Cut Slope Design Recommendations for Sub-Horizontal Hard Sedimentary Rock Units in Ohio, USA

Although most cut slopes in Ohio consist of inter-layered, sub-horizontal units of hard and soft sedimentary rocks (sandstone, limestone, dolostone, shale, claystone, mudstone), slopes consisting of relatively thick hard rock units are not uncommon. Design of stable cut slopes in hard rock units needs to consider rock mass strength and orientation of discontinuities with respect to slope face. Results of kinematic stability analyses show that hard-rock cut slopes are less likely to have conventional plane and wedge failures, caused by unfavorable orientation of discontinuities. The main cause of failure is identified to be the undercutting-induced toppling, which is not amenable to traditional kinematic or rock mass strength-based analyses. Therefore, to recommend a suitable slope angle, numerical models, using UDEC software, were employed to study how various slope angles affect the process of undercutting-induced toppling failures. The UDEC models showed a slope angle of 45° (1H:1 V) to be the most stable angle. However, a 63° (0.5H:1 V) slope angle can significantly reduce the potential for such failures and is therefore more appropriate than the widely used angle of 76° (0.25H:1 V).     

A new slope mass rating in mountainous terrain, Jammu and Kashmir Himalayas: application of geophysical technique in slope stability studies

The slopes of western Lesser Himalaya (at Sangaldhan Block of Udhampur near Ramban, Jammu and Kashmir India) are being severely affected by tectonic and erosional activities. These activities result in deposit of a thick cover of rock fragments and overburden just above the hard rock. The thickness of overburden cover has directly affected the stability of slope in the study area, though the traditional stability estimation techniques, rock mass rating and slope mass rating, rate this area as moderately stable which does not represent the real stability condition. In this research work, the geotechnical and geophysical surveys have been carried out to reckon the slope stability conditions more accurately as compared to traditional slope stability estimation techniques. A new rating, new slope mass rating, is developed, which gives a better picture of the stability of slopes. It incorporates a new parameter of overburden thickness profile, along with slope angle and other associated factors on the slopes of the mountainous terrains. The vertical electrical sounding surveys were conducted for the demarcation of rock–overburden interface and for determining the overburden cover. This new classification depicts an increase of 12.84 % in unstable slope areas giving a better assessment and factual picture of slope stability in our study area. This study also enumerates the importance of geophysical applications in slope stability studies. The research work is applicable in mountainous terrains such as Himalaya, and the major component of the application is the orientation of overburden or the profile of thickness in relation with slope of surface.     

论水电工程边坡分类

相对其他工程而言,水电工程边坡规模大,所处的地质环境条件更加复杂。随着我国水电工程的大开发,在高山峡谷中修建了不少高坝,边坡开挖高达300m以上,而且在开口线之上还可能存在数百米甚至千米以上的自然边坡,坡度陡峻,高边坡的稳定性问题已经成为工程建设中的关键技术问题。为揭示边坡特征,方便描述、交流和评价,进行科学的边坡分类就具有重要的理论和现实意义。在收集分析国内外边坡分类体系的基础上,笔者结合多年来的工程实践认为,已有的边坡分类方法不能完全适应水电工程边坡状况,有必要进行改进与完善。根据针对性、体现本质、层次性和系统性等4个原则,本文提出了水电工程边坡分类框架:第1层次按边坡与所在工程位置关系划分; 第二层次按边坡重要性和危害性进行边坡分级; 第三层次按边坡特征、几何特征和变形破坏特征进行分类; 在第四层次分类中,再依据其物质组成、坡体结构、坡度、高度、变形机制、破坏形式、变形范围和边坡的危险源分别进行了进一步的分类。文中首次提出了边坡分级表、峻坡与悬坡、高边坡与超高边坡的分界线、以及环境边坡按危险源的分类方法。建议峻坡与悬坡的分界为60,高边坡与超高边坡分界为80m,300m的边坡为特高边坡,并指出采用坡体结构进行分类,能揭示边坡可能变形破坏的边界条件和失稳模式,其工程应用性更强。     

基于有限元强度折减法的单双面边坡稳定性分析

利用强度折减法和有限元分析软件ABAQUS，研究了单面和双面土体边坡的稳定性。首先，利用典型算例验证了所采用方法的可行性，然后通过模型数值模拟，分析了不同的坡体参数，如坡角、坡高、黏聚力和内摩擦角等情况下单面和双面边坡的稳定性。探讨了各参数对单面和双面边坡稳定安全系数的影响特征和规律，同时也展现了土体塑性应变区发生和扩展过程。结果表明:(1)坡角、坡高、黏聚力和内摩擦角等参数的单独变化对边坡安全性系数的影响规律基本一致、近似线性变化，对单面和双面边坡稳定性的影响规律相同；(2)双面边坡稳定性比单面边坡的有所降低，但边坡几何和物理参数取一定范围内的值时，两种趋于一致；(3)坡面顶部的位移拐点和坡体塑性应变区贯通之间并不是同时出现，土体边坡稳定性评价的不同判别准则之间存在差异。建议实际工程中边坡稳定性评价考虑采用双面边坡甚至更复杂边坡分析模型，同时需综合利用边坡稳定临界状态的不同判别准则。     

荔湾3-1气田管线路由海底峡谷段斜坡稳定性分析

针对南海荔湾3-1气田管线穿过的海底峡谷区6个典型斜坡剖面,分别采用有限元强度折减法和极限平衡法开展斜坡稳定性分析,模型考虑了土层强度随深度的变化。计算结果对比表明,有限元强度折减法与极限平衡法分析结果一致,其中与Spencer法结果最接近,稳定系数相对误差小于3.5%。重力作用下各斜坡基本处于相对稳定状态,峡谷中下部土强度较低且坡度较高的局部区域接近临界状态,峡谷头部因坡度相对较小且土体强度相对较大,其斜坡稳定系数相对较高。地震水平加速度能够明显降低该区斜坡的稳定系数,且随着加速度值的增大滑动深度逐渐变大。当水平加速度达到0.2g时峡谷中下部区域大部分会发生滑动。海底地形坡度和土层强度是影响峡谷区斜坡稳定性的主要因素,且稳定系数与滑动面对局部坡度和强度分布较为敏感,合理的稳定性评价依赖于精确的地形数据与土层力学参数。     

Prediction of slope stability using multiple linear regression (MLR) and artificial neural network (ANN)

The stability problem of natural slopes, filled slopes, and cut slopes are commonly encountered in Civil Engineering Projects. Predicting the slope stability is an everyday task for geotechnical engineers. In this paper, a study has been done to predict the factor of safety (FOS) of the slopes using multiple linear regression (MLR) and artificial neural network (ANN). A total of 200 cases with different geometric and shear strength parameters were analyzed by using the well-known slope stability methods like Fellenius method, Bishop’s method, Janbu method, and Morgenstern and Price method. The FOS values obtained by these slope stability methods were used to develop the prediction models using MLR and ANN. Further, a few case studies have been done along the Jorabat-Shillong Expressway (NH-40) in India, using the finite element method (FEM). The output values of FEM were compared with the developed prediction models to find the best prediction model and the results were discussed.     

Topographical features of rainfall-triggered landslides in Mon State,Myanmar, August 2019: spatial distribution heterogeneity and uncommon large relative heights

Continuous 5-day (August 4–9, 2019) torrential rainfall in the monsoon season triggered more than 90 landslides on northwest-southeast extended mountain range of Mon State, Myanmar. In this study, remote sensing images, DEM, and limited fieldworks were used to create the landslide inventory. The topography features of these landslides are analyzed via ArcGIS. The largest one occurred on 9 August 2019 and caused 75 deaths and 27 buildings were damaged. This landslide occurred on gentle topography (slope angle, 23°) with long run-out, in which the angle of reach was relatively low (10°). The volume was 111,878 m³ was mainly composed of weathered granite and red soil and the sliding depth was approximately 7.5 m. Topographic characteristics including the relative slope height, angle of reach, and slope angle of source area of 35 landslides with areas?>?4000 m² were analyzed. The spatial distribution characteristics and topographic features of the 35 landslides below are distinguished: (1) the concentration of most of landslides on southwest-facing slopes showing the heterogeneous spatial distribution of landslide; (2) an uncommon landslide distribution in which more than half of landslide originates from upper slope; (3) the range of the angle of the source area (17°–38°) compatible with the internal friction angle of soils in tropical regions (17°–33°); and (4) the tangent of the angle of reach is generally smaller than 0.5 (angle of reach?<?27°) shows a relative high mobility and the relation between landslide mobility and the slope angle of the landslide source area is similar to the one of earthquake-triggered landslides, even though the triggering mechanism, landslide type, and landslide volume are dramatically different.

     

坡积松散体稳定性模型试验研究

云南西北部三江源高海拔、高深切地区,坡积松散体稳定性是公路边坡面临的主要问题之一,模型试验是研究松散体稳定性各影响因素最有效的手段。根据相似原理,设计模型试验的主要几何相似常数,采用一系列手段改造模型试验材料,使其达到材料强度、重度相似。一系列模型破坏条件真实再现现场坡积松散体的滑坡条件,试验结果分析对相关设计、施工和科研人员有较好的借鉴作用。模型试验材料从松散状态到较密实状态,开始破坏的自然坡角提高42%～100%,c值提高约50%～120%, 值提高约6%～8%,密实状态提高,坡体的强度提高,相应坡体的稳定性提高,起始破坏的自然坡角也显著提高;降雨使坡体含水率提高近饱和时,充分软化的c值下降约70%, 值下降约7%,表明雨水下渗软化是导致坡积松散体产生滑动的最根本、最直接的因素。模拟降雨的土体强度变化过程对松散体边坡稳定性研究有较好的参考价值。     

Coupled transient saturated–unsaturated seepage and limit equilibrium analysis for slopes: influence of rapid water level changes

This study investigates the influence of the water level fluctuation on the stability of soil slopes using coupled seepage and slope stability analysis. A simulation framework was proposed and implemented seamlessly using Python code to seek insights into three factors that have not been thoroughly studied for this issue: soil unit weight variation in the unsaturated zone, unsaturated shear strength models, and velocity of water drawdown. For this purpose, the seepage analysis was carried out by discretizing a numerical seepage analysis model using a finite element analysis platform, FEniCS. The output of the seepage analysis, i.e., pore water pressure distribution, was used as input for the slope stability analysis. Limit equilibrium methods including the Bishop Simplified method and the Ordinary Method of Slices were modified to take into consideration the unsaturated shear strength, unit weight variation in the unsaturated zone, and hydrostatic pressure changes in response to the water level fluctuation of a reservoir. Both seepage and slope analysis modules were validated against commercial programs. Analysis results obtained with the validated framework clearly revealed the distinct influences of the three factors in representative silty and sandy slopes.

     

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.

     

预应力锚索加固土质边坡极限平衡稳定性分析

基于滑动面搜索新方法,对预应力锚索加固边坡进行稳定性分析。通过将锚索的加固效应简化为作用在土条(柱)底面上的一个外力,实现了条分(柱)法下二维和三维锚索加固边坡的安全系数计算。经过算例对比分析,验证了本文方法的可行性,然后,在一定程度上研究了锚索倾角、三维滑动体长度L、锚索锚固力F以及水平加固间距S变化时对边坡稳定性的影响。研究结果表明:(1)锚索加固可有效提高边坡的稳定性,同时,也增大了原有边坡发生滑动的范围; (2)随着三维滑动体长度L的增大,三维边坡(包括未加固和锚索加固)的稳定性趋于二维边坡稳定性; (3)单位水平加固间距上的锚固力越大,锚索对边坡的加固效应越明显。     

Geometric model for toppling-prone deformation of layered reverse-dip slope

This paper presents the analyses of toppling response of layered reverse-dip slopes under the influence of geometric factors of slope angle, strata thickness and dip. The toppling response of reverse-dip slopes under different geometric factors is obtained by using the discrete element code UDEC. Then, a prediction model for toppling deformation is developed by utilizing support vector machine and the toppling-prone combinations of these geometric factors are determined from a total of 120 samples of reverse-dip slopes. The study has shown that the geometric model is a quarter of a spheroid with a slope angle of 80°, a strata dip of 80°, and a strata thickness of 0.19 m as the center. The length of the long equatorial radius of the spheroid is 31° (strata dip axial), that of the short equatorial radius is 21° (slope angle axial), and the polar radius is 0.075 m (strata thickness axial). And the ratio of long equatorial radius, short equatorial radius, and polar radius is 2.48:1.68:1.00.

     

Stability assessment of slide zones in Lesser Himalayan part of Yamunotri pilgrimage route,Uttarakhand, India

The present study deals with the slope stability analysis and geotechnical assessment of a part of pilgrimage route to one of the holy shrines of India, i.e. Yamunotri. The route also embraces a proposed site for 204 m high concrete gravity dam across River Yamuna near Lakhwar village with the aim of generation of 300 MW power. Several slide zones were identified and based on the discontinuity orientation, structural features and debris materials, they are recognised as planar, wedge or circular failure types. The morphological dimensions, structural data, orientations and geotechnical parameters of circular failure slides within weathered quartzites, phyllites and shales were evaluated by extensive field work and by laboratory tests for their stability analysis. Internal mechanisms, cohesion and angle of internal friction that resist shear stress in slope materials, obtained from direct shear test are showing minor variation due to relatively consistent grain size distribution and mineralogical composition. General slope is about 40°–43° with sparse vegetation. Materials in and around slide zones are sands with appreciable amount of fines falling in SP–SM category as per Unified Soil Classification System (USCS), except Niste B slide which has clean sands lying in SP group. Factor of safety, computed by requisite parameters of strength, soil and slope properties in circular failure charts, varies from 1.02 to 1.23 in dry conditions while it reduces below unity with increasing saturation, representing stable conditions in dry conditions but with seepage and saturation along the cracks and discontinuities during rainfall make them unstable. Presence of steep slopes, proximity to stream channels and significant weathered and jointed area are causative factors in the route with rainfall and road widening as major triggers initiating the failure.     

基于间接边界元方法的SH波倾斜入射下边坡动力响应特征

地震作用下山体边坡的动力响应规律与地震波入射角度显著相关,本文基于间接边界元方法研究SH波倾斜入射下边坡的动力响应特征.基于间接边界元理论研发了用于边坡岩体动力响应分析的边界元程序,通过计算平直裂隙对弹性波的反射及散射波波场对程序进行验证,并详细探讨了不同类型的边坡在各种入射角度的应力波作用下的响应特性.SH波铅直向入射时,半圆形凹陷地形的谷肩位置地震动振幅最小,而半圆形凸起地形的最高点位置振幅最大,单面坡的坡肩位置地震动最大,楔形凸起地形的坡顶地震动最强烈;当SH波入射角增大,各类边坡的最大地震动力响应位置也有所偏移,地震放大系数亦随之变化;以樟木镇边坡为实例揭示了复杂形态边坡岩体中的局部凸起对地震动的放大作用.研究结果表明,边坡微地形特征对地震动力响应影响非常大,凸起山体坡顶的动力放大效应最为显著;同一边坡在不同入射角地震波作用下产生的动力放大系数以及发生的位置不同.本文的研究结果对评价坡体稳定性和边坡工程抗震防设等具有重要的指导意义.      

地震条件下不同类型边坡的稳定性研究

用sarma法计算了不同坡高、不同坡角、不同岩体和结构面力学参数的边坡在不同水平地震加速度系数下对应的安全系数,建立了一套能方便快捷地查询边坡安全系数的系统,为各种类型边坡的稳定性评价提供了依据。此外,还分析了坡高、坡角、地震加速度系数、岩体和结构面力学参数对地震边坡安全系数的影响。通过对比查询系统得到的安全系数与其他已有的地震边坡稳定性评价方法得到的安全系数的差异,得出用这种新安全系数查询方法得到的安全系数与其他安全系数计算方法得出的安全系数相差不大。通过将这种新的地震边坡稳定性评价方法应用到几个实际边坡中,所得到的评价结果与滑坡的实际发生情况一致。     

基于变形分区确定某反倾岩质岸坡变形体锁固段

对处于蠕滑阶段的边坡而言,准确确定蠕滑段和锁固段是进行稳定性评价及演化趋势预测的基础和前提。以我国西南山区某水库型岸坡变形体为例,在综合分析岸坡工程地质条件的基础上,通过联合运用野外现场地质调查、地表位移监测、钻孔、平硐、深部位移监测、物探等多种勘察手段,查明了岸坡的结构特征,并分别对岸坡进行地表和深部变形分区。 在此基础上,结合当前稳定性现状,划分出岸坡蠕滑段与锁固段。结果表明:(1)岸坡在河谷下切过程中发生了弯曲倾倒变形,弯曲折断面深度为20～80m;(2)岸坡前部为蠕滑段,中部为锁固段,后部为拉裂段,具备滑移-拉裂-剪断三段式发育特征。研究结果可直接用于该岸坡变形体的稳定性评价,且对于同类型处于蠕滑阶段边坡的勘察手段及综合分析具有一定的借鉴意义。     

A new rating system approach for risk analysis of rock slopes

In this paper, an approach is presented to analyze the stability risk of rock slopes based on a new rating system. Three factors are used to estimate the risk level of rock slopes: (1) failure probability, (2) element at risk rating, and (3) vulnerability rating. Element at risk and vulnerability ratings are both given a range from 0 to 10, and the probability of failure is varied between 0 and 1, so the risk rating ranges between 0 and 100. This risk rating can be used to determine both the quantitative and qualitative risk levels of slopes at the same time. The method is tested on the western sector of the slopes facing Songun copper plant phase III, Iran, to clarify its procedures and assess its validity. Deterministic kinematic analyses showed that the slope has a potential for circular failure. Risk assessments revealed that the risk levels of the slope in both static and pseudo-static conditions are “very low” and “high,” respectively.

     

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.     

北京市门头沟区某公路岩质边坡稳定性分级研究

北京市门头沟区某公路岩质边坡数量多,边坡物理力学性质及其影响因素复杂多变,无法获取每个边坡岩体的物理力学参数,因此,对大量边坡进行力学稳定性分析十分困难。采用层次分析和模糊综合评价方法,根据各种因素对岩质边坡稳定性影响的定性分析,确定了2级4类共9个边坡稳定性影响因子,将边坡的稳定性级别划分为4级,即稳定、基本稳定、较不稳定和不稳定; 然后,构建了隶属度矩阵和权重矩阵; 最后,对每个边坡的稳定性进行模糊综合评价。分析结果表明,在所研究的113个边坡中,不稳定边坡3个,占总边坡的3%,较不稳定边坡27个,占24%,基本稳定边坡52个,占46%,稳定边坡31个,占27%。因此认为: 当边坡数量众多、边界条件模糊、影响因素复杂时,模糊综合评判是比较合适的边坡稳定性分析方法; 应用最大隶属度原则时,需根据各种因素对边坡稳定性影响的因果关系,对最大隶属度原则的有效性进行评估,以防出现评判失效。     

含软弱夹层岩质边坡稳定性研究现状及发展趋势

含软弱夹层岩质边坡在自然环境和工程实践中都比较常见，稳定性差，边坡失稳产生了大量的滑坡灾害，造成大量人员伤亡和经济损失。因此，含软弱夹层岩质边坡稳定性研究一直是工程地质和岩土工程领域的研究重点之一。在收集整理国内外相关资料的基础上，从自重工况、开挖工况、暴雨和蓄水工况、地震工况方面总结了目前含软弱夹层岩质边坡稳定性的研究现状及进展，取得如下主要认识:(1)软弱夹层对岩质边坡稳定性有显著不利影响，含软弱夹层岩质边坡的稳定性比均质岩质边坡、不含软弱夹层的层状岩质边坡都差；(2)含软弱夹层岩质边坡的稳定性系数、变形特征和破坏模式与软弱夹层的含水状态、抗剪强度、倾角、厚度、间距、层数和边坡坡度有关；(3)开挖容易诱发坡体沿软弱夹层滑坡，含软弱夹层岩质边坡开挖后需要及时支护；(4)爆破层裂效应改变了软弱夹层与围岩的接触状态，减小了它们之间的凝聚力和摩擦力，导致边坡稳定性降低；(5)暴雨和蓄水都不利于含软弱夹层岩质边坡稳定；(6)岩质边坡地震动力响应和变形破坏特征受软弱夹层参数(厚度、倾角、含水状态)、地震波特性(地震波的类型、幅值、频率、激振方向)和边坡结构(顺层或反倾)共同影响；(7)在软弱夹层对水平向动力响应的放大或减弱作用及厚层软弱夹层的消能减震作用方面仍然存在不同观点。在此基础上，分析了研究方法的优缺点，指出当前含软弱夹层岩质边坡稳定性研究存在的问题。最后，针对该领域的研究现状，提出了未来的研究重点和方向，主要包括:含多层软弱夹层岩质边坡的渐进性变形破坏过程和稳定性；全面深入研究单因素作用(开挖卸荷、爆破、地震、暴雨、库水位变化、地下水等)对含软弱夹层岩质边坡稳定性的影响机制；多因素耦合作用下含软弱夹层岩质边坡稳定性；支挡结构体系对含多层软弱夹层高陡岩质边坡的加固机制。