Rock mass rating and Kinematic analysis for slope stability investigation of Utari dam,Lalitpur district,Uttar Pradesh

Rock mass characterization of Utari dam in Lalitpur district of Uttar Pradesh was done to identify different stability classes of rock mass. For better stability of Utari dam, foundation conditions were carefully studied by detailed field investigations of the site supplemented by laboratory tests. During feasibility and preliminary stages, rock mass characterization of slopes was conducted to identify the vulnerable zones of failure. Rock mass characterization was done by compilation of information obtained from intact rock as well as from rock mass to determine its grade and long term slope stability of the site. On the basis of Rock Mass Rating (RMR) and Geological Strength Index (GSI) slope stability is identified which lies under good quality rock mass. Kinematic analysis was conducted to find out the probability for different types of structurally controlled slope failure. Microscopic analyses were conducted to identify the degree of chemical alteration of feldspar. Clay formation by sericitization along joint planes is harmful for the stability of dam structure. Remedial measures must be taken to reduce the extent of chemical alteration. Granitoids at dam site forms a compact and stable foundation consisting of four sets of joints in which two sets were prominent which are dipping on the upstream side of the dam which reveals good condition on the dam site as leakage from reservoir will be minimum and least up-thrust on the dam structure.     

Rock mass classification and assessment of stability of critical slopes on national highway-22 in Himachal Pradesh

Rock slopes require geo-engineering evaluation to assess the instability of critical slopes leading to landslides particularly in Himalayan terrain where rocks are highly jointed, fractured and weathering prone. Interplay of discontinuities in the rocks coupled with other parameters is one of the prime causes of failure of slopes. Engineering rock mass classification, such as, rock mass rating (RMR) and slope mass rating (SMR) along with geological strength index (GSI) have widely been used for stability assessment of rock slopes above tunnel portals, and these classifications are employed here for assessment of stability of slopes of critical nature along Rampur-Powari highway in Himachal Pradesh. In the present study, out of 154 numbers of slopes, a total of 29 have been selected for assessment of their criticality by employing RMR, SMR and GSI.     

Modeling progressive failures in rock slopes with non‐persistent joints using the numerical manifold method

Rock slope failure is a complex process that usually involves both opening/sliding along pre‐existing discontinuities as well as fracturing of intact rock bridges. Discontinuity persistence is an important factor governing rock slope instabilities. However, traditional slope failure analysis assumes persistent discontinuities, and rock slope fails along a predefined persistent continuous potential failure surface because of the limitations of the analysis tools. This paper proposes the numerical manifold method (NMM) incorporated with a Mohr–Coulomb criterion‐based fracturing algorithm to simulate the progressive failure of rock slopes with non‐persistent joints. Detailed fracturing algorithm is first presented. Then, the NMM enabling fracturing is calibrated through simulating an edge‐cracked plate and the Brazilian test. Lastly, the developed code is applied to investigate the failure process of rock slopes involving non‐persistent joints. Numerical results indicate that the proposed method can capture the opening/sliding along existing discontinuities, the fracturing in intact rock bridges and the final kinematic release. Progressive slope failure is well exhibited. Copyright © 2013 John Wiley & Sons, Ltd.     

Terrestrial Photogrammetry and Numerical Modelling for the Stability Analysis of Rock Slopes in High Mountain Areas: Aiguilles Marbrées case

Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as “permafrost”, can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.     

爆破影响下岩质高边坡浅表层块体稳定性研究

摘要:岩质高边坡整体稳定性主要受软弱结构面及其组合控制,在组合有利的情况下,边坡主要发生浅表层块体失稳,开挖时的爆破振动作用是影响浅表层块体稳定的重要因素。本文以大渡河中游某岩质块状结构高边坡为例研究浅表层块体的稳定性,在总结浅表层块体失稳特征的基础上,实测爆破振动曲线,进行块体稳定性评价。研究结果表明,开挖后已失稳浅表层块体大多小于10m3,80%受软弱结构面控制,70%集中在马道下缘;实测的浅表层块体爆破振动加速度曲线显示,与邻近围岩相比,浅表层块体振动持续时间长,频率低,峰值小;等效静力法评价结果较爆破参数推算法更适用于临界失稳浅表层块体的稳定性评价。     

Rock Mass Classification and Slope Stability Assessment of Road Cut Slopes in Garhwal Himalaya, India

There are many rock mass classification schemes which are frequently used for different purposes such as estimation of strength and deformability of rock masses, stability assessment of rock slopes, tunneling and underground mining operations etc. The rock mass classification includes some inputs obtained from intact rock and discontinuity properties which have major influence on assessment of engineering behaviour of rock mass. In the present study, detail measurements were employed on road cuts slope faces in Garhwal Himalayas to collect required data to be used for rock mass classification of Rock Mass Rating (RMR) and Geological Strength Index (GSI). The stability assessment of rock slopes were also done by using Slope Mass Rating. In addition the relation between RMR and GSI were also evaluated using 50 data pairs.     

Weathering characterization for landslides modeling in granitoid rock masses of the Capo Vaticano promontory (Calabria,Italy)

This work focuses on developing multidisciplinary researches concerning weathering profiles related to landscape evolution of the Capo Vaticano promontory on the Calabria Tyrrhenian side (southern Italy). In this area, the tectonic uplift, occurred at least since Pleistocene, together with the Mediterranean climatic conditions, is the main cause of deep weathering and denudation processes. The latter occurred on the outcropping rocks of the crystalline-metamorphic basement, made up of weathered granitoids, in turn belonging to the Monte Poro granitoid complex (intermediate to felsic plutonic rocks covered by Cenozoic sedimentary successions). Field observations coupled to borehole explorations, geophysical surveys, and minero-petrographical analyses allowed the characterization of the granitoid outcrops typical of the studied area in terms of kind and degree of slope instability. This characterization was based on suitable correlations verified between several factors as weathering degree, elastic properties of rocks, and discontinuity features. Weathering profiles are mainly composed by rock masses varying from completely weathered rock with corestones of highly weathered rock (classes IV–V) to slightly weathered rocks (class II). The weathered rocks are involved in several landslide typologies such as debris flow (frequency 48.5%), translational slide (frequency 33.3%), and minor rock fall and rotational slide (frequency 9%). The achieved data allowed the establishment of a general correlation between weathering degree and type of slope instability. Debris flow-type instabilities are predominant on the steeper slopes, involving very poor rock masses ascribed to the shallowest portions of the weathering class IV. Translational slides are less widespread than the previous ones and often involve a mixture of soil and highly weathered rocks. Rotational slides are more frequently close to the top of the slopes, where the thicknesses of more weathered rocks increase, and involve mainly rock masses belonging to the weathering classes IV and V. Rock falls mostly occur on the vertical escarpments of the road cuts and are controlled by the characteristics of the main discontinuities. The assessment of rock mass rating and slope mass rating, based on the application of the discontinuity data, allowed respectively an evaluation of the quality of rock masses and of the susceptibility of rock slopes to failure. The comparison between the last one and the real stability conditions along the cut slopes shows a good correspondence. Finally, the geological strength index system was also applied for the estimation of rock mass properties. The achieved results give a worthy support for a better understanding of the relationship between the distribution of landslides and the geological features related to different weathering degrees. Therefore, they can provide a reliable tool to evaluate the potential stability conditions of the rock slopes in the studied area and a general reference framework for the study of weathering processes in other regions with similar geological features.     

Numerical Modelling of Steep Slopes in Open Rock Quarries

The key question regarding steep rock slopes along rock quarries is their stability because a rock slope failure can have critical results. In this study, the aim is to investigate the areas with potential risk for jointed karstic limestones in a rock quarry. First, to determine rock mass properties, scan-line surveys were performed, and the major orientations of discontinuities were analyzed using stereographic projection. Then, the physicomechanical properties of the slope-forming rock were determined in the laboratory, and geomechanical properties of the rock mass were determined using an empirical failure criterion. Finally, the quarry slope stability was assessed in accordance with numerical modelling. According to the results obtained, the numerical modelling of steep rock slopes can be efficiently evaluated by using finite element method. Beside this, the presence of joints intersecting the main discontinuity sets, the filling materials of discontinuities resulting from weathering of limestone and surface deposits, surcharge load due to mine waste dumped on the slopes and excavation blasting during construction of quarry area play a key role when modelling the steep rock slopes by using finite element method.     

露天煤矿冻结岩土边坡介质特征与稳定性分析

为了科学评价冻岩露天矿边坡稳定性,并采用有效措施保证冻岩边坡工程的安全建设和运营,分析了岩石在不同温度条件下多个物理力学参数的变化规律,结果表明,冻结态使岩石的强度得到一定的提高,而冻融循环使岩石的强度产生一定的削弱。由于岩体具有介质和结构的双重属性,冻融循环作用对岩体的介质和结构面损伤均较显著,可以通过改进的Hoek-Brown岩体强度准则分析冻融环境中的岩体强度。基于木里聚乎更矿区冻岩露天煤矿边坡的调查分析,总结归纳了该区冻岩边坡的破坏现象和类型,在冻融循环作用下冻岩边坡的破坏模式基本为浅表部的渐进式破坏。      

Rock Slope Stability Assessment Using Geomechanical Classification and its Application for Specific Slopes along Kodaikkanal-Palani Hill Road,Western Ghats,India

Linear infrastructure networks like roads play a vital role in the socio-economic development of hill towns centered on tourism. Stability of the slopes along the hill roads are therefore a major concern and slope failures lead to disruption of traffic and loss of property/life or both. This study analyses the stability of cut-slopes along the Kodaikkanal – Palani hill road in the Western Ghats, India using rock mass classification systems like rock mass rating (RMR), slope mass rating (SMR) and continuous slope mass rating (CSMR). These geomechanical classifications provide a preliminary assessment of rock quality based on rock strength, discontinuity properties, hydrogeological condition of the slopes and slope stability based on the inherent rock strength parameters, discontinuity orientation and method of excavation. The results showed that both rock quality and discontinuity orientation contribute to type of failure in rock slopes with RMR > 40. SMR results are conservative while CSMR classification is matches more closely to the failures obtained from the field survey. CSMR classification represents continuous slope stability conditions and hence are more suitable for development of spatial database. Cutting of roads, thereby, steepening slopes has a definite influence on the stability of slopes.     

水力作用下岩质斜坡破坏机制和稳定性分析研究现状

基于国内外研究现状和岩质滑坡案例,总结出岩质滑坡的水力致灾机制,归纳考虑水力作用下的岩质斜坡主要失稳破坏模式,评述了岩质斜坡稳定性分析方法。岩质滑坡的水力致灾机制主要由于水对滑体产生的静水压力（岩体侧面的推力、滑面的扬压力和岩体的浮力）和动水压力（向坡外的渗透力）作用。从渗流—应力耦合的角度可较全面评价水渗流对坡体稳定性的影响。斜坡的岩体结构决定了水力作用方式和坡体的失稳破坏形式,考虑水力作用下的岩质斜坡失稳破坏形式主要有:顺层滑动、平推式滑动、楔形体滑移和危岩的崩塌。对于水力作用下岩质斜坡的稳定性分析方法主要有极限平衡法、有限元强度折减法、基于断裂力学的危岩稳定性分析法和渗流—应力耦合模型分析法,其中前两种方法应用较为广泛。      

坡后土体推力作用下反倾节理岩质边坡次生倾倒机理分析

次生倾倒破坏是层状反倾岩质边坡的一种主要破坏模式,极限平衡理论是分析倾倒破坏的常用方法,研究反倾节理岩质边坡次生倾倒破坏机理对边坡工程众多的西南山区基础设施建设具有重要的工程指导意义。在Goodman和Bray块体倾倒破坏极限平衡分析方法的基础上,建立了考虑地下水压力、节理连通率、岩体黏聚力等影响因素的反倾岩质边坡在坡后土体推力作用下的次生倾倒地质力学模型,提出了坡后土体推力作用下的反倾节理岩质边坡次生倾倒破坏的解析分析方法,推导出了边坡各岩层下推力的解析表达式,提出了边坡倾倒破坏的综合安全系数,并编写了对应的matlab计算程序,为该类边坡的设计和加固提供了理论依据。通过算例分析表明,与单纯岩质边坡块体倾倒破坏相比,该类边坡次生倾倒破坏形式的特点是破坏基准面以上岩层自上而下依次分为滑移区、倾倒区和稳定区3个部分;地下水压力、节理连通率、底裂面岩体黏聚力对各岩层的破坏形式、稳定安全系数大小都具有明显影响,尤其是在坡体中下部及坡脚部分最为敏感;而各岩层稳定安全系数最小的区域集中于边坡中上部。     

基于岩体结构特征和未确知测度评价模型的岩质开挖边坡稳定性研究

综合黔西地区层状岩质开挖边坡研究成果发现:岩体结构特征是分析评价层状边坡变形失稳模式、机制和稳定性的重要基础。因此,结合该地区层状边坡地质条件的差异性,针对性地划分岩体结构类型对边坡的分析评价尤为重要。考虑地层岩性组合、地质构造、软弱夹层（结构面）因素,系统地将边坡岩体结构类型分为4个大类（近水平-缓倾边坡岩体,倾斜层状边坡岩体,陡倾、直立、倒转层状岩体,地质构造作用强烈或含有溶蚀洞穴、沟壑的边坡岩体）和10个亚类,并针对相应类型的边坡进行工程地质综合评价,分别阐述了失稳模式和机制。以边坡岩体结构类型为基础,甄选影响开挖边坡稳定性的6个定性指标和6个定量指标;对指标组合赋权,用未确知测度理论对边坡进行稳定性预测评价,建立了“岩体结构-指标组合赋权-未确知测度理论”的新评价体系。实例预测结果表明预测结果与实际情况具有较好的一致性,说明该方法是一种可靠性高、科学合理的稳定性预测新方法,可在相关工程领域中应用推广。     

Effect of rock mass disturbance on the stability of rock slopes using the Hoek–Brown failure criterion

The process of creating man made or “cut” slopes in rock invariably leads to stress relief within the rock mass which in turn induces a certain degree of fracturing and disturbance. The level of disturbance can be particularly significant when the slope is formed using blasting techniques. However, the effects of this disturbance on the overall rock slope stability have not been investigated thoroughly in the current literature. In order to account for rock mass disturbance during construction, a disturbance factor has been included in the Hoek–Brown failure criterion [1]. This paper uses finite element upper and lower bound limit analyses to estimate rock slope stability based on the Hoek–Brown failure criterion whilst including the effect of rock mass disturbance. A rigorous set of analyses have been performed where the level of disturbance is considered as constant or linearly varying throughout the slope. The results are then compared to a number of reported case histories for verification purposes. From the results of this study, the disturbance factor was found to have significant influence on the rock slope stability assessment, especially for poorer quality rock masses. Hence, cautious engineering judgement must be exercised when estimating the level of disturbance. In addition, utilising stability charts to estimate the stability of cut rock slopes without considering the rock mass disturbance may lead to significant overestimations.     

Qualitative stability assessment of cut slopes along the National Highway-05 around Jhakri area,Himachal Pradesh,India

Several deformation phases in tectonically active Himalayas have rendered the rock masses very complex in terms of structure, lithology and degree of metamorphism. Again, anthropogenic activities such as roads, tunnels and other civil engineering constructions have led to a state of disequilibrium which in many cases, results in failure of rock masses. National Highway-05 around Jhakri area in India is a major connecting route to the China border in the hilly terrains of the state Himachal Pradesh. It cuts through the Himalayan rocks and has a hazardous history of landslides destroying human lives and interrupting communication very frequently. As a contribution towards the mitigation process, a study has been carried out along the highway to analyse kinematic stability and qualitative estimation of rock mass condition through rock mass classification systems. The kinematic analysis shows that the rock slopes are prone to planar and wedge failure. Rock mass rating for most of the locations lies between 7 and 34, representing a poor rock mass quality (Class IV), whereas slope mass rating is more disperse and ranges from 11 to 52 for most of the slopes (Class III, IV and V).     

Pseudo-dynamic stability of rock slope considering Hoek–Brown strength criterion

Rock slopes with planar joints or weak structural planes are vulnerable in nature, especially suffering from the natural hazards, instabilities of slopes are more prone to occur. Therefore, concerning to the influence of earthquakes, this paper performs a new procedure to evaluate slope stability in a geomaterial governed by Hoek–Brown strength criterion. A rotational failure mechanism determined by 21 dependent angle variables is introduced to respect the Hoek–Brown strength criterion. The earthquake load is characterized by a modified pseudo-dynamic method that does not violate the zero boundary condition and considers the damping properties of geomaterials. A slice approach is adopted to calculate the earthquake-induced inertial force work rate. The stability number of rock slope is considered to measure the safety. The stability number is formulated as a classical optimization problem controlled by 21 dependent angle variables and a time variable which need to be optimized by the genetic algorithm toolbox. Comparisons with the literature are made to prove rationality and accuracy of the proposed procedure. Parametric study is carried out to reveal the influence of dynamic properties. For engineering application, stability charts are provided for a quick assessment of slope safety.

     

基于Hoek-Brown准则的非等比强度折减方法

针对节理岩质边坡稳定性分析问题,开展了基于Hoek-Brown破坏准则的强度折减法研究。边坡的失稳过程是一个渐进累积破坏过程,破坏过程中各强度参数的衰减程度不同,在强度折减法中对应的折减系数也不同,不同折减系数间关系的确定及其综合安全系数的定义值得深入探讨。首先从岩体材料软化（硬化）特性出发,根据岩体强度参数从峰值强度到残余强度的变化规律,推导了Hoek-Brown破坏准则中3个强度参数折减系数间的数学关系式,然后以折减前后滑面上抗滑力之比定义综合安全系数来评价边坡的稳定性,最后结合算例验证了该方法的合理性,可有效应用于节理岩体边坡的稳定性分析。     

双临空面岩质边坡滑动与倾倒破坏的运动学分析

临空面的几何形状在边坡破坏模式与稳定性分析中起着举足轻重的作用。运动学分析是确定边坡破坏模式与评价边坡稳定性的一种有效方法。目前基于运动学分析的边坡稳定性研究主要集中于单临空面边坡的破坏模式与最大安全开挖边坡角的确定。本文将此项研究扩展至双临空面边坡,将其破坏模式细分为4种,分别为沿结构面发生单平面滑动、沿结构面发生楔形体滑动、沿两个结构面的交线发生楔形体滑动以及倾倒破坏。在立体投影中得出,平滑滑动与楔形体滑动的滑动区为双临空面真倾向线与摩擦圆所组成的区域,单个结构面倾角矢量与两个结构面交线矢量位于该区城内;倾倒破坏区为双临空面真倾向线、摩擦圆与基圆所组成的区域,结构面的法向矢量位于该区城内。提出了双临空面边坡最大安全开挖边坡角的确定方法及边坡设计原则。最后将上述方法应用于三峡库区湖北省秭归县郭家坝镇郭家坝村生基坡高边坡,研究了该双临空面边坡的破坏模式并给出了最大安全边坡角的建议值     

汶川地震极重灾区地质背景及次生斜坡灾害空间发育规律

512汶川大地震造成大量的次生斜坡灾害,本次研究区域为汶川大地震的11个重灾区,包括汶川、北川、青川、安县、平武、茂县、江油、彭州、什邡、绵竹、理县等市县。通过对重灾区航片、卫片、雷达图像的解译研究发现,重灾区次生斜坡灾害的主要灾种表现为崩塌、滑坡以及崩塌、滑坡高速运动解体形成的碎屑流（个别地方由于水的参与表现为泥石流）以及它们堵江形成的堰塞湖。研究发现地震次生斜坡灾害的发育具有明显的丛集性规律。从区域上看,次生斜坡灾害明显呈带状,沿龙门山断裂带展布,并主要受北川映秀断裂控制。各灾种的发育在不同地段发育的规模、频率差别较大。以灾害分布面积来排序,汶川县灾害面积最大,为131.55km2,其次为北川县,为45.57km2,其余9个县（市）灾害面积相差不大,均介于6~17km2,其中理县灾害面积最小,为6.25km2。各灾种的发育在不同地段发育的规模、频率差别较大。青川县、平武县灾种主要为滑坡,汶川县、茂县、安县、理县灾种主要表现崩塌转化的碎屑流,北川的主要灾种则为碎屑流,其次为滑坡,什邡、彭州、绵竹、江油等地主要灾种为崩塌。 灾种发育的这种地域性差别主要受控于地层岩性,除此而外,还与构造特征、地形地貌等因素紧密相关。研究表明:岩性对灾害种类的展布有决定性控制作用。统计发现,岩性越坚硬,崩塌、碎屑流发育率越高,滑坡则在软岩地区、较软岩地区和较坚硬区发育率最高,泥石流则在软岩地区最为发育。地形地貌对次生斜坡灾害的发育有重要影响,统计表明,崩塌、碎屑流以及泥石流在1200～2000m坡段范围内发育率最高,其次为800～1200m坡段;而滑坡则在800～1200m坡段范围发育率最高。对坡度而言,除11~20坡度范围外,崩塌和碎屑流的发育率总体具有随坡度增高而增大的特点;而滑坡和泥石流的发育率呈现典型的单峰特征,在1~20范围内发育率最大。坡向对地震次生斜坡灾害的发育影响不明显。 地震次生斜坡灾害的发育规律表明,地震斜坡灾害的发生主要受控于活动构造本身,并沿活动构造呈带状展布,同时受场地条件如岩性、地形地貌等因素的强烈控制。     

A resilience framework for safety management of fossil fuel power plant

In the present study, cut slope stability assessment along ghat road section of Kolli hills was carried out by using various geotechnical parameters of rock and soil slope sections and structural kinematics of major discontinuities is presented. The rock slope (RS) stability assessment was carried out using Rock Mass Rating basic (RMR_basic) and Slope Mass Rating (SMR) classification systems. The type of failure and their Factor of Safety (FOS) for individual RS was calculated using Hoek and Bray method. In the case of soil slopes (SS), the FOS was calculated using Circular Failure Chart (CFC) and Limit Equilibrium (LE) methods. The input data for the slope stability analyses were collected through extensive field work followed by stereonet plotting and laboratory test. There are six rock slope sections, and five soil slope sections were taken into consideration for the cut slope stability analyses. The area depicts class II (RS-1, 2, & 6) and class III (RS-3, 4, & 5) of RMR classes. The SMR result depicts for RS-1, RS-2, and RS-6 are 64.40, 60.02, and 60.70, respectively, and falls in class II stable condition. The SMR values of RS-3 and RS-5 were 44.33 and 57, respectively, and come under the class III partially stable condition. The RS-4 with SMR value of 17.33 falls under the class I completely unstable condition. The FOS of planar failure case indicates that RS-3 (FOS = 0.22) is more unstable, while all other sections are having greater than 1 FOS. The calculated FOS values using CFC method reveals that the FOS is very close to 1 for all the SS sections that fall under completely saturated condition which indicates that these slope sections may fail during heavy rainfall. In LE method, the sections SS-3 and SS-4 are unsafe under partially and completely saturated (natural slope) condition. In average slope condition, all the SS sections are unsafe under partially or completely saturated conditions. The facets 2, 3, 4, and 5 required mitigation measures, to improve the stability of slopes. Site-specific mitigation measures were suggested for partially or completely unstable rock and soil cut slopes.