Seismic Slope Stability Research Articles

산사면의 지진동 증폭 특성

지진 시 산사면의 안전성은 일반적으로 유사정적해석법이나 Newmark 변위법으로 평가된다. 두가지 방법에서 모두 사면에서의 최대가속도를 정의해야 하며 이는 설계기준에 제시된 지진계수를 이용하여 산정한다. 하지만 지진계수는 수평지반 지표면에서의 최대응답을 나타내므로 사면에는 원칙적으로 적용 가능하지 않다. 본 연구에서는 산사면에서의 증폭계수를 도출하기 위하여 다양한 두께와 전단파속도의 산사면에 대한 일련의 2차원 유사정적해석과 동적해석을 수행하였다. 산사면의 증폭계수는 수평지반과는 다르게 지표면에서의 응답을 적용하는 것이 아니라 시간이력에 따라 사면 파괴토체 내부에서 발생하는 모든 가속도합의 최대값과 암반노두에서의 최대지반가속도의 비율로서 계산하는 방법을 새롭게 적용하였다. 이와 같이 계산된 증폭계수는 평균값이 1에 가까우며 사면토체의 평균가속도는 크게 증폭되지 않는 것으로 나타났다. 경사가 30o인 산사면의 증폭계수는 수평지반의 계수에 비해서 14-50% 작은 것으로 나타났다. 이는 사면의 정상부 및 지표면 부근에서는 크게 증폭이 되지만 하부경계면에서는 증폭이 작아서 평균을 계산하였을 경우 작아지기 때문이다. 결론적으로, 수평지반에 대해서 제시된 증폭계수를 산사면에 적용할 경우, 증폭을 크게 과대예측할 수 있으므로 본 연구에서 제시된 증폭계수를 사용하는 것이 보다 합리적일 것으로 판단된다. Seismic stability of slopes is most often assessed through pseudo-static analysis or Newmark displacement method. In both types of analyses, it is necessary to define the maximum acceleration of the slope. It is current practice to determine the acceleration using the seismic site coefficients. However, the site coefficients are not compatible with slopes, since they were developed for horizontally layered soil profiles. In this study, a series of pseudo-static and dynamic analyses are performed on various mountain slopes, from which the amplification factors are derived. A new method for calculating the amplification factors is proposed in this study. In a slope, the ground acceleration varies in both the vertical and horizontal directions. In the proposed procedure, the calculated accelerations at each node inside the slope failure mass are summed. The amplification factor is defined as the ratio of the average acceleration of the soil mass to the rock outcrop peak acceleration. The factors calculated using the proposed method is shown to be close to 1 for mountain slopes modeled in this study. The factors are approximately 14-50% lower than coefficients developed for horizontal soil deposits. The derived factors are lower because even though the amplification at the slope crest is high, as well as on the surface of the slope, the amplification is low near the bottom of the soil layer. In summary, it is demonstrated that the use of the site coefficients derived for horizontally layered soil profile will lead to significant conservative estimate of the slope stability.

Slope seismic stability analysis on kinematical element method and its application

In this paper, kinematical element method (KEM) is extended to the solution of seismic slope stability with the pseudo-static approach. Analytical expressions are derived to calculate the factor of safety of slopes subjected to seismic loading and pore-water pressure. KEM is adopted to assess seismic stability of slope and some examples show that the results obtained from KEM, limit equilibrium method (LEM), variational method and strength reduction method (SRM) are generally in good agreement. And then the seismic slope stability charts are developed on the basis of KEM and pseudo-static approach, providing a rapid and reliable way to calculate the factor of safety and the location of critical slip surface without iteration. Based on the above seismic slope stability charts, a new back analysis method is presented. KEM and pseudo-static approach are applied to study the effect of blasting on the stability of open pit slope, and the approach to determine the relationship between critical explosive weight and distance is presented.

Pseudo-Static and Pseudo-Dynamic Stability Analysis of Tailings Dam Under Seismic Conditions

In this paper the seismic slope stability analyses are performed for a typical section of 44 m high water retention type tailings earthen dam located in the eastern part of India, using both the conventional pseudo-static and recent pseudo-dynamic methods. The tailings earthen dam is analyzed for different upstream conditions of reservoir like filled up with compacted and non-compacted dumped waste materials with different water levels of the pond tailings portion. Phreatic surface is generated using seepage analysis in geotechnical software SEEP/W and that same is used in the pseudo-static and pseudo-dynamic analyses to make the approach more realistic. The minimum values of factor of safety using pseudo-static and pseudo-dynamic method are obtained as 1.18 and 1.09 respectively for the chosen seismic zone in India. These values of factor of safety show clearly the demerits of conventional pseudo-static analysis compared to recent pseudo-dynamic analysis, where in addition to the seismic accelerations, duration, frequency of earthquake, body waves traveling during earthquake and amplification effects are considered.

3-D Seismic Response Analysis Methods of High Core Rockfill Dams

Based on dynamic triaxial test data of dam materials, a dynamic constitutive model is suggested. Combining with construction of a high core rock-fill dam, several key issues, such as dam seismic response, seismic slope stability, dam permanent deformation, filter layer anti-liquefaction, and dynamic strength of the core wall are analyzed using 3-D dynamic effective stress analysis method. Some useful conclusions and regularity are obtained in aspects of seismic response and anti-seismic properties. The analysis method and conclusions could be referred to the analogous engineering.

Seismic Slope Stability of the Tipaimukh Dam of North-Eastern India: A Numerical Modelling Approach

This article represents the seismic slope stability analysis of earth core rock-fill Tipaimukh Dam under static and dynamic loading conditions. The Tipaimukh area is located at the triple junction of the three continental plates- Indian, Eurasian and Burmese tectonic plate. The area is frequently interrupted by unanticipated geological discontinuities, such as regional and local-scale faults and fractures that behave as a strike-slip and extensional movements. Two kinds of numerical models (A and B) are presented here. Both models consist of five zones and each zone has individual rock mechanical characteristics. Model A assumes safety factor of dam slope associated with impervious core including clay material. Model B assumes also safety factor associated with masonry wall as an impervious core. The present numerical modeling results reveal that under static condition of the dam the safety factor ranges from 2.56 to 2.69. On the contrary, under seismic/dynamic loading conditions associated with earthquake M6.0 to M8.5, the safety factor ranges from 1.60 to 0.98 for model A, and from 1.66 to 0.98 for model B. The past records of the historical earthquakes in north-eastern India reveal that the recurrence period of intensive magnitude earthquakes, as experienced in Assam, Shillong plateau and Manipur area, is 38 to 53 years. The calculated safety factor of the Tipaimukh Dam implies that the dam would be destroyed if it would be affected by earthquakes magnitude over 7.0 throughout its operational life, which is usually extent from 50 to 100 years.

하계해석을 이용한 수직방향 지진계수 영향에 따른 비탈면의 안정성 평가 연구

최근에 발생한 아이티지진, 칠레지진의 지진파 기록에서 일반적으로 비탈면 안정해석에서 무시되었던 수직방향 지진가속도 성분이 크게 나타났다. 특히, 수직방향 지진성분은 진원이 내륙에 위치한 경우 더욱 뚜렷하게 나타난다. 그러므로 설계에 수직방향 지진성분을 고려하지 않은 지반 구조물들은 많은 인명과 재산 피해를 가져올 수 있다. 따라서, 본 연구는 지진계수비에 따른 수평방향 항복지진계수의 하계해를 산정하였고, 비탈면 안정성에 미치는 영향을 평가하였다. 또한, 한계상태 수직방향 지진계수의 방향(상향, 하향)을 결정할 수 있는 관계식을 제안하였다. Recent earthquake records indicate that the vertical component of earthquake loading, generally neglected in seismic slope stability analysis, has a significant influence on the stability. This is particularly true for the earthquakes originating inside the continent, not from its boundaries. Therefore the design of geotechnical structures without consideration of vertical component of earthquake loading may result in unsafe design. In this study, with a consideration of the effect of vertical seismic loading, the horizontal yield seismic coefficients under various slope conditions are estimated, using the lower bound limit analysis. In addition, the equation for the determination of the critical direction (either upward or downward) of vertical seismic loading is proposed.

Block Element Analysis for Earthquake Response of Joint Rock Slope

In this paper, the Block Element Method (BEM) for dynamic analysis is developed and applied to historical analysis of seismic stability of a rock slope. Combine the idea of viscous-spring boundary with the theory of BEM, the artificial boundary condition of BEM is formulated, which can eliminate reflection of the seismic waves from the boundaries of the calculating domain. Also, the relationship between the displacement and the stiffness of discontinuous is adopted in the dynamic block element method. The corresponding program is written by FORTRAN language and the application of the intake slope demonstrates the capacity of this method.

Advanced seismic slope stability analysis

The objective of this study was to present an advanced methodology for assessing seismic slope stability by taking into account the uncertainties related to the main input parameters. The methodology was applied on a real landslide in order to show the advantages of using the proposed procedure and establish the baseline trends of dynamic response and calculated permanent seismic displacements. It involves the following steps: preliminary analysis, probabilistic static and seismic factor of safety analysis, and permanent seismic displacement analysis. Estimating post-failure maximum seismic deformation of landslide mass and sounding properties is the most important part of this study. It involves both Newmark sliding block method and continuum mechanics approach, applied for characteristic set of input values in order to have more accurate assessment of slope performance and determine the relative importance of input parameters. The results of the analysis showed the benefits of using the proposed step-by-step methodology. The obtained difference in the results between the two methods depends strongly on the set input data for a particular analysis.

Regression analysis for seismic slope instability based on a double phase viscoplastic sliding model of the rigid block

Semi-empirical models based on Newmark’s sliding block permit the estimation of expected co-seismic displacements in relation to one or more parameters which characterize the ground motion that theoretically caused them. Taking this into consideration, a regression analysis, based on a double-phase viscoplastic (DPV) model, was developed using 96 Italian ground motion accelerograms for a total of 1,448 combinations obtained for different parametric conditions of the indefinite slope model. Repeated stability analysis, performed by means of the DPV model, allows for the assessment of the seismic instability of a slope in relation to different reached behaviour levels, as well as seismically induced permanent displacements. At these behaviour levels, co-seismic increases and possible subsequent decreases of viscoplastic shear strengths are associated. This implies that the post-seismic persistent mobility (collapse) of the slope can be obtained from the computation. On the other hand, coherently with the increasing of shear resistances during fast sliding displacements in clay soils, the seismic-forced displacements result substantially lower than corresponding values obtained by means of the rigorous Newmark’s sliding block. In addition, in relation to some seismic ground motion parameters, regression and functional border and separation curves were obtained with the aim of providing an expeditious seismic slope stability evaluation in reference to the co-seismic and post-seismic behaviour of clayey slopes. Regarding this, the real behaviour of two historical landslide events is discussed in the light of the results of the regression analysis outlined in this work.

On the seismic stability analysis of reinforced rock slope and optimization of prestressed cables

The evaluation of the seismic stability of high rock slopes is of vital importance to ensure the safe operation of the hydropower stations. In this paper, an equivalent pseudo-static force analysis based on the finite element method is developed to evaluate the seismic stability of reinforced rock slopes where the prestressed cables are modeled by the bar elements applied with nodal forces and bounded only at the anchored parts. The method is applied to analyze a high rock slope in south-west China and the optimization of cables. The stabilization effects of prestressed cables on the seismic stability of the slope are studied, the simulations of the concrete heading are discussed and the potential failure modes of the shear concrete plug are compared. Based on this, the optimization of cables is studied including the anchor spacing and inclined angles.

Influence Factors on Highway High Slope Seismic Stability and Preventive Measures

Highway high slope seismic stability is an urgent problem need to be solved, and the existing specifications can not meet the needs of engineering in design methods, construction measures and enforceability. Based on the earthquake failure mechanism of high slope, this paper analyzes the impact factors on highway high slope seismic stability, and puts forward earthquake preventive measures for high slope.

Regional Arias Intensity Attenuation Relationship for Taiwan Considering VS30

The Arias intensity is a measure of earthquake intensity arrived at through the integration of a square of the acceleration time history. It has been demonstrated to be an effective predictor of earthquake damage potential in relation to short-period structures, liquefaction, and seismic slope stability, and has begun to be considered as a ground-motion measure suitable for use in probabilistic seismic hazard analysis (PSHA), as well as earthquake loss estimation. A new empirical Arias intensity attenuation relationship for shallow crustal earthquakes is developed where both fault type and a continuous site variable VS30 are considered. The relationship is based on a large number of strong-motion records (6570) from a wide range of earth- quake magnitudes (3.9-7.6) from the Taiwan Strong Motion Instrument Program (TSMIP) network. Its functional form is modified from that of Travasarou et al. (2003), which is derived from a point-source model, and the coefficients are determined through nonlinear regression analyses using a mixed-effects model. The results show that the incorporation of VS30 can significantly reduce regression error. The Arias intensity value predicted in the present study is generally similar to that obtained by Travasarou et al. (2003), but is different in detail, being more suitable for usage in PSHA for a tectonically young orogenic belt like that in Taiwan or New Zealand.

Stability Analysis of Reinforced Slopes Using Upper Bound Limit Analysis Method

The kinematic method of limit analysis approach is applied to study stability of reinforced slopes. The amount and length of reinforcement required to prevent the slope to collapse are determined based on different mechanisms. A new method consisting of horizontal blocks is used in translational mechanism. The failure wedge is divided into a number of horizontal slices involving reinforcements. The reinforcements do not intersect the slices. Thus, they have no direct influence on the inter-slice forces. The presented method can reduce difficulties of stability analysis for reinforced slopes. In this paper, the seismic stability of slopes reinforced with geosynthetics is investigated. The seismic analysis procedure is substituted with pseudo-static horizontal forces. While such an approach ignores the acceleration history of a structure, it is routinely used in practice. It has been assumed that the geosynthetics are uniformly distributed in the height of slope. Based on these assumptions, different possible failure mechanisms are considered and necessary analytical expressions for determining the design parameters are derived for each mechanism. The results of these analyses are presented to illustrate the influence of different parameters such as geometrical parameters of slopes, soil characteristics, and seismic forces on the stability of reinforced earth structures.

A grade-3 method of zonation for seismic slope stability: An Italian case study

This paper presents a seismic microzonation study performed in an area of the Northern Apennines (Italy) in order to reduce the level of risk from landslide hazard, to support decisions in urban planning and to provide useful information for building design. The area in question measures about 2.6km2 and is characterised by considerable landslide susceptibility also in non seismic conditions as evidenced by a number of surveys carried out over the past years. The slope deposit, lying over a marley-arenaceous formation, shows a variable thickness from a few metres to 30m and consists of fine silty-clay, clay-sandy and silty-sandy soil in a variable amount. Quiescent and active landslide areas with ground movements involving the shallowest layers of the soil deposit have been detected.Given the relatively high seismicity of the region, the aim of this study is to describe the principles and criteria adopted in a seismic risk analysis conducted over a limited area in order to carry out a very high and detailed level of zonation for ground motion and slope stability (i.e., Grade 3 according to the definition in the Manual for Zonation on Seismic Geotechnical Hazards). For this purpose, reliable expected earthquakes were assumed and in-depth geologic, geomorphologic, geotechnical and geophysical analyses were carried out to define a subsoil model for performing numerical analyses of local seismic response and slope stability in both non-seismic and seismic conditions. The proposed methodology consists of the following three steps: (i) identification of a number of seismic inputs for the numerical analyses; (ii) implementation of numerical analyses to evaluate the amplification of ground shaking and to assess potential for slope failure; (iii) mapping of homogeneous areas with respect to expected site amplifications and landslide risk. The study allowed the mapping of four zones which are expected to be homogeneous in terms of both amplification factor of seismic motion (FA) and safety factor against landslide (FS). Quiescent and active landslide zones were thus identified with greater accuracy together with the most probable sliding surfaces. For this purpose, a 1-D numerical code was adopted for seismic response analyses and limit equilibrium methods were implemented and numerically solved in static and pseudo-static slope stability analyses.

A New Method to Analyze Seismic Stability of Cut Soil Slope

A new method to analyze the seismic stability of the cut soil slope is suggested in this study. In the method, the limiting equilibrium theory and the stress analyzing method are used. The stress acceptability criterion is based on the limited strength of soil. Two basic assumptions are given in the method. One is that the slip surface can be replaced by a series of straight lines. The other is that the interslice boundary is an inclined plane. Three balance equations for any slice, which are two for force equilibrium and one for moment equilibrium, are proposed. An iterative method, which solves the balance equations from the first slice to the last slice, is also suggested. In the new method, the slip surface is not predefined, but is obtained slice by slice going from downhill to uphill in terms of the force and moment balance equations of the slice.

Seismic Slope Stability of Embankments Constructed with Pond Ash

Utilization of pond ash in large earthworks for geotechnical applications like construction of highway embankments, raising of ash dykes and filling low lying areas (construction fills), solves the waste disposal problem besides conserving the natural soils. However, design and construction of such geotechnical structures particularly in earthquake prone areas, requires thorough understanding of dynamic response of these structures under different seismic loading conditions. Here in this article, dynamic stability of embankments raised around the perimeter of ash ponds by the upstream and down stream methods of construction with coarse (ash from inflow point) and fine (ash from outflow point) pond ash materials, has been computed for different site specific earthquake scenarios appropriate for Delhi region. The performance of the embankments is analyzed using Quake/w and Slope/w software packages for steady-state seepage condition. The required dynamic properties of the materials are obtained form the various field and laboratory tests. The geotechnical structures constructed with ash exhibited similar type of response as that of with the natural soils. The performance of the structures is influenced by number factors such as type of construction (e.g. upstream or downstream), insitu conditions (e.g. stresses, density, phreatic line), and magnitude of dynamic loads, besides on the static and dynamic characteristics of the materials. The structures with the fine ash exhibit higher vulnerability to liquefaction related failures, which emphasizes need for carrying site-specific studies and adoption of proper construction measures to ensure design parameters.

Seismic Acceleration Distribution Analysis of High Earth-Rock Dams in Three-Dimensional Space

When pseudostatic method is employed to analyze slope seismic stability of high earth- rock dams, earthquake load is computed according to dynamic seismic coefficient figure in the present Specifications for Seismic Design of Hydraulic Structures (DL5073-1997). The figure is only suitable for earth-rock dams lower than 150m. While at the present time, many earth-rock dams to be constructed are higher than 150m. Compared with low dams, high order self-vibrating period of high dams is easy to coincide with seismic predominant period, and high order vibrations are constantly to be activated and amplified, which result in seismic acceleration distribution is different from low dams. With analytical and finite element method respectively, seismic acceleration distribution of high earth-rock dams is analyzed. Suggested dynamic seismic coefficient figure of earth-rock dams 300m-level in height is put forward, which offer a supplement for the present Code for Seismic Design of Hydraulic Structure.

Estimating Fully Probabilistic Seismic Sliding Displacements of Slopes from a Pseudoprobabilistic Approach

Permanent sliding displacements are used to evaluate the seismic stability of earth slopes, and current practice utilizes a pseudoprobabilistic approach to predict the expected sliding displacement. The pseudoprobabilistic approach specifies a design ground-motion level based on a probabilistic seismic hazard analysis and a specified hazard level (e.g., 2% probability of exceedance in 50 years), but the displacement is predicted deterministically based on the design ground-motion level. The fully probabilistic approach develops a hazard curve for sliding displacement, and it is used to assess the displacement of the slope for a given hazard level. Comparisons of the fully probabilistic and pseudoprobabilistic approaches indicate that the pseudoprobabilistic analysis provides nonconservative estimates of sliding displacement in most cases. This paper presents a modification to the pseudoprobabilistic approach that provides displacement values more consistent with the fully probabilistic approach. This modification involves specifying a displacement greater than the median, in order to take into account the uncertainty in the displacement prediction. The appropriate value of displacement above the median is a function of the ky/PGA value and the model used to predict the displacement.

Assessment of Embankment Factor Safety Using Two Commercially Available Programs in Slope Stability Analysis

Analysis of the static and seismic stability of natural and manmade slopes and embankments is a challenging geotechnical problem. Often, different professionals analyzing the same problem will estimate a wide variation in expected performance. The objective of this paper is to study the effect of earthquake shaking on slope stability using Geo Studio software 2007 and Plaxis 2D Program. The critical slip surface and factor of safety is obtained by using finite element, limit equilibrium, Morgenston – Price, and strength reduction and other method available in the used software. The applicability of the analysis is demonstrated by analysis various slope and embankments subjected to 0.5g dynamic load due to earthquake shaking. For simple homogenous soil slopes, it was found that the results from these methods are generally in good agreement. This study also investigated the effect of embankment height and its slopes (geometry) on stability and liquefaction due to the earthquake. Increasing embankment height and flattering it can enhance stability and reduced liquefaction zone. Liquefaction phenomenon which has produced to severe damage all over the world was studied under earthquake record of 0.5g. Four examples are providing to evaluation liquefaction effect and determination factor of safety as well as potential for liquefaction of soils. Variability of soil layers parameters affecting factor of safety and liquefaction have been studied for slopes.

Application of an Anisotropic Constitutive Model for Structured Clay to Seismic Slope Stability

The anisotropic nature of response and degradation of shear strength from the undisturbed condition to the remolded state are two fundamental and challenging aspects of response in some clay deposits. This paper presents a comprehensive, yet flexible and practical, version of the SANICLAY model and its application to a seismic slope-stability problem. The model is based on the well-known isotropic modified Cam-Clay model with two additional mechanisms to account for anisotropy and destructuration. The model has been efficiently implemented in a three-dimensional (3D) continuum, coupled, dynamic, finite-difference program. The program has been used to analyze the seismic response of clay slopes to gain better insight into the role of the previously mentioned parameters in real applications. Different aspects of the model, including anisotropy and destructuration, and their effects on the earthquake-induced strains and deformations in the slope have then been explored and presented. By providing a link between the model parameters and the soil’s undrained shear strength, which is a well-known engineering parameter, a benchmark comparison has been made between the results of the present advanced model and those of an engineering approach. To this end, a modified Newmark sliding-block analysis has been used, in which the yield acceleration is gradually reduced as block sliding progresses during the earthquake. It is observed that although the two analyses display the same trends, the modified Newmark sliding-block method provides conservative results compared with those obtained from the developed simulation model.