Seismic Slope Stability Analysis Research Articles

Seismic stability analysis of shallow overburden slopes with vegetation protection

Seismic stability analysis of shallow overburden slopes with vegetation protection

Seismic stability and failure mechanisms of gentle and steep slopes considering soil rotated anisotropy and spatial variability

The present study focuses on investigating the effects of soil rotated anisotropy and spatial variability on slope failure in seismic conditions. The random finite element method aided by subset simulation is implemented, which ensures an efficient quantification of both the probability of failure and its associated consequence of failure. Several slope angles of gentle and steep slopes and soil properties that lead to a low probability of failure were selected for parametric studies. The comprehensive parametric studies of seismic slope stability analysis consider various factors such as slope inclinations, seismic coefficients, scales of fluctuation, and orientations of the major principal scale of fluctuation (i.e., the rotation angle of random field). The results underscore the importance of considering the combined effects of soil anisotropy and the orientation of the major principal scale of fluctuation for designing both gentle and steep slopes under seismic conditions and emphasize that care must be given to ensure the worst-case scenario is considered. Visual observations of failure mechanisms of gentle and steep slopes under seismic conditions were also shown to be very helpful in interpreting the variation of probability of failure due to soil spatial variation.

Stability Analysis of Seismic Slope Based on Relative Residual Displacement Increment Method

The seismic stability analysis of a slope is a complex process influenced by earthquake action characteristics and soil mechanical properties. This paper presents a novel seismic slope stability analysis method using the relative residual displacement increment method in combination with the strength reduction method (SRM) and the actual deformation characteristics of the slope. By calculating the relative displacement of the key point inside the landslide mass and the reference point outside the landslide mass after each reduction, the safety factor of the slope is determined by the strength reduction factor (SRF) corresponding to the maximum absolute value of the relative residual displacement increment that appears after a continuous plastic penetration zone. The method eliminates interference caused by significant displacement fluctuations of key points under earthquake action and reduces the subjective error that can occur when manually identifying displacement mutation points. The proposed method is validated by dynamic calculations of homogeneous and layered soil slopes and compared with three other criteria: applicability, accuracy, and stability.

Probabilistic seismic slope stability analysis using swarm response surfaces and rotational Newmark sliding model with primary sliding direction

The paper develops an effective and efficient swarm response surfaces to locate the slip surface with minimum critical acceleration, based on which the rotational Newmark sliding displacement is calculated. The corresponding primary sliding direction is determined using the identical critical acceleration from rotational Newmark sliding model. The proposed method is validated against the full search where the slip surface with minimum critical acceleration is located by a large number of trials through a homogeneous soil slope and a spatially variable soil slope. The comparative results have demonstrated that the proposed swarm response surfaces act as an efficient surrogate model with only 0.1% of time effort compared with full search method. Although the critical slip surfaces determined using step-wise procedure and simultaneous procedure can lead to agreeable probability density functions (PDFs) of rotational Newmark sliding displacement D compared to the proposed method, the significant discrepancies in sliding area and primary sliding directions among the three methods have been observed even for homogeneous soil slope. The variations of critical slip surfaces, the sliding area A and primary sliding direction αm should be properly accounted for in seismic slope risk assessment using the swarm response surfaces.

Influence of soft band on seismic slope stability by finite-element limit-analysis modelling

Soft bands may widely exist in sites, and their presence complicates the analysis of slope stability, particularly when the limit analysis method is adopted. Note that the use of the limit analysis method is capable of providing rigorous lower and upper bound solutions and hence is widely used in soil slope stability analyses. To account for soft band effects, finite-element lower-bound (FELB) and finite-element upper-bound (FEUB) approaches are introduced in this study. Finite element discretization aids in the construction of a statically allowable stress field and kinematically admissible velocity field, which are prerequisites for limit analysis. In combination with a modified pseudodynamic approach, seismic slope stability analysis is evaluated through linear programming. Lower and upper bound solutions of the slope safety factor (FoS) are optimized with an interior point algorithm, which aids in better estimating the true FoS of seismic slope stability. The nonassociated flow rule is also discussed herein. After validating the upper and lower linear programming models by limit equilibrium and FEM, the soft band’s effects on seismic slope stability are discussed, and a rotational-translational failure mechanism is revealed by critical velocity fields. A less than 5.1% difference between lower- and upper-bound solutions is favourable for providing a reliable reference for slope design.

Seismic stability analysis of heterogeneous slopes reinforced by inclined soil nails

This study aims to propose an effective approach to evaluate the seismic stability of heterogeneous slopes reinforced by inclined soil nails. The modified pseudo dynamic approach is applied to properly describe the characteristics of seismic loads with time and space. The discretization-based failure mechanism generated from the slope crest is divided horizontally into many blocks to incorporate the heterogeneous soil properties and depth-dependent seismic accelerations into the analysis of the stability issue. The critical seismic acceleration coefficient is then determined to assess the slope stability using the kinematic approach of limit analysis. The proposed method is validated by comparisons with existing solutions and numerical results for some available cases. A systematic parametric analysis is conducted to discuss the effects of model parameters on the slope stability. Results show that there exist optimal relative nail lengths and optimal incline angles of soil nails to obtain the maximum critical seismic acceleration coefficient for reinforced slopes. Finally, an application of the proposed model to spatially variable soil strength properties is performed to illustrate that the proposed method has the potential to serve as a benchmark for the slope stability under complex geological conditions.

Seismic Stability Analysis of Slopes Using a Pseudo-Dynamic Method Combined with an Upper Bound Method

Seismic Stability Analysis of Slopes Using a Pseudo-Dynamic Method Combined with an Upper Bound Method

Correlations between factor of safety with distributed load and crest length – Zariwam landslide as case study

ABSTRACT This paper examines the impact on Factor of Safety (FS) value due to the variation in distributed load (LD), Crest length (CL), shear strength (τ), and shear stress (σ) both in seismic and non-seismic conditions. The main purpose of this paper is to develop correlations between these parameters, which can be used in any slope stability analysis design project. Forty number of analyses are performed by considering different soil material properties. Slope stability analysis is performed using Slide software and correlations are developed using Statistical Package for Social Sciences (SPSS) software as well as with the help of Microsoft Excel. The analysis results indicate that the seismic slope stability analysis gives optimum value for slope FS and therefore it is highly recommended to perform and give preference to seismic slope stability analysis of any soil slope to compute and recommend FS value. The main novelty of this paper are the eight new correlations. These correlations can be used in slope stability projects like earthfill dams design, embankments, or any slope design project or case study to know about the slope factor of safety in detail.

Insights into seismic slope deformation patterns using finite element analysis

Two-dimensional (2D), nonlinear total stress finite-element analyses were performed to investigate the seismic deformation patterns for soil slopes. The numerical parametric analyses consisted of 16 models with soil stiffness and strength parameters selected to isolate the impact of yield acceleration, depth of the sliding mass, natural period of the slope, and the slope angle on the deformation patterns. The results indicate that deeper sliding masses experience notable strain localization at the sliding mass depth, while shallow sliding masses experience more distributed straining throughout the entire soil mass. These factors result in larger displacements for the deep sliding masses relative to shallow sliding masses at small ky, whereas shallow sliding masses experience larger movements at large ky. The numerical simulations also show that an increase in shear wave velocity or decrease in slope height result in smaller displacements, although the effect of shear wave velocity is more significant. Importantly, the slope angle notably affects the resulting displacements and when ky is the same. A steeper slope increases displacements for deep sliding masses but reduces the movements for shallow sliding masses. The deformation patterns in the finite element simulations are inconsistent with the sliding block assumptions commonly employed in seismic slope stability analysis and point to the need to develop empirical slope displacement models from finite element simulations. However, this study shows that to capture fully the factors that affect seismic slope displacement the numerical models analyzed must consider a comprehensive set of slope models that vary the depth of the sliding mass, the shear wave velocity, the slope height, and the slope angle in addition to the yield acceleration.

In-situ investigation on coal mine overburden dump slope and its seismic stability considering heterogeneity

Stability of the coal mine overburden (OB) dump slopes is many times compromised owing to the lesser availability of the in-situ characteristics of the OB dump materials and their spatial heterogeneity. In this study, multi-channel analysis of surface waves (MASW) investigation was carried out for the characterization of OB dump materials of Jambad opencast coal mine of India and the variation of heterogeneous in-situ characteristics has been reported in terms of statistical parameters. Next, the stability of a two-bench OB dump slope against seismic forces was investigated through finite element limit analyses coupled with random field theory utilizing Karhunen-Loeve expansion method for the spatial heterogeneity of the OB dump material. The effects of spatial heterogeneity of the OB dump material on the probability of failure and the critical pseudostatic seismic coefficient of the slope were investigated through Monte-Carlo simulations. The influence of spatial heterogeneity of OB dump materials were investigated with both isotropic and anisotropic correlation lengths. Finally, seismic slope stability analyses were also carried out using the discrete element method for the size heterogeneity of the OB dump materials. This study summarizes the effects of heterogeneity of material property and size on the seismic stability of OB dump slope.

Centrifuge modeling and analytical validation of seismic amplification in a slope during earthquakes – Implications to seismic slope stability analysis

Earthquake-induced slope failure causes enormous damage to structures above and below the slope. The acceleration amplified within the slope directly degrades the stability of the slope. However, the seismic amplification characteristics within a slope during earthquakes remains poorly identified. This study explores seismic amplification of a slope during earthquakes through dynamic centrifuge tests. Comparison of the acceleration amplification patterns between a slope model and a flat ground model revealed that the acceleration was concentrated at the crest and near the slope surface. This phenomenon was verified through the analytical model developed based on a multi-degree of freedom mass-damper-spring system. In addition, the analytical model enabled the computation of the peak acceleration at each part of the slope and allowed examination of the factor of safety for slope stability. While various locations within a slope can be chosen to determine the representative acceleration as well as the free-field flat ground response, the use of the acceleration at the crest resulted in the lowest factor of safety value. Therefore, a conservative analysis would preferably use the accelerations at the crest and on the slope surface, rather than using the accelerations in a free-field flat ground. This study presents unique ground acceleration data from the well-controlled physical modeling of a slope and a simple but robust analytical model to predict seismic amplification in a slope, which provides better insight into determination of ground acceleration for slope stability analysis.

Effect of Excitation-Applied Manners on Permanent Displacements of Planar Slopes Using Dynamic Sliding Blocks Analysis

The sliding block model is widely used to evaluate the stability of slopes under earthquakes. In this model, the horizontal ground motion is usually applied to the parallel to the slope, whereas the vertical ground motion is commonly ignored. This study investigated the effects of different excitation-applied methods (EAMs) on slope permanent displacements (PDs) using a general sliding block model. For this purpose, three types of ground motion records selected from the NGA-West2 database were applied with six different EAMs to a series of gentle/steep slope sliding systems whose critical accelerations ac ranges from 0.01 to 0.40g. Comparison of the PDs obtained from the two-dimensional (2D) EAM and the other five systems reveal the following: (1) the common practice of applying a one-dimensional (1D) input motion excessively underestimates the PDs of sliding systems, particularly for those with large slope angles and large critical accelerations; and (2) the effects of the vertical component on the arithmetic mean of PDs are ignorable although the impact can reach several times for some cases in which the slopes are located in near-fault areas and affected by pulse-like ground motions. Besides, it is demonstrated in this study that applying the horizontal and vertical base motions simultaneously to the slope can be the most suitable excitation-applied manner for seismic slope stability analysis in the near-fault zone.

A Pseudo-dynamic Approach for Seismic Stability Analysis of Rock Slopes in Hoek–Brown Media

A Pseudo-dynamic Approach for Seismic Stability Analysis of Rock Slopes in Hoek–Brown Media

Seismic Analysis of Earth Slope Using a Novel Sequential Hybrid Optimization Algorithm

One of the most important topics in geotechnical engineering is seismic analysis of the earth slope. In this study, a pseudo-static limit equilibrium approach is applied for the slope stability evaluation under earthquake loading based on the Morgenstern–Price method for the general shape of the slip surface. In this approach, the minimum factor of safety corresponding to the critical failure surface should be investigated and it is a complex optimization problem. This paper proposed an effective sequential hybrid optimization algorithm based on the tunicate swarm algorithm (TSA) and pattern search (PS) for seismic slope stability analysis. The proposed method employs the global search ability of TSA and the local search ability of PS. The performance of the new CTSA-PS algorithm is investigated using a set of benchmark test functions and the results are compared with the standard TSA and some other methods from the literature. In addition, two case studies from the literature are considered to evaluate the efficiency of the proposed CTSA-PS for seismic slope stability analysis. The numerical investigations show that the new approach may provide better optimal solutions and outperform previous methods.

Internal stability analysis of geocell-reinforced slopes subjected to seismic loading based on pseudo-static approach

Seismic stability analysis of geocell-reinforced slopes (GRSs), considering shear and moment strength in addition to tensile resistance for geocells, is a novel topic for which scarce studies are found in the literature. Despite few available studies, an analytical approach is presented in this study to investigate the seismic internal stability of GRSs, employing the pseudo-static method based on a limit state approach. Results are given in terms of conventional design charts representing the required total strength and critical length of geocells. The results show that with increasing the horizontal seismic acceleration (kh), the internal stability degenerates since the required strength and critical length of geocells increase. For GRSs subjected to greater kh, the effect of increasing the vertical seismic component (kv) on increasing the required strength and length of geocells is more considerable than those subjected to lower kh values. Parametric analyses are conducted, under various seismic conditions, to investigate the effect of increasing the geocell height and raising the number of geocell layers, leading to the reduction in the required strength and length of geocells. Such effects are found to be dependent on the parameters such as the intensity of seismic excitation, material properties and geometry of slope.

Efficient Seismic Stability Analysis of Embankment Slopes Subjected to Water Level Changes Using Gradient Boosting Algorithms

Embankments are widespread throughout the world and their safety under seismic conditions is a primary concern in the geotechnical engineering community since the failure events may lead to disastrous consequences. This study proposes an efficient seismic slope stability analysis approach by introducing advanced gradient boosting algorithms, namely Categorical Boosting (CatBoost), Light Gradient Boosting Machine (LightGBM), and Extreme Gradient Boosting (XGBoost). A database consisting of 600 datasets is prepared for model calibration and evaluation, where the factor of safety (FS) is regarded as the output and four influential factors are selected as the inputs. For each dataset, the FS corresponding to the four inputs is evaluated using the commercial geotechnical software of Slide2. As an illustration, the proposed approach is applied to the seismic stability analysis of a hypothetical embankment example subjected to water level changes. For comparison, the predictive performance of CatBoost, LightGBM, and XGBoost is investigated. Moreover, the Shapley additive explanations (SHAP) method is used in this study to explore the relative importance of the four features. Results show that all the three gradient boosting algorithms (i.e., CatBoost, LightGBM, and XGBoost) perform well in the prediction of FS for both the training dataset and testing dataset. Among the four influencing factors, the friction angle φ is the most important feature variable, followed by horizontal seismic coefficient Kh, cohesion c, and saturated permeability ks.

Seismic stability analysis of two-stage slopes reinforced with one row of piles

Seismic stability of a two-stage soil slope reinforced by one row of piles is analyzed using the upper bound theorem combined with pseudo-static method considering the pile axial force. For a specified safety factor of the piled slope, explicit expression of the required pile shear resistance is derived, in which the effect of axial force of the piles on the potential slide mass omitted in most of previous studies is reasonably introduced. Analysis results of examples show that the pile shear resistance and potential slip surface by the proposed method are in good agreement with those by numerical simulation. The pile reinforcement effect on the slope is operational under smaller seismic conditions, whereas it is limited and not significant with the increase of the seismic excitations. The pile shear resistance and range of the critical slide mass increase with the horizontal seismic acceleration coefficient. Compared with the existing results omitting the pile axial force, more conservative upper bound solutions of the pile shear resistance are obtained by the proposed method, especially under higher design safety factor and seismic loads. Widening the bench and constructing the pile row near the slope crest are conducive to practicably optimize the reinforcement effect on the two-stage slope under seismic excitations.

MODIFIED NEWMARK APPROACH FOR EVALUATION OF EARTHQUAKE–INDUCED DISPLACEMENT OF EARTH DAM- APPLYING FOR RE-DIVISION OF SLIDING MASS

The conventional Newmark sliding block approach for evaluating the earthquake-induced displacement of earth dams is widely used in practice. However, the change in the position of the sliding mass with time when a slip occurs is not taken into account in the conventional Newmark approach when calculating the seismic displacement during an earthquake. Thus, a modified Newmark analysis is presented here in order to consider the influence of the changing position of the sliding mass on the estimated seismic displacement of an earth dam by re-dividing the sliding mass. A comparison of the results of the conventional and the modified Newmark approaches shows that ignoring the change in the sliding mass position over time can lead to the overestimation of the sliding displacement, especially if the Fellenius method, a less rigorous method, is used for evaluating the yield seismic intensity. In this study, the modified Newmark approach, using a relatively easy method among strict methods (simplified Bishop method), leads to a more realistic assessment of the permanent displacement in seismic slope stability analyses.

Under and post-construction probabilistic static and seismic slope stability analysis of Barmshour Landfill, Shiraz City, Iran

Under and post-construction probabilistic static and seismic slope stability analysis of Barmshour Landfill, Shiraz City, Iran

Seismic stability analysis of slopes with cracks in unsaturated soils using pseudo-dynamic approach

In practice, soil slopes are commonly unsaturated and may suffer from the adverse effects of earthquakes. Stability assessment of slopes subjected to earthquakes tends to consider whether the soils are dry or saturated while neglecting the time and spatial effects of seismic waves; in such assessments, the actual features cannot be reflected sufficiently. In the present study, a framework considering unsaturated soils was developed to investigate the seismic stability of slopes accounting for tension cracks using the pseudo-dynamic approach. Several expressions for apparent cohesion were applied to analyze the influence of matric suction, and seepage under different phreatic levels was also included. The pseudo-dynamic approach was applied to characterize the time and spatial effects of earthquakes. Two types of cracks, open cracks (cracks existing prior to slope failure) and formation cracks (cracks forming as part of a slope failure mechanism), were considered. A closed-form solution for the critical height of the slopes was derived from the energy balance equation of the Limit Analysis upper bound method, and the safety factor was obtained. The validity of this approach was verified by comparison with published solutions. Through the parametric analysis, it was found that higher amplification factors and seismic coefficients led to a smaller discrepancy in the safety factor between the slopes with open cracks and formation cracks, yet a reverse trend was observed at a higher value of matric suction. The effect of matric suction on slope stability was more apparent with a lower water level. Different shear strength models of unsaturated soils led to different safety factors.