New risk assessment methodology for coal mine excavated slopes

This paper presents a new risk assessment methodology for coal mine excavated slopes. This new empirical-statistical slope stability assessment methodology(SSAM) is intended for use by geotechnical engineers at both the design review and operational stages of a mine's life to categorise the risk of an excavated coal mine slope. A likelihood of failure is determined using a new slope stability classification system for excavated coal mine slopes developed using a database of 119 intact and failed case studies sourced from open cut coal mines in Australia. Consequence of failure is based on slope height and stand-off distance at the toe of the excavated slope. Results are presented in a new risk matrix, with slope risk being divided into low, medium and high categories. The SSAM is put forward as a new risk assessment methodology to assess the potential for, and consequence of, excavated coal mine slope failure.Unlike existing classification systems, assumptions about the likely failure mode or mechanism are not required. Instead, the SSAM applies an approach which compares the conditions present within the excavated slope face, with the known past performance of slopes with similar geotechnical and geometrical conditions, to estimate the slope's propensity for failure. The SSAM is novel in that it considers the depositional history of strata in an excavated slope and how this sequence affects slope stability. It is further novel in that it does not require explicit measurements of intact rock, rock mass and/or defect strength to rapidly calculate a slope's likelihood of failure and overall risk. Ratings can be determined entirely from visual observations of the excavated slope face. The new SSAM is designed to be used in conjunction with existing slope stability assessment tools.     

Rapid and robust slope failure appraisal using aerial photogrammetry and 3D slope stability models

Slope failures are an inevitable aspect of economic pit slope designs in the mining industry. Large open pit guidelines and industry standards accept up to 30% of benches in open pits to collapse provided that they are controlled and that no personnel are at risk. Rigorous ground control measures including real time monitoring systems at TARP(trigger-action-response-plan) protocols are widely utilized to prevent personnel from being exposed to slope failure risks. Technology and computing capability are rapidly evolving. Aerial photogrammetry techniques using UAV(unmanned aerial vehicle) enable geotechnical engineers and engineering geologists to work faster and more safely by removing themselves from potential line-of-fire near unstable slopes. Slope stability modelling software using limit equilibrium(LE) and finite element(FE) methods in three dimensions(3D) is also becoming more accessible, user-friendly and faster to operate. These key components enable geotechnical engineers to undertake site investigations,develop geotechnical models and assess slope stability faster and in more detail with less exposure to fall of ground hazards in the field. This paper describes the rapid and robust process utilized at BHP Limited for appraising a slope failure at an iron ore mine site in the Pilbara region of Western Australia using a combination of UAV photogrammetry and 3D slope stability models in less than a shift(i.e. less than 12 h).     

公路隧道正交下穿边坡与软弱夹层围岩稳定性分析

为分析山岭地区公路隧道-正交体系下，围岩内含软弱夹层导致施工过程易发生衬砌变形开裂甚至隧道塌方等问题，以某隧道边坡拟扩建公路为工程背景，基于抗拉剪强度折减法理论，采用FLAC^3D有限差分软件，研究不同边坡坡度和隧道埋深对该隧道-边坡围岩稳定性和安全系数的变化规律。结果表明：随着边坡坡度的不断增大，围岩最大剪切应变数值和分布范围逐渐增大，塑性区范围不断增大，围岩稳定性安全系数不断减小。随着隧道埋深的增大，围岩最大剪切应变数值先增大再减小后增大，但剪切应变范围不断增大，塑性区范围不断增大，围岩稳定性安全系数呈现先减小再增大。当无软弱夹层时计算的安全系数最大，当存在软弱夹层时，采用非同步折减法理论计算的安全系数比同步折减法较高。     

临河岩质边坡地震抗倾覆稳定性拟动力分析

基于拟动力法推导出不同工况条件下临河岩质边坡地震抗倾覆稳定安全系数计算公式。通过参数分析,研究不同岩体放大系数下,水平和垂直地震力、张裂缝积水深度、边坡超载、锚固效应、流水淘蚀等对岩质边坡地震抗倾覆稳定性的影响,研究表明,不同工况下,张裂缝积水深度、水平地震力、流水淘蚀不利于岩质边坡地震抗倾覆稳定,但竖向地震力、锚固力、锚固高度、坡顶超载等有利于岩质边坡地震抗倾覆稳定;随着岩体放大系数的增加,水平地震力、竖向地震力对岩质边坡抗倾覆稳定性的影响增大,坡顶超载、张裂缝积水深度、锚固应力、锚固高度、临河水位对岩质边坡抗倾覆稳定性的影响减小,而锚固倾角、坡脚淘蚀高度对边坡抗倾覆稳定性的影响基本不变。     

黄土高原边坡特征与破坏规律的分区研究

为了研究黄土高原自然边坡的特征及破坏规律,按山系与水系或水系的分水岭、地貌单元、地层岩性特征等条件,将黄土高原划分为8个区：临洮—永靖区、天水—通渭区、兰州—会宁区、陇东区、靖边—安塞区、隰县—离石区、甘泉—吉县区和汾渭区。根据极限状态边坡的4个野外判别标准,测量了8个区510个自然极限状态黄土边坡断面,分区采用指数模型回归边坡坡高与坡宽的相关关系,计算各区20、50、100m坡高的边坡稳定系数和失效概率。结果表明：黄土高原的边坡特征与破坏形式具有分区特征,且南北差异性明显。临洮—永靖区边坡坡高与坡宽呈线性关系,表明该区边坡坡度不随坡高变化,边坡稳定性受内摩擦角控制;兰州—会宁区和靖边—安塞区高坡陡,低坡缓,高坡不稳定,易发生错落式滑坡;天水—通渭区、甘泉—吉县区和汾渭区高坡缓,低坡陡,稳定性计算结果显示高坡和低坡都较为稳定,但由于地层结构和地貌的特点,高边坡易发生低速蠕变型滑坡或高速远程滑坡;陇东区边坡整体上较为稳定;隰县—离石区受黏粒含量较高的Q1地层控制,高边坡稳定性较差;50m左右坡高的黄土边坡稳定性对强度指标内聚力、内摩擦角的敏感度都高,易于失稳。     

Methods applied in Australian industry to evaluate coal mine slope stability

Strata failure is a principal hazard in open cut coal mining as it has the potential to cause multiple fatalities. Prior to the excavation of any slope, a geotechnical assessment should review the likely slope performance, including the risk of slope failure. Controls to manage this risk to an acceptable level should accompany the geotechnical analysis. A survey of 43 practising geotechnical engineers indicated that kinematic and 2D limit equilibrium analyses were the methods most commonly applied to analyse excavated slope stability. While these methods are well established and widely applied in the broad rock engineering disciplines(e.g. civil, hard rock), a recent review of over 60 slope failures suggests these methods have limited suitability for modelling the complex failure mechanisms observed in excavated coal mine slopes. Kinematic techniques do not adequately capture the rock mass component of excavated slope failure and do not provide a geospatial location of potential failure, while 2D limit equilibrium techniques do not adequately capture the 3D mechanisms of excavated slope failures. Methods which do consider the 3D mechanisms of slope failure are summarized for industry consideration and application.     

Quantitative hazard assessment system(Has-Q) for open pit mine slopes

Rock slope hazard assessment is an important part of risk analysis for open pit mines. The main parameters that can lead to rock slope failures are the parameters traditionally used in geomechanical classifications, the slope geometrical parameters and external factors like rainfall and blasting. This paper presents a methodology for a hazard assessment system for open pit mine slopes based on 88 cases collated around the world using principal components analysis, discriminant analysis and confidence ellipses. The historical cases used in this study included copper, gold, iron, diamond, lead and zinc, platinum and claystone mines. The variables used in the assessment methodology are uniaxial compressive strength of intact rock; spacing, persistence, opening, roughness, infilling and orientation of the main discontinuity set; weathering of the rock mass; groundwater; blasting method; and height and inclination of the pit. While principal component analysis was used to quantify the data, the discriminant analysis was used to establish a rule to classify new slopes about its stability condition. To provide a practical hazard assessment system, confidence ellipses were used to propose a hazard graph and generate the HAS-Q. The discriminant rule developed in this research has a high discrimination capacity with an error rate of11.36%.     

Stability analysis of the sliding process of the west slope in Buzhaoba Open-Pit Mine

To study the stability of the west slope in Buzhaoba Open-Pit Mine and determine the aging stability coefficient during slide mass development, the deformation band of the west slope and the slide mass structure of the 34,600 profile are obtained on the basis of hydrology, geology, and monitoring data.The residual thrust method is utilized to calculate the stability coefficients, which are 1.225 and 1.00 under sound and transfixion conditions, respectively. According to the rock damage and fragmentation and the principle of mechanical parameter degradation, the mechanical models of the slide mass development of the hard and soft rock slopes are established. An integrated model for calculating the slope stability coefficient is built considering water, vibration, and other external factors that pertain to the structural plane damage mechanism and the generating mechanism of the sliding mass. The change curve of the stability coefficient in the slide mass development is obtained from the relevant analyses,and afterwards, the stability control measures are proposed. The analysis results indicate that in the cracking stage of the hard rock, the slope stability coefficient decreases linearly with the increase in the length Lbof the hard rock crack zone. The linear slope is positively correlated to rock cohesion c. In the transfixion stage of the soft rock, the decrease speed of the stability coefficient is positively correlated to the residual strength of the soft rock. When the slope is stable, the stability coefficient is in a quadratic-linear relationship with the decreased height Dh of the side slope and in a linear relationship with anchoring force P.     

甘肃天水地区黄土极限状态边坡的统计分析

在实际工程边坡设计中,往往参考临近自然边坡的坡率设计来进行人工开挖边坡。基于这种工程类比法,现场实测甘肃天水地区51个坡高40～150 m的黄土极限状态边坡断面,获得其坡高、坡宽及坡度参数,统计发现坡高与坡宽符合双对数线性关系,建立二者的相关方程;再将坡高按10m间距分段,每个坡高段取3个极限坡高,利用Morgenstern-Price法反演了不同坡高段的强度参数(内聚力和内摩擦角)。由反演结果发现,随着坡高的增大,黄土的综合内聚力增大,内摩擦角减小,此特点与黄土强度参数值随所处深度的变化规律基本一致。基于反演的强度参数和极限状态边坡坡高与坡宽的回归方程,进一步计算获得不同稳定系数下的坡高与坡宽的关系曲线,将该曲线制成图,可用来直接判定一个已知边坡的稳定系数,也可以用来确定拟设计边坡的坡度。     

基于连续-非连续方法的高填方边坡变形稳定性分析

为研究高填方边坡的稳定性,基于连续-非连续耦合分析理论,采用边界墙耦合方法建立了高填方边坡的连续-非连续耦合分析模型,利用强度折减的方法来简化降雨工况,参照实际滑坡工程案例,土体参数应折减15%,进行了降雨影响下的高填方边坡稳定性分析;对细观参数进行折减,求解得到边坡的安全系数为1.60,分析了边坡在极端工况下可能的变形破坏情况。通过该案例探究了连续-非连续耦合方法进行边坡稳定性分析的可行性。结果表明,连续-非连续耦合方法能够快速高效且直观地评估高填方边坡的稳定性。     

大冶铁矿东露天采场边坡破坏判据的研究

通过对大冶铁矿东露天采场F9,F13断裂带内边坡的深入研究,从整体与局部稳定性系数等方面探讨了边坡破坏判据．利用有限元强度折减法和极限平衡法计算边坡的体稳定性,得出边坡处于极限平衡状态时的塑性应力及塑性应变,提出边坡破坏判据．     

不同含石率及基覆岩层倾角下土石混合体边坡稳定性分析

为准确地分析土石混合体边坡的稳定性，提出了一种可考虑不同块石含量、块石随机分布及基覆岩层倾角的边坡稳定性分析方法。该方法根据土石混合体边坡中的块石含量、级配以及基覆岩层倾角，随机生成了含石率从10%～60%、基覆岩层倾角从0°～20°的边坡模型，每种含石率及基覆岩层倾角均考虑8个不同的块石分布位置，最后将生成的模型导入到Optum G2中建立土石混合体边坡模型，采用有限元极限分析法对该类型边坡的稳定性进行了分析，并将计算结果与采用Kalender等效强度参数模型所得的结果进行了对比验证。研究结果表明，由于块石空间分布位置的不同，相同含石率及基覆岩层倾角下土石混合体边坡的最大、最小下、上限安全系数变化较大；相同含石率下，随着基覆岩层倾角的增加，边坡的下、上限安全系数的平均值变化相对较小；土石混合体边坡坡体中的剪切带呈现出“绕石”、“分流”以及“包含”这3种典型的扩展模式；通过将本文方法与Kalender等效强度参数模型所得的安全系数进行的对比分析，验证了作者所提方法的可行性。研究结果可为土石混合体边坡的设计及施工提供参考依据。     

矿山采洞与软弱带相对位置对边坡稳定性的影响分析

以陕西某滑坡为例,采用非连续变形(DDA)理论,研究沿岩层平行分布的采洞组与软弱带相对位置对边坡稳定性的影响。在对滑坡特征、基本地质条件与力学参数进行调查研究的基础上,建立滑坡实际模型进行计算分析。分析结果表明,采空区群会影响坡体内应力场,且其与软弱带相对位置的改变会影响坡体稳定性。当采空区群距软弱带为采空区高的2~5倍时会降低坡体的稳定性,而当采空区距软弱带为采空区高度5~6倍时,最为危险,之后影响随着距离增大而降低,当采空区距软弱带大于采空区高度的8倍时坡体稳定。     

岩质边坡锚杆框架梁加固的有限元分析

针对石家庄至武汉铁路客运专线岩质边坡,采用有限元数值计算方法分析了锚杆（索）框架梁加固岩质边坡的受力情况.得到了边坡位移场和应力场分布规律和锚杆（索）轴向力的大小.计算结果表明：实际工程中采用锚杆、预应力锚索加抗滑桩这种新型的复合式支护结构能有效地限制边坡的水平位移,提高边坡的稳定性,锚索的布置和预应力设计值大小显著影响坡体内部的位移及应力场分布,研究结论对岩质边坡的工程设计具有一定的借鉴意义.     

白云鄂博主矿边坡岩体全方位RQD指标的确定及其三维图形显示

在三维岩体结构模拟的基础上 ,给出了白云鄂博主矿边坡岩体全方位RQD指标变化的三维图形 ,据此可以很清楚地看出边坡岩体结构的各向异性情况 ,为边坡工程后续工作提供了一个准确而形象的地质信息     

基于强度折减法的不同坡角边坡稳定性分析

介绍了强度折减法的基本原理,在此基础上运用强度折减法分析边坡坡角对边坡稳定性的影响,运用ANSYS软件模拟不同坡角的边坡,分析计算不同坡角边坡的安全系数,通过计算得出不同坡角边坡围岩极限破坏时的折减强度参数,分析研究边坡坡角与边坡安全系数F、边坡围岩极限破坏凝聚力c’及极限破坏摩擦角‘φ’之间的关系。     

Stability and reliability of pit slopes in surface mining combined with underground mining in Tonglushan mine

Slope stability is of critical importance in the process of surface-underground mining combination. The influence of underground mining on pit slope stability was mainly discussed, and the self-stabilization of underground stopes was also studied. The random finite element method was used to analyze the probability of the rock mass stability degree of both pit slopes and underground stopes. Meanwhile, 3D elasto-plastic finite element method was used to research into the stress, strain and rock mass failure resulting from mining. The results of numerical simulation indicate that the mining of the underground test stope has certain influence on the stability of the pit slope, but the influence is not great. The safety factor of pit slope is decreased by 0.06, and the failure probability of the pit slope is increased by 1.84%. In addition, the strata yielding zone exists around the underground test stope. The results basically conform to the information coming from the field monitoring.     

Determination of the Stable Slope Configuration of Oval-Shaped Furrow Pits

The space effects of oval-shoped furrow pit slopes were analyzed by the elastic mechanics principle. The interaction of limit equilibrium slope angle, friction coefficient, cohesion and horizontal radius of oval-shaped furrow, pits has been derived. The oral trumpet-like rock mass is homogeneous and elastic while only loaded by its dead weight. The interaction indicates that the deeper an oral-shaped furrow pit is excavated, the greater the limit equilibrium slope angle. Both the theory base for reducing stripping waste rock in an oval- shaped furrow pit and the basic way to determine the configuration of a stable slope were developed from the mentioned interaction.The theory includes the preceding principles of stability analysis of slopes. Compared with the configuration determined by traditional theory of slope stability, a great quantity of stripping waste rock can be reduced by that determined in this paper trader stable conditions.     

空间与颗粒参数对块石土边坡稳定性影响数值模拟研究

块石土边坡具有物理力学性质复杂,非线性强等特性,受块石-土体空间分布、块石粒径等几何因素影响较大。为研究几何参数对块石土边坡稳定性影响,本文基于研究团队提出的块石形状数据库随机生成方法,采用ABAQUS软件非线性分析方法,考虑含石量、最大粒径、空间分布等多种几何因素,建立大量有限元模型进行计算分析,得到以下结果：含石量增大,边坡安全系数上升,且含石量在50%-60%这个区间是上升速率最快。含石量增大,同粒径组边坡安全系数标准差增大,模型安全系数差异变大;最大粒径增大,块石分布对于边坡安全系数的影响增大,边坡稳定性先减小后增强,同粒径组边坡安全系数标准差增大。含石量和最大粒径增大,块石空间分布对于边坡稳定性影响增大。粒径大小不同,块石空间分布对于块石土边坡稳定性影响方式也不同,大粒径块石存在令滑动面向边坡内部发展,而密集小粒径块石大多是令滑面呈折线形,二者皆可增大边坡稳定性;当块石长轴与坡面夹角为90°、135°时,边坡塑性区呈发散分布,滑面更靠内部,稳定性更好,而当块石长轴与坡面夹角为0°、45°,则与上述情况相反;在通常沉积条件下,边坡稳定性随长短轴比增加而降低,滑动面越发平滑,塑性区范围与更加集中。可以看出,含石量、块石粒径、空间分布等因素对于块石土边坡有很大影响。几何参数不同,边坡稳定性差异较大,且具有一定规律性,在实际工程中有一定参考价值。     

Pull-out tests and slope stability analyses of nailing systems comprising single and multi rebars with grouted cement

The pull-out capacities for soil nailing systems comprising of one single 29 mm diameter (type A) and four 16 mm diameter (type B) rebars with grouted cement were examined. A field test and numerical analysis for the type A and type B systems were carried out to investigate the pull-out capacities and the slope stability reinforcement efficiency in soil and rock slopes. The results of the pull-out tests show the mobilized shear force and load transfer characteristics with respect to soil depth. The load-displacement relationship was examined for both type A and type B systems. Slope stability analyses were carried out to study the relationships between soil and nail reinforcement and bending stiffness as well as combined axial tension and shear forces. Factors of safety were calculated in relation to the number of nails and their outside diameters. Both soil and rock slopes were included in this evaluation.