaging effects on both mine operations and local geo-environmental conditions, this paper examines their stability considering various geotechnical factors and the downstream environmental effects of a slope failure. The mechanical properties of dump waste material are reported at different compaction levels. The effect of these properties and changes in pore-water pressure are specifically examined using limit equilibrium analysis. An empirical formula is developed relating dump height, material mechanical parameters and pore-water pressure to the factor of safety of the slope. It was found that the level of compaction experienced by the material had a significant effect on the factor of safety.     

文家坝大型单体滑坡地质特征遥感调查与稳定性分析

平武县的文家坝滑坡是由汶川地震诱发,并曾阻断河流形成文家坝堰塞湖,威胁到下游南坝、锰矿厂和公路的安全,所以有必要对其地质特征进行调查及稳定性分析。通过对震后平武县SPOT卫星影像的解译,识别出了文家坝滑坡的地貌要素及滑坡物质组成,表面植被发育度,水文条件等地质特征。可以认为,文家坝滑坡为大型牵引式滑坡,目前仍处于不稳定状态,在余震、强降雨等条件下,有复滑的可能,并针对潜在威胁给出了具体的防治建议。     

滑坡稳定性计算和滑坡稳定性量化评分方法的适用性对比研究——以湖南衡东某风电场公路切坡为例

拟以湖南衡东某风电场公路切坡为例,对比分析了公路切坡稳定性评价常用的两种分析方法,即滑坡稳定性计算和滑坡稳定性量化评分,以具体的工程项目为案例,依据公路切坡引发滑坡的地质环境条件,应用两种方法对该切坡可能形成的滑坡进行了对比分析。研究表明:对于勘查程度较高的大型滑坡稳定性评价,采用滑坡稳定性定量计算方法,结论较为准确;对于勘查程度较低的中小型滑坡稳定性评价,采用滑坡稳定性量化评分法,可减少工作量,结论较为准确;对于为大型且地质环境条件复杂,建议用两种方法相互论证,结论可信度高。     

Forensic analysis and numerical simulation of a catastrophic landslide of dissolved and fractured rock slope subject to underground mining

Landslides - Based on field geological survey and unmanned aerial vehicle (UAV) photography, this paper studied the inherent causes, intrinsic mechanisms, and kinematic characteristics of a...     

高寒矿区软弱基底排土场边坡稳定性数值模拟

为研究青藏高原东北部高寒地区冻融条件下,软弱基底露天煤矿排土场边坡变形破坏模式和边坡极限堆载高度,本文以青海天峻祁连山北缘江仓露天煤矿排土场作为试验区,采用二维有限元法模拟分析了5种不同堆载高度工况下排土场边坡变形破坏模式,基于折减系数法确定排土场边坡安全系数和稳定性评价。分析结果表明:在容许堆载高度范围内,随着排土场边坡堆载高度的增加,排土场边坡位移量表现出显著增长的变化趋势,其水平方向与垂直方向最大位移量分别为1. 631 m和6. 320 m,当超过容许堆载高度范围,排土场边坡位移量发生突变,呈显著性降低的变化趋势,其位移量降低幅度为64. 27%～102. 32%;塑性变形区表现出沿排土场边坡承载基底位置处的草甸型软弱界面,向排土场边坡坡底位置扩展;剪应力在坡底位置处出现应力集中现象,且剪应力集中范围由边坡承载基底向上、向坡体内部扩展且呈连通趋势,其结果形成后缘拉裂、前缘剪切滑移的整体边坡变形破坏模式;排土场边坡安全系数随着堆载高度的增加表现出二次函数降低(R~2=0. 9896)的变化规律,当排土场边坡高度为65 m时,则达到边坡设计容许高度,且其安全系数为1. 25。本次研究所得到的排土场承载由草甸构成的软弱基底在坡底位置处的变形结果,与野外试验区边坡堆载作用下所形成的实际情况基本吻合。研究结果可为高寒矿区排土场边坡变形破坏科学防治,提高边坡稳定性研究,提供理论支撑依据和实际指导意义。     

Effects of anisotropy in correlation structure on the stability of an undrained clay slope

Slopes are mainly naturally occurred deposits, so slope stability is highly affected by inherent uncertainty. In this paper, the influence of heterogeneity of undrained shear strength on the performance of a clay slope is investigated. A numerical procedure for a probabilistic slope stability analysis based on a Monte Carlo simulation that considers the spatial variability of the soil properties is presented to assess the influence of randomly distributed undrained shear strength and to compute reliability as a function of safety factor. In the proposed method, commercially available finite difference numerical code FLAC 5.0 is merged with random field theory. The results obtained in this study are useful to understand the effect of undrained shear strength variations in slope stability analysis under different slope conditions and material properties. Coefficient of variation and heterogeneity anisotropy of undrained shear strength were proven to have significant effect on the reliability of safety factor calculations. However, it is shown that anisotropy of the heterogeneity has a dual effect on reliability index depending on the level of safety factor adopted.     

Three-dimensional undrained tunnel face stability in clay with a linearly increasing shear strength with depth

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.     

高陡边坡滑坡体黄土的强度特性研究

黄土台塬是黄土地区典型的地貌特征,塬边多为高陡边坡,极易发生崩塌和滑坡地质灾害。位于陕西境内泾河以南的黄土塬－泾阳南塬为典型的高陡黄土边坡,其崩塌、滑坡地质灾害频繁发生,自东南向西北的大小滑坡形成了延绵约30 km的滑坡群。对泾阳南塬滑坡群进行分析,以其中一规模较大的近年滑坡--东风滑坡为例进行了实地考察、现场测量,对滑坡体后缘和前缘的黄土进行了一系列的室内物理和力学性质试验。分析了高陡黄土边坡滑坡的发生过程和破坏机制,由颗粒分析和湿陷性试验得出滑坡体前后缘土体的湿陷液化特征。分析了不同含水率对强度参数的影响,并对比分析了原状黄土和重塑黄土的强度参数和结构性,验证了重塑饱和黄土的应力-应变关系和体应变-轴应变关系与邓肯-张模型符合较好,为高陡黄土边坡稳定性分析强度参数的合理选取提供了参考     

Failure of a mine waste dump in Zimbabwe: Causes and consequences

A combination of factors are considered important in causing the failure and subsequent development of a flowslide of a gold mine waste dump (or tailings dam) at Arcturus, near Harare, Zimbabwe. These factors comprise poor basal drainage, steep perimeter walls, saturation of the walls and basal sediments through continued spigoting of slurry during a period of heavy rainfall, and the effect of this saturation on the tailings. Properties of the tailings, eyewitness accounts, documentary evidence, and site characteristics are discussed. The failure and subsequent development of a fatal 300-m flowslide are reconstructed in a five-phase developmental model. The general applicability of the results is discussed.     

Comprehensive analyses of the initiation and entrainment processes of the 2000 Yigong catastrophic landslide in Tibet,China

The 2000 Yigong landslide was one of the most catastrophic landslides worldwide, resulting in huge casualties and property losses. The dynamic process of the Yigong landslide was very complicated, especially for the initiation and entrainment mechanism during the landslide movement process. The topography, geological condition, traces left by the landslide, and distribution characteristics of the landslide deposits were determined by field investigations, combined with several years of monitoring the temperature and rainfall data in this region. The initiation mechanism of the Yigong landslide is presented. The main reasons for the landslide initiation are as follows: the strength reduction of rock masses (especially for the weak structural surface), the impact from years of freeze-thaw cycles, the superposition of glacier melting and heavy rainfall on the slope, and a slope that was almost at the limit state before the landslide. Laboratory tests and physical modeling experiments were carried out to study the entrainment process of this landslide. Combined with the topographic survey data and theoretical analyses, the entrainment mechanism during the movement process of the Yigong landslide is presented. The old landslide deposits on the lower slope collided with and were scraped by the high-speed debris avalanche, which resulted in the volume amplification of the landslide. The existence of water plays a key role during the landslide initiation and movement processes.     

复杂边坡稳定性的二维与三维分析

目前,在边坡稳定性分析中广泛地采用二维极限平衡分析方法进行研究。但是对于地形、地层、地下水、岩体结构等条件复杂的边坡,仅用二维极限平衡分析方法进行研究是不够的,二维分析忽略了边坡的三维效应,而复杂边坡往往受三维效应影响大。但至今三维极限平衡方法还不是很完善。因此,本文结合一工程实例,采用二维与三维极限平衡分析相结合的方法对其边坡的稳定性进行了分析。研究结果表明,对于复杂边坡,应用二维和三维稳定性分析相结合的方法进行研究是一种较为恰当的选择。     

Continuum deformation and stability analyses of a steep hillside slope under rainfall infiltration

Rainfall weakens an earth slope in a number of ways. It increases the degree of saturation of the soil, thereby breaking the bonds created by surface tension between the soil particles. When the volume of infiltrating water is large enough to mobilize fluid flow inside the soil matrix, the fluid exerts a downhill frictional drag on the slope, creating a destabilizing effect. When excess fluid can no longer infiltrate the slope due to increased saturation in the soil, it is discharged as a surface runoff and erodes the slope. In this paper, we present a physics-based framework for continuum modeling of a hydrologically driven slope failure similar to what occurred in a steep experimental catchment CB1 near Coos Bay, Oregon. We quantify the rainfall-induced slope deformation and assess the failure potential of the slope using finite element modeling that couples solid deformation with fluid pressure in an unsaturated soil. Results of the studies suggest that for a steep hillside slope underlain by a shallow bedrock similar to the CB1 site, failure would occur by multiple slide blocks with the failure surfaces emerging on the slope face. These results suggest that an infinite slope mechanism would be insufficient to represent the failure kinematics for a slope similar to CB1.     

Lateral strength and critical depth in infinite slope stability analysis

Infinite slope (IS) method is the simplest limit equilibrium method for slope stability analysis. It gives reliable results for slides where the longitudinal dimension prevails on the depth of the landslide. Usually results are conservative since ignoring the effects of the strength along lateral bounds. Here, starting from the assumption of considering the effects of the shear strength along lateral bounds by a rectangular cross section, a new expression of the safety factor is investigated, based first on an elliptical and then on a parabolic cross section of the landslide mass. The safety factor evaluated in this way can be quite different from those returned by the classic formula of IS model, in particular when the width of the landslide is narrow with respect to its depth and the ratio between the width and the depth of the landslide is lower than 5. An interesting implication of the proposed model is that if cohesion differs from zero, there is a ‘critical depth’, where the safety factor has a minimum value. Copyright © 2013 John Wiley & Sons, Ltd.