Three-dimensional stability of landslides based on local safety factor

Unlike the limit equilibrium method(LEM), with which only the global safety factor of the landslide can be calculated, a local safety factor(LSF) method is proposed to evaluate the stability of different sections of a landslide in this paper. Based on three-dimensional(3D) numerical simulation results, the local safety factor is defined as the ratio of the shear strength of the soil at an element on the slip zone to the shear stress parallel to the sliding direction at that element. The global safety factor of the landslide is defined as the weighted average of all local safety factors based on the area of the slip surface. Some example analyses show that the results computed by the LSF method agree well with those calculated by the General Limit Equilibrium(GLE) method in two-dimensional(2D) models and the distribution of the LSF in the 3D slip zone is consistent with that indicated by the observed deformation pattern of an actual landslide in China.

Landslide stability for Shuitianba in the Three Gorges area

According to the data of preliminary survey, the authors established a landslide geological model,on the basis of analyses on the sensitivity of landslide, tried to simulate and calculate the landslide stability of Shuitianba with the method of transfer coefficient when it is under different strength parameters, and study the landslide mechanism. The results show that it is sensitive to the effects of shear strength parameters of sliding zone and groundwater level on landslide stability safety coefficient, which provides reliable basis for calculation of landslide stability.

Engineering Geological and Geotechnical Studies of Taprang Landslide, West-central Nepal: An Approach for Slope Stability Analysis

Detailed investigation of Taprang landslide was carried out in order tounderstand the surface, subsurface lithological information and physicalproperties of soil by using multi-disciplinary methods such as engineeringgeological, geophysical and geotechnical studies for the determinationof factor of safety for slope stability analysis. Geological study wascarried out by detail mapping of surface geology, soil condition, propertiesof bedrock and its discontinuities. The geophysical survey (ElectricalResistivity Tomography-ERT) were carried out to know the electricalresistivity of soil for identifying the groundwater table and slip surface ofthe landslide. Geotechnical analysis such as grain size analysis, liquid limitand direct shear test were carried out in order to evaluate soil classification,moisture content, cohesion and the angle of internal friction of soil forknowing the strength the soil. These soil parameters indicate the soil is verylow strength. The combination of these results were used for calculatingthe factor of safety (FoS) by Limit Equilibrium Method (LEM) proposedby Bishop and Janbu methods. The result of factor of safety in the Tapranglandslide demonstrates that the slope become stable in drained (dry)condition, remain ultimate stage in undrained (wet) condition and finallyfailure occurs if applied the seismic load in both drained and undrainedconditions.

Stability assessment of landslide-prone road cut rock slopes in Himalayan terrain:A finite element method based approach

Large-scale slope destabilization could be aggravated due to swift urbanization and ever-rising demands of geoengineering projects such as dams,tunnels,bridges and widening roads.National Highway-58 connects Delhi to Badrinath in India,which passes through complex geomorphological and geological terrain and often encounters cut slopes susceptible to slope failures.In the present investigation,a detailed geotechnical appraisal is conducted along the road cut slopes from Rishikesh to Devprayag in the Himalayas.Twenty vulnerable road cut slopes were demarcated for detailed slope stability analysis using Phase2D finite element modeling simulator.Nonlinear generalized Hoek-Brown(GHB)criterion was adopted for stability analyses.Out of 20 slopes,five slopes(S6,S7,S18,S19 and S20)are unstable with factor of safety(FoS)less than or equal to 1,and thus needs immediate attention.The FoS values of four slopes(S2,S9,S13 and S17)lie between 1 and 1.3,i.e.marginally stable,and slopes S1,S3,S4,S5,S8,S10,Sll,S12,S14,S15 and S16 are stable.Mohr-Coulomb(MC)criterion was also adopted to compare the slope stability analysis with GHB criterion.The FoS calculated from GHB criterion is close to that using MC criterion for lower values of FoS whereas for higher values,the difference is marked.For the jointed rock in the Himalayan region,the nonlinear GHB criterion gives better results as compared to MC criterion and matches with the prevailing field conditions.Accordingly,some suggestions are proposed to strengthen the stability of cut slopes.

Optimal mining sequence for coal faces under a bedding slope:insight from landslide prevention

Repetitive mining beneath bedding slopes is identified as a critical factor in geomorphic disturbances, especially landslides and surface subsidence. Prior research has largely concentrated on surface deformation in plains due to multi-seam coal mining and the instability of natural bedding slopes, yet the cumulative impact of different mining sequences on bedding slopes has been less explored. This study combines drone surveys and geological data to construct a comprehensive three-dimensional model of bedding slopes. Utilizing FLAC3D and PFC2D models, derived from laboratory experiments, it simulates stress, deformation, and failure dynamics of slopes under various mining sequences. Incorporating fractal dimension analysis, the research evaluates the stability of slopes in relation to different mining sequences. The findings reveal that mining in an upslope direction minimizes disruption to overlying strata. Initiating extraction from lower segments increases tensile-shear stress in coal pillar overburdens, resulting in greater creep deformation towards the downslope than when starting from upper segments, potentially leading to localized landslides and widespread creep deformation in mined-out areas. The downslope upward mining sequence exhibits the least fractal dimensions, indicating minimal disturbance to both strata and surface. While all five mining scenarios maintain good slope stability under normal conditions, recalibrated stability assessments based on fractal dimensions suggest that downslope upward mining offers the highest stability under rainfall, contrasting with the lower stability and potential instability risks of upslope downward mining. These insights are pivotal for mining operations and geological hazard mitigation in multi-seam coal exploitation on bedding slopes.

The Ellipsoidal Surface Method Solving by Integration for Slope Stability Analysis

Landslide is common phenomena in construction field. Nowadays the cylindrical surface method has been used widely to analyze slope stability. However, this method contains two main disadvantages： firstly, the slip surface is assumed to be in circular shape while in fact it is ellipsoid commonly; and secondly, resolve by difference method causing immensely complicated process due to statically indeterminate equations. In this paper, the authors have presented a method that allows transferring of ellipsoid slip surface to cylindrical shape and carries out a single variable equation （by applying integration method）. Also thanks to this method, the current cylindrical surface method has been proved that its application is proper for man-made slopes but usually inappropriate for natural ones. Those results help analysis of slope stability reaching closer to reality.

Stability analysis and monitoring study of Jijia River landslide based on WebGIS

On the basis of in situ investigation and deformation monitoring of the Jijia River landslide （JJRL）, the rigid body limit equilibrium method and finite element method （FEM） were used to analyze the stability of the JJRL; the grey system theory method was applied to forecast the deformation trend of the JJRL; and the information system about the landslide deformation and monitoring, and forecasting systems based on the platform of the Web Geographical Information System （WebGIS） were developed, which can be used to analyze in situ monitoring data and predict the deformation of the landslide. The study results can be summarized as follows： （1） the JJRL is stable as a whole; the water content in the landslide has a great effect on its stability; （2） the developed Web Geographical Information System has realized many functions, including inputting, computing, inquiry, analyzing, and the function of forecasting; it has also realized the functions of distance data management, analysis, and forecasting based on the WebGIS; （3） the information resource can be shared by the WebGIS developed all over the world.

Analysis of Danba Landslide

This paper using finite element method analyzed present slope and contrasted it with the original slope shape, plastic deformation figures and stress changes. At the same time, some deformation figures and stress figures were got, and the potential sliding surface and the stability coefficient were calculated. The conclusions are： This slope is provided with sliding conditions and began to slide when its foot was cut without any support in time. At the foot of the slope, some support measures must be taken to keep the slope steady and the slope surface need to be stabilzed to protect the lower people. These suggestions and conclusions are also useful to the slope constructions and succeeding inspecting works.

Study on high and steep slope stability of surface mine based on RFPA-SRM

The instability and failure mechanism of high and steep slopes in surface mines, and the basis for some reasonable landslide prevention measures were provided using the RFPA-SRM. Based on the actual progress of the Pingzhuang Western Surface Mine and based on strength reduction method, the dynamic instability processes of the top high and steep slope was simulated. Also, the landslide mode was determined, the characteristics of the displacement distribution, the deformation, failure, and the stress distribution in the slope were demonstrated, and the stability was calculated. Conclusions can be drawn as follows： the landslide or failure of high and steep slopes on a surface mine is a gradual process, in which the slope undergoes the generation, expansion, and connection of the fractures and the displacement increases until landslide occurs; a small portion of the upper rocks fail due to the tension and the lower rocks fail due to the shear; the potential sliding surface is combined and the essential cause of the landslide is the shear stress concentration.

Reactivation of a huge ancient landslide by surface water infiltration

An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method(FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7-9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.

Landslide Reliability Analysis Based on Transfer Coefficient Method: A Case Study from Three Gorges Reservoir

To evaluate the reliability of a landslide in a reservoir, the universal transfer coefficient method, which is popularized by the Chinese standard, is adopted as performance function in this study for： （1） common deterministic method stability evaluation; （2） reliability evaluation based on a Monte Carlo method; （3） comparison of landslide reliability under different water levels and under different correlation coefficients between soil shear strength parameters （c, Φ）, respectively with mean, standard deviation, reliability coefficient and failure probability. This article uses the Bazimen （八字门） landslide, which is located at the outlet of Xiangxi （香溪） River in the Three Gorges Reservoir, as an example to evaluate its stability and reliability under different water levels with two-dimensional deterministic and probabilistic methods. With the assumption that constant mean and normal distributed shear strength parameters （c, Φ）, correlation coefficient c, Φ=-1 based reliability analysis, compared with c, Φ=0 and 1, indicates obviously more increase of reliability index and lower standard deviation as water levels rise. To the case of a certain water level, c, Φ=-1 does not have constantly positive or negative effects on landslide reliability compared with c, Φ=0 or 1, but is associated with water level. Whereas the safety factor Fs by deterministic method, which is almost the same value as corresponding mean of safety factor from probabilistic analysis, will increase slightly as water level increases.

Comparative study of material point method and upper bound limit analysis in slope stability analysis

The upper bound limit analysis(UBLA)is one of the key research directions in geotechnical engineering and is widely used in engineering practice.UBLA assumes that the slip surface with the minimum factor of safety(FSmin)is the critical slip surface,and then applies it to slope stability analysis.However,the hypothesis of UBLA has not been systematically verified,which may be due to the fact that the traditional numerical method is difficult to simulate the large deformation.In this study,in order to systematically verify the assumption of UBLA,material point method(MPM),which is suitable to simulate the large deformation of continuous media,is used to simulate the whole process of the slope failure,including the large-scale transportation and deposition of soil mass after slope failure.And a series of comparative studies are conducted on the stability of cohesive slopes using UBLA and MPM.The proposed study indicated that the slope angle,internal friction angle and cohesion have a remarkable effect on the slip surface of the cohesive slope.Also,for stable slopes,the calculation results of the two are relatively close.However,for unstable slopes,the slider volume determined by the UBLA is much smaller than the slider volume determined by the MPM.In other words,for unstable slopes,the critical slip surface of UBLA is very different from the slip surface when the slope failure occurs,and when the UBLA is applied to the stability analysis of unstable slope,it will lead to extremely unfavorable results.

Evaluation of potential surface instability using finite element method in Kharsali Village,Yamuna Valley,Northwest Himalaya

Kharsali village, located in the Northwest Himalaya near the confluence of the Yamuna River and Unta Gad, is situated on a thick(>150 m) paleolandslide deposit. The village is continuously being eroded at its base by the two rivers. Cracks are noted in most houses while the ancient Shani Temple lying to the south of the village has tilted ~5° towards the northeast. Three slope sections(S-1, S-2, S-3) were modelled and analysed to determine the displacement and shear strain patterns of the slopes. Based on surface failure conditions, potential slope instability of the Kharsali village was evaluated from 2D Finite Element Method(FEM) using Shear Strain Reduction(SSR) analysis in the Phase2 software. Results indicate a critical Stress Reduction Factor(SRF) of 1.5 for the southern edge of the village(S-1) housing the Shani Temple. The development of failure surfaces at its lower portion signifies the propagating, progressive nature of the slope. The S-2 slope section is most vulnerable to slope failure, with a critical SRF of 1.08. This has been inferred by the formation of failure surfaces with displacements of 0.05-0.08 m. The S-3 section in the northern part of the Kharsali shows highest critical SRF of 2.76. The un-metalled road section in the north of the village near S-3 hasdeveloped a failure surface with displacement of 0.003-0.004 m, and a zone of subsidence. The S-3 section is relatively stable, whereas the S-2 section is the most vulnerable portion of the village.

地聚物固化黄土力学性能及边坡稳定性研究

研究以中国西北地区近年来黄土路基滑坡为背景.通过击实试验和直剪试验,测得不同地聚物掺量下固化土的试验数据,并通过扫描电镜(SEM)和X射线衍射(XRD)对钢渣-粉煤灰地聚物固化土进行微观结构分析,同时结合pF-Meter仪器测定不同地聚物掺量下固化土的基质吸力与体积含水率.后基于强度折减法,将试验数据代入COMSOL Multiphysics中,通过饱和-非饱和理论的Richards方程,建立固化黄土路基边坡有限元模型.分析降雨前后路基层中地聚物掺入量和坡比对路基边坡的整体稳定性的影响.结果表明:当固化土中地聚物掺入量为25%时,内摩擦角为31.2°,内摩擦角增幅相比于重塑黄土提高了62.5%.随着地聚物掺入量的增加,黏聚力呈现出先升后降的趋势,当地聚物掺入量为20%时达到最高峰,为81.09 kPa,相比于重塑黄土提高了75.86%.路基边坡的稳定性随着地聚物掺入量的增加先上升后下降,随着坡比减小而上升.在特定条件下,边坡稳定性会随着降雨时间的延长而降低,随着降雨强度的增大而减小.

基于双折减系数法与极限平衡法的顺层滑坡稳定性分析

以四川省布拖县龙潭乡冯家坪滑坡为例,利用FLAC3D软件设计了基于双折减系数法的滑坡稳定性分析程序,应用“GIS-Rhino-FLAC3D”耦合技术建立三维地质体模型。考虑黏聚力和内摩擦角在滑坡失稳过程中衰减速度和弱化程度的不同,以及非饱和土中基质吸力对土体抗剪强度的影响,提出一种以黏聚力和摩擦力的衰减权重定义综合安全系数的双折减系数法,并采用极限平衡法作对比计算,研究分析了顺层滑坡的稳定性。结果表明:设计的抗剪强度参数双折减程序可以得出安全系数云图,直观地反映滑坡安全系数的空间分布特征;与传统强度折减法相比,所提出的双折减系数法计算的滑动面分布范围和综合安全系数更精确,较极限平衡法误差更小,可以准确地反映滑坡的稳定状态。研究结果可为双折减系数法应用于滑坡灾害的防治提供参考。

基于Janbu法的边坡整体稳定性滑动面搜索新方法

对于边坡整体稳定分析,找到了一种用随机角来搜索随机滑动面的新方法。在此过程中,采用简化Janbu法计算安全系数。这种新方法产生随机滑动面的过程是:先假定滑动面与边坡上、下缘的交点,在某一初始方向的情况下,以下缘交点为基点开始每随机一个角度方向,使其与对应的滑动体土条划分竖线相交,直到随机角度方向与上、下缘交点的连线重合,将这些交点依次连接,即可得到一条随机曲线(或随机滑动面)。通过随机模拟曲线,发现随机角物理意义明确,具有以下两个独特优点:①只有一个随机条件,随机因素易于控制,便于计算机编程;②为保证其随机曲线为一光滑曲线,可对随机角进行适当优化,并且在条分数足够大时,能够模拟任何曲线。针对以往随机搜索精度不高的问题,采用近似曲线来代替随机曲线的方法加以改进,并且将近似曲线的生成进行了简化。经各种实例对比分析后,得出此方法计算得出的安全系数与以往研究成果颇为接近,得到的最危险滑动面亦与实际情况相符,因而可说明此方法能够适用于边坡整体稳定性分析。

滑坡推力计算的改进Janbu法

滑坡推力是边坡治理工程的基础资料。本文探讨了通过改进 Janbu法来计算滑坡推力 ,并进行了详细推导。应用表明 :它不但可以指出推力分布情况 ,同时也指明了治理工程的部位及其应提供的抗力大小 ;改善坡体的强度参数 ,对于减小推力也是有益的。

基于椭球滑动体假定和三维简化JANBU法的边坡稳定分析

采用一般椭球体模拟三维土坡的滑动体,利用三维简化JANBU法计算其安全系数,该法假定各个条柱底面的滑动方向在水平面上的投影相等,借此可用一个变量来表达各个底滑面的滑动方向,简便易行。此外,综合借鉴粒子群优化算法和和声算法的优点,提出了改进的粒子群算法,并利用对2个三维土坡的最危险滑动体进行了搜索,与已有结果进行了对比分析,表明方法是可行有效的。

大型水库区桥基边坡稳定性与失稳运动特征

我国西南山区已建成众多大型水库,库岸边坡在降雨、库水周期性涨落、地震等复杂地质条件作用下易发生滑坡。若公路桥梁基础位于库岸边坡变形或失稳影响范围内,可能对桥墩产生巨大的侧向荷载,从而危害基础结构乃至桥梁整体安全,而针对该问题研究较少。以白鹤滩库区小江特大桥桥基边坡为例,应用GeoStudio分析桥基边坡在库水涨落、降雨、地震联合作用下的稳定性;针对库水涨落联合降雨工况下的欠稳定边坡,采用TsunamiBalls(TB)数值方法模拟滑坡堆积体失稳下滑冲击桥墩的动力学过程,分析桥墩受到的动态冲击荷载。研究表明:(1)库水升降是影响边坡稳定性的主要因素;(2)施加地震荷载后边坡稳定性系数大幅降低,而降雨对稳定性系数影响有限;(3)滑体对桥墩的冲击荷载随时间先增大再减小,期间会出现3次主要荷载峰值,其中最大冲击荷载13890kN,出现在滑体最大运动速度之后,滑体冲击质量最大的时刻。库岸桥基边坡在库水位涨落条件下稳定性明显降低,TB模拟滑体失稳冲击过程可能造成桥基结构破坏。研究结果可为大型水库边坡和公路桥梁防灾减灾及安全运营提供技术参考。

熵权法改进的模糊数学滑坡稳定性评价方法研究

滑坡是中国最为常见的一种地质灾害类型,其具有的易发、频发特点使得人民的生命财产安全受到了严重的威胁,滑坡的稳定性评价是滑坡防灾减灾工作中最为关键的一项工作。鉴于滑坡诱发因素具有模糊性的特点,文章以陕西省勉县新铺镇发育的典型堆积层滑坡为例,在地质环境条件分析的基础上,考虑了采用模糊数学法进行滑坡稳定性评价,并引入热力学中“熵”的概念,采用熵权法确定了滑坡诱发因子的权重,进而提出了一种基于熵权法改进的模糊数学滑坡稳定性评价新方法。结果表明:新提出的基于熵权法改进的模糊数学滑坡稳定性评价方法克服了传统模糊综合评价方法主观性判断滑坡影响因子权重的弊端;通过数值模拟法进行滑坡稳定性定量化分析验证,发现两种方法评价结论较为吻合,说明了所提出的新方法具有一定的可靠性。基于熵权法改进的模糊数学滑坡稳定性评价方法较为快速简捷,可用于临灾快速预警、应急救援等突发情况下的滑坡防灾减灾工作。