Application of rock mass classification systems to rock slope stability assessment: A case study

The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to many factors such as adverse slope geometries, geological discontinuities, weak or weathered slope materials as well as severe weather conditions. External loads like heavy precipitation and seismicity could play a significant role in slope failure. In this paper, several rock mass classification systems developed for rock slope stability assessment are evaluated against known rock slope conditions in a region of Saudi Arabia, where slopes located in rugged terrains with complex geometry serve as highway road cuts. Selected empirical methods have been applied to 22 rock cuts that are selected based on their failure mechanisms and slope materials. The stability conditions are identified, and the results of each rock slope classification system are compared. The paper also highlights the limitations of the empirical classification methods used in the study and proposes future research directions.     

Slope stability assessment of an open pit using lattice-spring-based synthetic rock mass (LS-SRM) modeling approach

Discontinuity waviness is one of the most important properties that influence shear strength of jointed rock masses, and it should be incorporated into numerical models for slope stability assessment. However, in most existing numerical modeling tools, discontinuities are often simplified into planar surfaces. Discrete fracture network modeling tools such as MoFrac allow the simulation of non-planar discontinuities which can be incorporated into lattice-spring-based geomechanical software such as Slope Model for slope stability assessment. In this study, the slope failure of the south wall at Cadia Hill open pit mine is simulated using the lattice-spring-based synthetic rock mass (LS-SRM) modeling approach. First, the slope model is calibrated using field displacement monitoring data, and then the influence of different discontinuity configurations on the stability of the slope is investigated. The modeling results show that the slope with non-planar discontinuities is comparatively more stable than the ones with planar discontinuities. In addition, the slope becomes increasingly unstable with the increases of discontinuity intensity and size. At greater pit depth with higher in situ stress, both the slope models with planar and non-planar discontinuities experience localized failures due to very high stress concentrations, and the slope model with planar discontinuities is more deformable and less stable than that with non-planar discontinuities.     

A preliminary design approach for guledar irrigation dam project

This paper describes the results of engineering geological and rock mechanics studies carried out at the Güledar irrigation dam project. Project is designed to regulate the drainage and to irrigate the agricultural areas. The dam site is located within Güledar Sirkeli formations composed of sandstone, limestone and diabase. Studies maintained both at field and laboratory. Field studies included geological mapping, core drilling, sampling for laboratory testing, pressurized water tests, and intensive discontinuity surveying. Some physical and mechanical properties were determined at laboratory. The rock mass qualities of rock units were determined, and described as poor to fair quality. The corresponding Hoek and Brown failure envelopes have been drawn and failure equations have been suggested for stability analysis of dam foundation, slope stability and diversion tunnels for each rock unit.     

Traitement d’image appliqué aux matériaux: Exemple d’une analyse quantitative des feldspaths dans les roches

Mechanical properties of Neogene sedimentary soft rocks and their discontinuities are deteriorated by environmental changes, such as wetting and stress release. In addition, the reliable estimation of shear strength of weakness planes in these rocks is a common problem. This paper aims to characterize the engineering properties of weak, stratified, clay-bearing coal measures encountered in surface coal mining in southwest Turkey with special reference to the shear strength of their discontinuities and weak zones which are of particular significance in determining slope stability. The results obtained from a series of laboratory shear tests carried out on specially prepared bulk samples containing natural discontinuities and weak zones were compared with values, which resulted from tests on similar weakness planes in another pit and back-analyses of instabilities experienced in two mines, for further design considerations.     

Testing of rock joints filled with gouge using a triaxial apparatus

The rock mass contains discontinuities and its instability depends on the geometry of these discontinuities and the slope and orientation of the excavated face. One of the most important factors is the shear strength of potential failure planes. The characterisation of a discontinuity or a shear zone is not possible merely by visual examination of a specimen nor by subjecting it to conventional laboratory testing. The combined effects of the shear zone, its stress–strain history and the resulting strength deformation relation modulate the behaviour of rock mass, particularly when it approaches the state of limit equilibrium.This paper presents a testing technique for rock joints filled with gouge of various thicknesses (t=5–30 mm), dip angle (β=5–50°) and at strain rate (e=5–80 mm/h) in a triaxial testing system. The results of unconsolidated undrained tests carried out in triaxial conditions both for undulating and planar types of joints filled with gouge are reported. Extensive experimental results provided an insight into the development of a constitutive relation to predict strength criteria of discontinuous rock masses.     

结构面的剪切蠕变特性及本构模型研究

岩体结构面的蠕变特性研究对解决岩石力学实际问题具有很重要的意义,结构面的蠕变力学性态往往控制着岩体的时效变形和长期强度,研究结构面的剪切蠕变特性是岩石流变学的一项重要内容。通过规则齿形结构面在不同法向应力条件下的剪切蠕变试验,研究了不同角度结构面的剪切蠕变特征,并根据蠕变试验结果,对结构面的剪切蠕变特性进行了描述,对结构面剪切蠕变试验过程中的蠕变速率特性进行了研究。研究表明,结构面在蠕变试验过程中,严格意义下的稳态蠕变是不存在的,常说的稳态蠕变实际上是蠕变速度随时间缓慢减小的近似稳态蠕变过程。最后,提出改进Burgers模型来描述蠕变的剪切蠕变特性,并讨论了改进的Burgers模型对于描述结构面剪切蠕变特性的适用性。     

边坡及洞室岩体的全空间块体拓扑搜索研究

 在一定空间区域内,由三维有限长的随机结构面及确定性结构面切割形成的所有块体的搜索问题,即全空间块体搜索问题,是裂隙岩体研究中十分重要的基础性课题。在随机结构面切割下全空间块体拓扑搜索一般方法研究基础上,进行边坡及洞室岩体的全空间块体搜索问题研究。给出计算分析过程,包括三维结构面网络模拟、结构面与边界面之间的交线分析、封闭回路分析、回路空间位置分析、孤立回路删除、相关回路分析以及封闭块体搜索等,并对其中的结构面与边界面交线求解进行重点讨论。对块体切割中出现的简单凸多面体及凹多面体、坑体、环体、腔体等4种块体类型进行分析,基于单连通和复连通回路的不同特点,讨论如何统一地对4种块体类型进行搜索分析,从而实现边坡/洞室岩体的全空间块体拓扑搜索技术。在此基础上,基于经典的块体理论,实现边坡/洞室工程中的块体渐进失稳分析技术。最后,针对边坡和洞室算例进行分析和讨论。     

金川露天矿边坡变形机制及过程

本文介绍了金川露天矿边坡滑动-倾倒复合变形实例,它是在两种机制共同作用下发生的。岩体条块状碎裂结构对变形机制和发展过程起了控制作用。岩体结构的变形特性基本上符合蠕变三阶段发展规律,变形和时间呈幂函数曲线关系。岩体变形在本质上主要是其断层蠕变和结构面的剪切和开裂。岩体蠕变特性是岩体结构效应和时间效应的综合体现。     

绿片岩软弱结构面的剪切蠕变特性研究

 针对锦屏II级水电站引水隧洞超埋深、高地应力的特点,选取边坡和地下洞室围岩中含有绿片岩软弱结构面的灰白色大理岩为研究对象,对含有软弱结构面的大理岩试样进行分级加载剪切流变试验,并对试验结果进行分析,探讨软弱结构面的蠕变特性。通过对不同法向应力条件下岩体结构面的蠕变力学特性及其规律的研究,以及对结构面剪切蠕变试验过程中的蠕变速率特性进行分析,结果显示结构面的剪切蠕变试验曲线表现出明显的3个阶段。在此基础上选用改进的Burger模型对结构面蠕变试验结果进行拟和分析,并讨论改进的Burger模型对于描述结构面剪切蠕变特性的适用性。     

Geotechnical characteristics of Bakhtiary dam site,SW Iran: the highest double-curvature dam in the world

The Bakhtiary Hydropower Project with a 325 m high dam will be constructed on Bakhtiary River, in southwest Iran. The main dam has been designed as a double-curvature concrete structure which will be the highest one of its type in the world. Geologically, the dam site is located on siliceous limestone of the Sarvak Formation in the northwestern part of the folded Zagros. A large number of complicated geological structures in the study area, such as folding and duplex structure, faults, chevron folds, kink band zones as well as joint and fracture systems, raised concerns regarding the acceptability of the site for such a monumental dam. To create a comprehensive geotechnical model of the dam site and appurtenant structures, very extensive surface and subsurface investigations were carried out, including core drilling, water pressure testing, driving exploratory galleries for engineering geological mapping, a rock mass discontinuity survey and in situ rock mechanical tests. This research applies the results of the engineering geological and geotechnical investigations to define the geomechanical model of the dam site enabling options to be considered to achieve a safe dam design. The investigations show the rock mass of the dam site area is intersected by four main discontinuities namely, the bedding plane(s) of the rock mass and three major joint sets. Water pressure tests provide data about the permeability of the rock mass which is significantly dependant on the joint properties and the geological structures. These parameters, set the criteria for the design of the grout curtain at the dam foundation. The rock mass classification of the dam site was determined mainly based on the gallery survey and core logging using the rock mass rating, geological strength index (GSI) and Q system. Six classes of rock mass qualities were distinguished which show a fair to good rock mass at the dam foundation. From the plate load test results, a site-specific correlation was developed for estimating the modulus of deformation of the rock masses using GSI value. The estimated engineering geological and geotechnical parameters at the dam site are generally favorable and suitable for the safe design of the Bakhtiary arch dam with a height of 325 m.     

深废矿坑高陡边坡极限承载力计算方法研究

针对深废矿坑高陡边坡极限承载力问题,综合考虑锚索锚固岩体的压力墙和组合梁作用,结合Hoek-Brown强度准则,采用特征线法推导得到了矿坑高陡边坡极限承载力计算方法。结合工程实例,就坡度α、岩石力学参数GSI、m₀以及锚索的主动支护力等影响因素对矿坑岩壁岩石地基极限承载力的影响进行了分析,研究表明：(1)承载力系数随坡度的增加呈线性降低,当GSI为45、m₀为7时,也即矿坑岩壁岩体为质量较差的石灰岩时,加锚后其承载力约为加锚前承载力的1.32～1.54倍,考虑锚索的组合梁作用可作为安全储备;(2)随着岩体质量越来越好,地基极限承载力系数增长的幅度越来越大,当坡度α为60°、GSI取85,坑壁为好岩体时,承载力系数值为1.28;GSI取45,坑壁为较差岩体时,承载力系数值为0.23;前者约为后者的6倍,表明岩体质量指标的好坏对承载力的影响较大。     

露天边坡与山坡复合体变形随机介质预测方法的研究

露天边坡岩体工程开挖 ,将使周边岩体产生移动和变形 ,从而严重地威胁着边坡本身及周边环境的安全。应用随机介质理论方法建立了岩体开挖量对变形影响大小的预测模型 ;并依据实例对移动参数进行了回归分析 ,然后 ,对后续开挖将产生的变形值大小进行预测 ,为安全生产提供决策依据     

基于无人机技术获取岩体结构面信息方法研究

岩质边坡的稳定性主要取决于坡体内部结构面的发育特征和性质。获取边坡岩体内部结构面的几何信息,特别是产状数据,对于研究结构面的组合规律及进一步评价边坡的稳定性具有非常重要的意义。传统的结构面采集方法工作效率极低,且对于高陡岩质边坡,技术人员无法到达。无人机摄影测量技术具有非接触、高效率的突出优势,能够有效弥补传统方法的不足。以长春市某高陡岩质边坡为研究对象,使用无人机进行航空影像数据采集,建立边坡的三维实景模型,并提取结构面产状数据。经与现场实测代表性结构面产状数据对比可知,新方法的精度较高。该方法为快速准确评价高陡岩质边坡稳定性提供了依据。     

单锚及群锚失效对边坡稳定性影响的模型试验研究

针对典型岩土体边坡,通过室内模拟试验,研究锚力变化或锚失效在群锚中引起的荷载转移现象,探讨群锚失效后边坡稳定性的劣化过程、失稳形态以及坡面设置格子梁对锚索张力及边坡稳定性的影响等问题。群锚抑制坡体的变形效应,可使岩体均匀性、整体性加强,增加韧性和承受大变形而不破坏的能力。群锚中某一锚索锚力变化会导致其承担的荷载在群锚内部发生较明显的转移现象,结构面压缩带同时被削弱,结构面的整体安全度降低;某一锚索的失效也会引起相邻锚索接连失效的多米洛效应,导致边坡稳定性急剧降低。坡面施加格子梁结构可调动坡面更大范围岩土体发挥自承能力,分担锚索承担的部分荷载,改善边坡的稳定性。岩坡加固设计中应注意格子梁结构强度与锚索锚固力相匹配。     

规则岩体结构面的蠕变特性研究

 岩体结构面的蠕变特性研究对解决岩石力学实际问题具有很重要的意义。通过规则齿型结构面在剪切应力条件下的双轴蠕变试验,研究不同爬坡角的结构面在不同法向应力时的蠕变特性,并根据蠕变试验结果,得到结构面剪切蠕变、法向蠕变随法向应力、剪应力、爬坡角的变化规律和时效性,并选取Burgers模型来描述蠕变的剪切变形特性。在模型试验的基础上采用三维有限元程序对具有锯齿状结构面的水泥砂浆块体在荷载作用下的受力性状进行模拟分析。通过有限元分析,探讨规则齿状结构面的应力分布规律。利用ANSYS计算结果,通过最大正应力理论对结构面的破坏进行判别,从而验证在剪切试验中,齿面以拉断形式破坏。     

Factor of safety of strain-softening slopes

Stability analysis of strain-softening slopes is carried out using the shear strength reduction method and Mohr-Coulomb model with degrading cohesion and friction angle.The e ffect of strain-softening behavior on the slope factor of safety is investigated by performing a series of analyses for various slope geometries and strength properties.Stability charts and equations are developed to estimate the factor of safety of strain-softe ning slopes from the results of traditional stability analysis based on perfectly-plastic behavior.Two example applications including an open pit mine in weak rock and clay shale slope with daylighting bedding planes are presented.The results of limit equilibrium analysis and shear strength reduction method with perfectly-plastic models were in close agreement.Using perfectly-plastic models with peak strength properties led to overly optimistic results while adopting residual strength properties gave excessively conservative outcomes.The shear strength reduction method with a strain-softening model gave realistic factors of safety while accounting for the process of strength degradation.     

基于轴比论的椭圆形深凹露天矿稳定性边坡形状确定方法研究

 假设岩体为连续、均质、各向同性的弹性体,承受自重应力和水平地应力联合作用,在对其进行椭圆形喇叭曲面开挖情况下,取椭圆形喇叭曲面边坡上一椭圆岩环作为力学模型,结合轴比论,推导出椭圆形深凹边坡环向应力表达式。借鉴巷道最稳定高宽轴比的确定方法,由莫尔–库仑强度理论,求解边坡安全系数。根据边坡微元体临界下滑条件,确定临界稳定性边坡角,从而得到此时的边坡形状。与传统的稳定性理论确定的边坡形状相比,该边坡形状可在保证边坡稳定的前提下减少巨大的废石剥离量。     

Stability evaluation and optimal excavated design of rock slope at Antaibao open pit coal mine, China

Rock slope deformation stability for Antaibao open pit coal mine under mining was analyzed using finite difference technique (FLAC^3D). Optimal excavated scheme with relatively steeper slope angle of 47° instead of 30° was successfully implemented at the west wall on the geological section 73200 of the mine area, where the three-dimensional (3D) effect of nonlinear large deformation of the slope was taken into account. Physico-mechanical properties of the rock materials were obtained by laboratory tests conducted on samples cored from exploration drilling and rock blocks taken directly from the mine. A nonlinear Mohr–Coulomb material model with a tension cutoff was used in all present simulations. Nonlinear effect on excavated sequence was also discussed. It is demonstrated by dynamical response analysis that the action of earthquake magnitude VII (Richter) upon the relatively steeper excavated slope could not be more than that slope could bear.     

Methodology for tunnel and portal support design in mixed limestone, schist and phyllite conditions: a case study in Turkey

The purpose of this study is to present a methodology for tunnel and support design in mixed limestone, schist and phyllite conditions through investigating two highway tunnel case studies that are located along the Antalya–Alanya Highway in southern Turkey. The main lithologies of the project area are regularly jointed, recrystallized limestone and the weak lithologies of the schist unit (i.e., pelitic schist, calc schist, graphitic phyllite and alternations of these lithologies). A detailed geological and geotechnical study was carried out in the project area, and the tunnel ground support types and categories were determined according to the Q-system, rock mass rating method and New Austrian Tunneling Method (NATM). The shear strength parameters and geomechanical properties of the rock masses were obtained by using the geological strength index (GSI). The deformation moduli and post-failure behavior of the rock masses have been determined. Slope stability analyses were performed at the portal, side or cut slope sections. Kinematic and limit equilibrium analyses incorporating the effects of water pressure were performed for the regularly jointed failed rock slopes. Circular failure analogy was used for the slope stability analyses of irregularly jointed, highly foliated lithologies. Slope support system recommendations were made. A back analysis on a failed slope was performed. The results of the back analysis compared well with the results obtained through the GSI method. The tunnel grounds were divided into sections according to their rock mass classes. The deformations and stress concentrations around each tunnel section were investigated and the interactions of the empirical support systems with the rock masses were analyzed by using the Phase² finite element software. The regularly jointed rock masses were modeled to be anisotropic and the irregularly jointed, highly foliated and very deformable soil-like lithologies were modeled to be isotropic in the tunnel finite element analyses.     

Engineering geological appraisal of the Sulakyurt dam site,Turkey

This paper discusses the engineering geological investigations, diversion tunnel support design and slope stability assessment studies carried out at the Sulakyurt dam site, northeast of Ankara, Turkey. The Sulakyurt dam will be used for flood flow control and water storage for irrigation. Engineering geological mapping, discontinuity surveys, core drilling, water absorption and laboratory tests were undertaken. The RMR, Q and GSI approaches were used to estimate the rock mass quality, site characteristics, rock mass parameters and appropriate tunnel support elements. The results of kinematic and limit equilibrium analyses for the slopes on the right and left banks are reported.