Time evolution and spatial accumulation of progressive failure for Xinhua slope in the Dagangshan reservoir,Southwest China

This paper presents a preliminary study of time evolution and spatial accumulation of progressive failure for ancient landslide deposits in Xinhua slope. According to the geological response after impoundment, the Xinhua slope has shown the spatial accumulation of deformation, such as ground cracks in the rear edge, toe collapse, local shallow slides in intense rainfall, and progressive creep displacement. Approximately 2 years of monitoring was performed for the Xinhua slope with the assistance of the global navigation satellite system (GNSS), unmanned aerial vehicles (UAVs), and field investigations. The deformation process of a reservoir landslide is considered to be a comprehensive and complicated combination of geological influence from various adverse factors. Field investigations and monitoring indicate that the major serious influence after completion of dam construction comes from the initial large-scale impoundment, the fluctuation of water level, and the existence of a flood season. The creep/slip deformation of slope deposits is a result of integration with adverse hydraulic conditions, e.g., strong rainfall, intense currents and transient seepage flow inside the slope deposits, and activation by water level fluctuation, which can be verified from the twofold evident deformation in the flood season. For the reservoir with daily regulation ability, the occurrence of evident deformations in July highlights that the regulation plan for water level in the flood season is important for controlling the deformation of slope deposits, where the fluctuation of the water level is no more than 10 m in the operation period.     

Investigating a reservoir bank slope displacement history with multi-frequency satellite SAR data

Slope instability arisen along with dam construction is a common problem of great concern in reservoir areas. Thus, displacement monitoring of active slopes is of great importance for the safety of dam operation. The unstable Guobu slope is located only about 1.5 km away from Laxiwa hydropower station in upstream Yellow River. In this study, Synthetic Aperture Radar (SAR) datasets acquired by C-band Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR), L-band Advanced Land Observing Satellite 2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR-2), and X-band TerraSAR-X covering different evolution stages of Guobu slope were collected to investigate the displacement history so as to facilitate understanding of its deformation and failure mechanisms. The displacements occurred during the past decade were quantitatively identified for the first time by SAR pixel offset tracking analyses. The results show that before the reservoir impoundment, the maximum accumulative displacements on the slope were more than 7 m from 2003 to 2008, while the post-impoundment displacements also exceeded 7 m in just 1 year from September 2009 to September 2010. Furthermore, this slope is still in active deformation up to now. Nevertheless, the displacement rates seem decreased recently according to the interferometric results of TerraSAR-X data pairs from September 2015 to March 2016.     

Comprehensive analyses of the initiation and landslide-generated wave processes of the 24 June 2015 Hongyanzi landslide at the Three Gorges Reservoir,China

Reservoir landslides pose a great threat to shipping safety, human lives and properties, and the operation of the hydropower station. In this paper, the 24 June 2015 Hongyanzi landslide at the Three Gorges Reservoir is considered as an example to study the initiation mechanism and landslide-generated wave process of a reservoir landslide. The finite difference method and limit equilibrium analysis are used to analyze the deformation and failure characteristics of the Hongyanzi slope. Simulation results show that a large deformation (about 358 mm) happens in the shallow deposits under intermittent rainfall condition, and the slope is in a limit state. At the same time, continuous rapid drawdown of the water level (about ?0.55 m/day during 8–24 June 2015) reduced the support and accelerated the drainage of the water for the bank slope. A coupling effect of intermittent rainfall and rapid drawdown of the water level was the triggering factor of the 24 June Hongyanzi landslide. Landslide-generated wave process was simulated using a fluid–solid coupling method by integrating the general moving object collision model. Simulation results show that the landslide-generated wave is dominated by the impulse wave, which is generated by sliding masses entering the river with high speed. The maximum wave height is about 5.90 m, and the wave would decay gradually as it spreads because of friction and energy dissipation. To prevent reservoir landslides, the speed for the rising or drawdown of the water level should be controlled, and most importantly, rapid drawdown should be avoided.     

Deformation response regularity of Liujiaba landslide under fluctuating reservoir water level condition

Due to the periodic rising and falling of the reservoir water level, the rock–soil body of bank slope is constantly changing between the saturated and unsaturated status, which changes the limit equilibrium condition of the slope body, resulting in a large number of dormant landslide reactivation and new landslide generation after water impounding operation of the three gorges reservoir. Based on the long-term monitoring data of pore-water pressure, water content, reservoir water level, rainfall and landslide deformation, the deformation response regularity of Liujiaba landslide under the fluctuating reservoir level combined scenario is studied in this paper. The results show that the landslide deformation is mainly in the lower section affected by the fluctuation of the reservoir water. The slide deformation appears in the mid-early stage of the water level declining and during the running of 175 m water level. The deformation is gradually increasing from a slowly to rapidly stage, then slows down and gradually reduces to a relative stopped state. Considering that the variation of the saturation line in the landslide will be influenced by the water level fluctuation rate, the SEEP and SLOPE modules are used with Geo-studio software for the fluctuant reservoir level and response pattern of landslide deformation analysis. The study can be provided as a reference for landslides study of debris aggradational landslide.     

Can vein-filling speleothems constrain the timing of deep-seated gravitational slope deformation? A case study from the Vinschgau (Italian Alps)

The steep, south facing slopes of the central Vinschgau (Val Venosta, South Tyrol, northern Italy) are characterized by deep-seated compound rockslides affecting 51 km² and reaching beneath the Quaternary valley fill. Morphological features include double ridges, trenches, scarps, and counterscarps, whereby the extent of displacement rises from W to E. Near the toe of these slopes, abundant fractures are present whose orientation and spatial strongly suggest that they are related to the gravitational slope deformations. These fractures host carbonate speleothems which are associated with local tufa occurrences at the surface. Given that the metamorphic host rock is essentially carbonate-free, these carbonate deposits require extensive water-rock interactions to form. Modern springs along the toe of the slope are also mostly supersaturated with respect to calcite and locally also aragonite. The invariant chemical composition, very low tritium levels, and in particular the low oxygen isotope values indicate that this groundwater infiltrates at high elevation and is characterized by a long residence time. On the other hand, local infiltration in the lower reaches of the slope is very limited due to the semiarid climate and is incompatible with the measured groundwater stable isotope composition and the high degree of mineralization. We therefore propose a conceptual model which reconciles the deep-seated gravitational slope deformation with the occurrence of mineralized groundwater and associated carbonate precipitates in fractures near the toe of the slope. These deposits provide a means to place constraints on the timing of rock fracturing and hence the slope movements. U/Th dating of 34 samples from eight sites shows that speleothem deposition started 14.2 ka BP and occurred semi-continuously throughout the Holocene. Thus, gravitational displacements likely commenced with a lag of ~3–4 ka after the deglaciation of the valley, which is also consistent with the few available dates on the onset of other deep-seated slope deformations in the Alps.     

Chasing a complete understanding of the triggering mechanisms of a large rapidly evolving rockslide

Rockslides in alpine areas can reach large volumes and, owing to their position along slopes, can either undergo large and rapid evolution originating large rock avalanches or can decelerate and stabilize. As a consequence, in particular when located within large deep-seated deformations, this type of instability requires accurate observation and monitoring. In this paper, the case study of the La Saxe rockslide (ca. 8 × 10⁶ m³), located within a deep-seated deformation, undergoing a major phase of acceleration in the last decade and exposing the valley bottom to a high risk, is discussed. To reach a more complete understanding of the process, in the last 3 years, an intense investigation program has been developed. Boreholes have been drilled, logged, and instrumented (open-pipe piezometers, borehole wire extensometers, inclinometric casings) to assess the landslide volume, the rate of displacement at depth, and the water pressure. Displacement monitoring has been undertaken with optical targets, a GPS network, a ground-based interferometer, and four differential multi-parametric borehole probes. A clear seasonal acceleration is observed related to snow melting periods. Deep displacements are clearly localized at specific depths. The analysis of the piezometric and snowmelt data and the calibration of a 1D block model allows the forecast of the expected displacements. To this purpose, a 1D pseudo-dynamic visco-plastic approach, based on Perzyna’s theory, has been developed. The viscous nucleus has been assumed to be bi-linear: in one case, irreversible deformations develop uniquely for positive yield function values; in a more general case, visco-plastic deformations develop even for negative values. The model has been calibrated and subsequently validated on a long temporal series of monitoring data, and it seems reliable for simulating the in situ data. A 3D simplified approach is suggested by subdividing the landslide mass into distinct interacting blocks.     

Understanding the triggering mechanism and possible kinematic evolution of a reactivated landslide in the Three Gorges Reservoir

More than 5000 landslides or potential landslides have been induced in the Three Gorges Reservoir (TGR) region since the impoundment in 2003, which have caused great damage and remain a huge threat to the dam and people living in the reservoir area. Understanding the deformation characteristics and failure mechanism of the landslides can be helpful in stability evaluation and landslide prediction. The primary aim of this study is to research the characteristics of the landslide motion and its relationships with environmental triggers, taking the Quchi landslide, a large, slow-moving, reactivated landslide in the TGR region, as an example. The instability clearly showed visible signs of movements since 2002, and after that, the slope has been experiencing persistent deformation. By combining 4 years of meteorological, hydrological data with displacement measurements from open fractures, deep boreholes, and surface points, as well as in situ observations, this paper reports the geological and geotechnical investigations performed to define the movement. The deformation is believed to be governed by reservoir water levels, while the precipitation has a minor effect. Seasonally, the slope movement has a very distinctive pattern with large deformation starting abruptly right after reservoir drawdown in June and lasting into late summer (September). Then there is a rapid transition to constant deformation (almost no displacement) as the reservoir level rises. The slope displacements appear to gradually increase every year, which suggests very high possibility of the large and overall failure of the slide. Both monitoring results and geomorphological observations have highlighted that the two active slide masses Q1 and Q2 would probably collapse in different kinematic evolution modes, i.e., the multistage failure and whole sliding motion.     

Landsliding triggered by reservoir operation: a general conceptual model with a case study at Three Gorges Reservoir

The Three Gorge Reservoir, one of the largest civil engineering projects in human history, dams the Yangtze River to form a 660-km-long and 1.13-km-wide reservoir. Today, although the project has been completed and is in normal operation, the on-going landslide initiation and movement in response to the reservoir operating is one of the main geologic hazards. The Huangtupo (meaning “yellow soil slope” in Chinese) Slope typifies such on-going landslides along the reservoir. Observations from a multi-year monitoring program conducted on this slope indicate that there are multiple slides on the reservoir banks that move episodically into the reservoir and their movements appear to be highly correlated with the initial and seasonal changes in the reservoir pool level. A hydro-mechanical numerical model is constructed to investigate the quantitative links among the episodic movements and the variations in pore water pressure, suction stress, hydrostatic reservoir water loading, and slope self-weight induced by the fluctuating water levels. Modeling results identify regions within the variably saturated slope where significant changes in stress occur during the periods of the initial impoundment that raised water levels from 68 to 135 m and that occur in response to seasonal fluctuations of the reservoir pool level between 145 and 175 m. We find that the rise or decline of reservoir pool level can either increase or decrease the stability of landslide. In general, hydrostatic reservoir water loading has positive correlation with the stability; pore water pressure and suction stress have negative correlation with the stability; and the effects of slope self-weight depend on the dip angle and mechanical properties of sliding surface.     

Analysis of a progressive slope failure in the Xiangjiaba reservoir area,Southwest China

The rehabilitation construction in the reservoir area of Xiangjiaba hydropower station in Southwest China has caused many landslides. A shallow progressive failure that occurred on the resettlement site of Xin’an Town of Pingshan County in Sichuan Province was selected as a case study. This landslide occurred in a long and gently inclined area by slope excavation under rainfall conditions. It is about 3.0 m deep with a total length of 35 m and is composed of some subfailures. Undisturbed samples were retrieved, on which the basic properties, shear strength, expansive potential, mineral compositions, and microstructures were tested and analyzed. The results show (1) the landsliding materials belong to medium expansive soil, consisting of the clay minerals of illite–smectite (I/S) and chlorite–smectite (C/S); (2) shear strength of the soil is sensitive to water, which greatly decreases once saturated; and (3) many fractures and relatively large pores are developed in the soils. Back analysis of the landslide shows that the shear strength at failure is less than the residual shear strength obtained from lab tests, indicating that some processes contributing to the slope failure could not be reflected by the shear box test. Based on the above analysis, the progressive process of the slope failure was interpreted, and it is inferred that the rainfall entered into the slope mainly through fractures and relatively large pores in the soil. It caused not only the great decrease in soil strength but also the swelling trend. The latter one would lead to growth, interaction, and coalescence of the fractures. Soon after, these fractures formed the shear planes (zones), which further decreased the resistance of the landslide. Under these favorable conditions, the slope excavation directly triggered the failure.     

How does the water–rock interaction of marly rocks affect its mechanical properties in the Three Gorges reservoir area,China?

Marly rock is a sensitive rock group of landslides in the Three Gorges reservoir area, China. It is composed predominantly of carbonate and clay minerals, water–rock interaction (WRI) of which could activate landslides in the reservoir area. To study the mechanism by which WRI affects the mechanical properties of marly rock, samples were collected from two boreholes (depth 301.78 and 307.14 m) and slope surface. Then, laboratory tests were designed to study the quantitative relationship between mineral contents and mechanical properties of intact rock, to analyze both change process of mineral composition and microstructure under short-term and long-term WRI. Finally, the change in mechanical properties and its effect on slope stability are suggested. This study indicates that the uniaxial compressive strength and Poisson ratio can be estimated by linear regression equations: (1) σ _c = 8.959 × (C/Q) ? 0.744 × CM + 58.516; (2) μ = 0.014 × (C/Q) ? 0.001 × CM + 0.234. The chemical reactions of WRI mainly included dissolution and ion exchange. On the slope surface, dissolution mainly acts on calcite, illite, dolomite, feldspar and other minerals dissolved in water. Underground, both chemical reactions of dissolution and ion exchange easily approach equilibrium with long-term seepage. Small-size minerals and micropores damage the stable microstructure of marly rock. These changes of minerals and microstructure can trigger shallow slope failure and develop deep creep deformation along some crash zones in the reservoir shoreline.     

基于Hoek-Brown准则的三维边坡变形稳定性分析

采用Hoek-Brown准则,分析三维边坡在开挖扰动下的变形稳定性。以某露天矿边坡为工程背景,利用快速拉格朗日差分法(FLAC3D)建立三维数值分析模型,并在边坡中布置若干监测点,利用FISH语言编制相应位移插值程序,探讨边坡开挖引起的动静态位移响应,从宏观角度揭示出边坡开挖后,不同区域的变形,为工程实践提供指导;介绍了强度折减技术在Hoek-Brown准则中的实施方法,采用计算不收敛失稳判据,计算边坡安全系数,从而进一步推广Hoek-Brown强度折减法在三维边坡稳定性分析中的应用。     

Morphological analysis of deep-seated gravitational slope deformation (DSGSD) in the western part of the Argentera massif. A morpho-tectonic control?

The western part of the Argentera–Mercantour massif (French Alps) hosts very large currently active landslides responsible of many disorders and risks to the highly touristic valleys of the Mercantour National Park and skiing resorts. A regional scale mapping of gravitational deformations has been compared to the main geo-structures of the massif. A relative chronology of the events has been established and locally compared to absolute ¹⁰Be dating obtained from previous studies. Two types of large slope destabilisations were identified as follows: deep-seated landslides (DSL) that correspond to rock volumes bounded by a failure surface, and deep-seated gravitational slope deformations (DSGSD) defined as large sagging zones including gravitation landforms such as trenches and scarps or counterscarps. Gravitational landforms are mainly collinear to major N140°E and N020°E tectonic faults, and the most developed DSGSD are located in areas where the slope direction is comparable to the orientation of faults. DSL are mostly included within DSGSD zones and located at the slopes foot. Most of DSL followed a similar failure evolution process according to postglacial over steepened topographies and resulting from a progressive failure growing from the foot to the top of the DSGSD that lasts over a 10 ky time period. This massif-scale approach shows that large-scale DSGSD had a peak of activity from the end of the last deglaciation, to approximately 7000 years bp. Both morphologic and tectonic controls can be invoked to explain the gravitational behaviour of the massif slopes.     

Geochemical fractionation of manganese in the Riogrande II reservoir, Antioquia, Colombia

The Riogrande II reservoir in Colombia has a total storage capacity of 240 million m³ and lies 2,270 m above sea level. The reservoir is used for power generation, water supply and environmental improvement. Dissolved manganese (Mn) is removed from reservoir water dedicated to domestic use by purification processes. Removal of Mn, however, poses a major challenge to purification processes and warrants the study of ways to naturally reduce dissolved Mn levels in the reservoir. The source of Mn within the reservoir is not well understood, however, presumably arises from sediment mobilization initiated by variation in pH, redox potential (ORP or Eh), dissolved oxygen (O₂) and ionic strength conditions. This study investigated conditions within the reservoir to further understand Mn transfer from the sediment into the water column. O₂, pH, oxidation–reduction potential (ORP or Eh), organic matter content and electric conductivity were measured in water samples and sediment from the reservoir. Sequential extraction (SE) procedures were used to test the specific effects exerted by each of these conditions on Mn mobilization from the sediments. The European Community Bureau of Reference (BCR) sequential extraction procedure was used to quantify metals in sediment (referred to as the BCR extraction below). Statistical analysis of geochemical data from water samples (both water column and sediment pore water) and sediments demonstrated the conditions under which Mn can be released from sediments into the water column. The results indicated a primarily oxic water column and anoxic reducing conditions in the sediment (ORP or Eh ≤ ?80 mV). The pH of water in contact with bottom sediments varied from 7.6 to 6.8. The pH of sedimentary pore water varied from 6.8 to 4.7. The sediments contained significant amounts of organic matter (20 %). Chemical extractions showed that the exchangeable fraction contained over 50 % of the total Mn within sediments. Microscopic analysis using scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) indicated that Mn does not occur within well-crystallized mineral phases in the Riogrande II sediments. A large proportion of Mn exists instead as material adsorbed onto the surfaces of recently deposited sediment particles. Bacterial oxidation of organic matter may cause the observed anoxic conditions at the bottom of the reservoir. Mineralization of organic matter therefore contributes to reducing conditions within the sediments. Mobilization of Mn from the sediment into the water column may result from reductive dissolution of this fraction. Manganese release by this mechanism diminishes the water quality of the Riogrande II reservoir and warrants further study.     

高陡山区房柱法开采岩体移动预测及山体失稳判据

在实测资料统计分析基础上,以概率理论为基础,建立了高陡山区房柱法地下开采岩体移动变形预测分析模型,并给出了岩体变形破坏的极限值。利用本模型对山区地下开采工程实例进行了具体的计算分析,通过工程实例分析说明,理论预测结果与现场实测结果吻合。     

A review of b-value imaging and fractal dimension studies in the Andaman Sumatra subduction

The present study analyses the spatial pattern of quaternary gravitational slope deformations (GSD) and historical/present-day instabilities (HPI) inventoried in the Swiss Rhone Valley. The main objective is to test if these events are clustered (spatial attraction) or randomly distributed (spatial independency). Moreover, analogies with the cluster behaviour of earthquakes inventoried in the same area were examined. The Ripley’s K-function was applied to measure and test for randomness. This indicator allows describing the spatial pattern of a point process at increasing distance values. To account for the non-constant intensity of the geological phenomena, a modification of the K-function for inhomogeneous point processes was adopted. The specific goal is to explore the spatial attraction (i.e. cluster behaviour) among landslide events and between gravitational slope deformations and earthquakes. To discover if the two classes of instabilities (GSD and HPI) are spatially independently distributed, the cross K-function was computed. The results show that all the geological events under study are spatially clustered at a well-defined distance range. GSD and HPI show a similar pattern distribution with clusters in the range 0.75–9 km. The cross K-function reveals an attraction between the two classes of instabilities in the range 0–4 km confirming that HPI are more prone to occur within large-scale slope deformations. The K-function computed for GSD and earthquakes indicates that both present a cluster tendency in the range 0–10 km, suggesting that earthquakes could represent a potential predisposing factor which could influence the GSD distribution.     

海底缓坡场地地震侧移数值分析方法

地震动使海底倾斜土层软化、液化并产生永久变形和位移。基于有限元理论,提出一种海底缓坡场地地震引起水平侧移的数值计算方法,将波浪荷载简化为恒定压力荷载和初始孔压,采用二维有效应力动力有限元分析方法进行液化分析,同时由模量软化理论得到土层在地震动各时段的模量,通过非线性静力方法计算软化、液化引起的水平侧移。由算例分析了土层坡度、液化层及上覆非液化层厚度、波浪荷载等因素对侧移的影响,通过对比分析表明了该方法的有效性,可为近海工程场地地震地质灾害评价提供参考数据。     

Unknown large ancient earthquakes along the Kurai fault zone (Gorny Altai): new results of palaeoseismological and archaeoseismological studies

Palaeoseismological and archaeoseismological studies in the Kurai fault zone, along which the Kurai Range is thrust onto Cenozoic deposits of the Chuya intramontane basin, led to the identification of a long reverse fault scarp 8.0 m high. The scarp segments are primary seismic deformations of large ancient earthquakes. The scarp’s morphology, results of trenching investigations, and deformations of Neogene deposits indicate a thrusting of the piedmont plain onto the Kurai Range, which is unique for the Gorny Altai. Similarly for Northern Tien Shan, we explain this by the formation of both a thrust transporting the mountain range onto the depression and a branching thrust dislocation that forms the detected fault scarp. In a trench made in one of the scarp segments, we identified the parameters of the seismogenic fault – a thrust with a 30° dipping plane. The reconstructed displacement along the fault plane is 4.8 m and the vertical displacement is 2.4 m, which indicates a 7.2–7.6 magnitude of the ancient earthquake. The ¹⁴C age of the humus-rich loamy sand from the lower part of the colluvial wedge constrains the age of the earthquake at 3403–3059 years BP. Younger than 2500 years seismogenic displacements along the fault scarp are indicated by deformations of cairn structures of the Turalu–Dzhyurt-III burial mound, which was previously dated as iron age between the second half of I BC and I AD.     

Hydro-mechanically coupled finite-element analysis of the stability of a fractured-rock slope using the equivalent continuum approach: a case study of planned reservoir banks in Blaubeuren,Germany

Construction works associated with the building of reservoirs in mountain areas can damage the stability of adjacent valley slopes. Seepage processes caused by the filling and drawdown operations of reservoirs also affect the stability of the reservoir banks over time. The presented study investigates the stability of a fractured-rock slope subjected to seepage forces in the lower basin of a planned pumped-storage hydropower (PSH) plant in Blaubeuren, Germany. The investigation uses a hydro-mechanically coupled finite-element analyses. For this purpose, an equivalent continuum model is developed by using a representative elementary volume (REV) approach. To determine the minimum required REV size, a large number of discrete fracture networks are generated using Monte Carlo simulations. These analyses give a REV size of 28?×?28 m, which is sufficient to represent the equivalent hydraulic and mechanical properties of the investigated fractured-rock mass. The hydro-mechanically coupled analyses performed using this REV size show that the reservoir operations in the examined PSH plant have negligible effect on the adjacent valley slope.     

Site scale modeling of slow-moving landslides,a 3D viscoplastic finite element modeling approach

This paper presents an advanced 3D numerical methodology to reproduce the kinematics of slow active landslides, more precisely, to reproduce the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. For this purpose, finite element analyses are performed in a large area covering a long time-span (12 years), in order to exhibit different interacting slope movements. First, we perform a stability analysis using the shear strength reduction (SSR) technique with a Mohr-Coulomb failure criteria. It is done in order to compute factors of safety (FS) and to identify two different scenarios, the first one being stable (FS > 1) and the second one being unstable (FS < 1). In the studied test case, the Portalet landslide (Central Spanish Pyrenees), the first scenario corresponds to an initial stable configuration of the slope and the second one to an unstable excavated configuration. Second, taking the first scenario as an initial condition, a time-dependent analysis is performed using a coupled formulation to model solid skeleton and pore fluids interaction, and a simplified ground water model that takes into account daily rainfall intensity. In this case, a viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behavior and the delayed creep deformation due to the excavation. The fluidity parameter is calibrated to reproduce displacements measured by the monitoring systems. Our results demonstrate that 3D analyses are preferable to 2D ones for reproducing in a more realistic way the slide behavior. After calibration, the proposed model is able to simulate successfully short- and medium-term predictions during stages of primary and secondary creep.     

Seismic Stability Analysis of a Himalayan Rock Slope

The seismic slope stability analysis of the right abutment of a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India, is presented in this paper. The rock slopes are composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Seismic slope stability analysis of the slope under consideration is carried out using both pseudo-static approach and time response approach as the site is located in seismic zone V as per the earth quake zonation maps of India. Stability of the slope is studied numerically using program FLAC. The results obtained from the pseudo-static analysis are presented in the form of Factor of Safety (FOS) and the results obtained from the time response analysis of the slope are presented in terms of horizontal and vertical displacements along the slope. The results obtained from both the analyses confirmed the global stability of the slope as the FOS in case of pseudo-static analysis is above 1.0 and the displacements observed in case of time response analysis are within the permissible limits. This paper also presents the results obtained from the parametric analysis performed in the case of time response analysis in order to understand the effect of individual parameters on the overall stability of the slope.