Sliding Block Approach Research Articles

Regional earthquake-induced landslide assessments for use in seismic risk analyses of distributed gas infrastructure systems

Earthquake-induced landslides are associated with significant risks to human lives and infrastructure. Spatially distributed infrastructure systems, such as pipelines, power lines, and transportation networks, are at particular risk to seismic landslides due to their large spatial extent. To conduct a comprehensive seismic landslide risk assessment for these systems, there is the need to evaluate the seismic landslide characteristics (i.e., location, size, displacement, direction) on a broad, regional scale. This paper presents a framework for seismic landslide analysis that provides this information for subsequent risk assessments. The approach computes seismic landslide displacements using a sliding block approach while accounting for the uncertainties in the input variables and displacement models using a logic tree. The computed displacements are then aggregated based on geomorphic landforms to define landslide zones. For each landslide zone, the statistical distributions of landslide features, such as landslide size, displacement level, and direction of movement, are defined. These attributes are presented in a format that can be integrated with fragility models for distributed infrastructure systems to quantify risk on a regional scale. The application of the approach is demonstrated through assessments for gas pipeline networks across the state of California in the United States.

Centrifuge and theoretical study of the seismic response of anchored steel sheet pile walls in dry sand

Displacement-based approaches have been proven to be effective for the seismic design of gravity retaining structures. However, application of these methods to embedded flexible walls, such as anchored steel sheet pile (ASSP) walls, is still an open issue, as the factors affecting the accumulation of permanent displacements of these systems are not fully understood. This paper presents the results of four dynamic centrifuge tests on small-scale models of ASSP walls in uniform dry sand. The experimental results showed that ASSP walls can experience different failure mechanisms depending on their geometry and on the magnitude of accumulated displacements. During the earthquake, the system exhibits an overall increase of its seismic capacity, caused by: (a) progressive mobilisation of the soil passive strength; (b) sand densification; (c) rotation of the walls; and (d) reduction of the retained height. Accounting for these effects in pseudo-static limit equilibrium solutions improved the predictions of both the critical failure mechanism and the maximum internal forces in the structural members. Moreover, it allowed development of an efficient analytical tool for the prediction of the seismic permanent displacements of these systems, based on Newmark's sliding block approach.

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.

Prediction of earthquake-induced permanent deformations for concrete-faced rockfill dams

Prior studies highlight the importance of earthquake-induced permanent displacement for the safety assessment of the embankment dams. Concrete-faced rockfill dams (CFRDs) have become popular at especially seismically active regions with their high seismic energy absorption capacity. However, seriously damaged rockfill dams have been reported after some earthquake exposures. Even so researchers have focused on the dynamic response of embankments, few studies have been conducted to reveal the seismic behavior of rockfill dams. In this study, the issue under scrutiny is to establish a preliminary design procedure considering the earthquake-induced permanent displacement and acceleration response of CFRDs. For this purpose, numerical models are prepared with various geometric and material properties. Real earthquake records are used for seismic excitation. Dynamic analyses are conducted with a finite element method-based software. The equivalent linear analysis procedure is followed under two-dimensional plain-strain condition. Acceleration responses of dams are recorded at the centerline of the models. Then, the Newmark’s sliding block approach is utilized to calculate the permanent displacements from acceleration records. A procedure is developed for the engineers to foresee the likely permanent displacement at the preliminary design stage. To prove the reliability, the recommended procedure is applied to case histories, and then the results are compared.

Effect of vertical seismic coefficient on cohesive-frictional soil slope under generalised seismic conditions

ABSTRACT In the present work, seismic performance parameters have been reviewed by considering the possible combined action of vertical and horizontal seismic loadings of the ground motion during the earthquakes. Analytical expressions of factor of safety, yield seismic coefficient and permanent seismic displacement of a cohesive-frictional soil slope have been developed by following deterministic sliding block approach in a two-dimensional pseudo-static framework. The slope with a planar failure surface is assumed to follow the Mohr-Coulomb criterion by considering a slice of unit thickness through the slope. For a given range of slope geometrical and soil parameters, the role of vertical seismic coefficient has been analysed in the presence of cohesion to investigate its effect on factor of safety, yield seismic coefficient, and consequently on the permanent seismic displacement of the slope through a set of graphical presentations. The results show that avoidance of vertical seismic component of the ground motion in the stability analysis may lead to severe slope failures. The general expressions proposed herein can be used to carry out a quantitative stability assessment of cohesive- frictional soil slopes during earthquakes in real-life projects.

Spatial distribution of yield accelerations and permanent displacements: A diagnostic tool for assessing seismic slope stability

Seismically-induced permanent displacements of slopes are commonly evaluated using the Newmark sliding block approach. The conventional Newmark approach, while convenient in application, is often applied to a singular potential failure mechanism, omits consideration of the spatial distribution of potential failure mechanisms, neglects complex yet realistic failure geometry, and does not consider the temporal evolution of the critical mechanism. The proposed diagnostic tool applies the Newmark approach within a rigorous limit equilibrium framework to produce spatial distributions of yield accelerations and seismically-induced permanent displacements, or yield maps and surface-associated displacement maps, respectively. In this study, the application and utility of these diagnostic tools are demonstrated through a sensitivity analysis considering various soil strength parameters, horizontal and vertical motions, and complex slope and failure geometries. Additionally, it is shown that the proposed diagnostic tool reasonably estimates post-seismic geometry, shown by a comparison to an experimental shake table study. Using yield and displacement maps, both coseismic displacement and the range of potentially unstable geometry may be constrained. Moreover, the spatial and temporal evolution of possible seismically-induced displacements may be considered. This tool provides a rational means of applying sliding block approaches that reduces the need to assume the surface of maximum displacement a priori while retaining the simplicity that has facilitated the application of the sliding block approach versus more complex numerical models. The proposed diagnostic tools also provide a framework for future potential analyses, as it can be modified to incorporate other slope stability methods or seismic analyses.

DEM simulations of the seismic response of granular slopes

In this study, a three-dimensional microscale framework utilizing the discrete element method (DEM) is used to examine the seismic response of dry granular slopes under different conditions of ground motions. The presented model inherently accounts for soil nonlinearity and damping in response to shear deformations. The essential characteristics of wave propagation including motion amplification and resonance were observed from the computational results. The impact of the amplitude and the frequency of the input motion on the response of the slope was examined. Comparisons are made between results from DEM simulations and results from existing methods that utilize the Newmark sliding block approach. Generally, these methods predict sliding displacements less than those computed using DEM.

Analytical expressions for determining the stability of cohesionless soil slope under generalized seismic conditions

In recent major earthquakes, the researchers have found the need for consideration of vertical seismic acceleration for the stability analysis of the man-made and natural slopes. However, in most past studies, the performance of slopes has been assessed by accounting only the horizontal seismic component of the ground motion, without giving due weightage to the effect of vertical component. In the present study, analytical expressions are derived to determine the factor of safety, yield seismic coefficient and consequently the seismic displacement of cohesionless soil slope under combined horizontal and vertical components of the ground motion. The derivation uses the Newmark’s sliding block approach, in which the soil slope with a planar failure surface within the framework of conventional pseudo-static analysis is assumed to follow the Mohr-Coulomb failure criterion. The effects of vertical seismic coefficient on the stability of cohesionless slope have been studied through a set of graphical presentations for a specific range of soil parameters. It is observed that overlooking the effect of the vertical component of the ground motion on factor of safety and the displacement while designing the slope may be detrimental, resulting in the slope failure. The general expressions presented in this paper may be highly useful in the field of earthquake geotechnical engineering practice for designing the cohesionless soil slopes under combined horizontal and vertical seismic loads.

A Modified Newmark Methodology for Permanent Deformation Analysis of Rock-Fill Dams

Newmark sliding block approach has been extensively studied by many researchers in the past decades. Significant progress has been made to alleviate its deficiencies and overcome its simplifying assumptions, but some aspects such as the cyclic shear strength and time history vertical acceleration in the Newmark sliding displacement analysis are seldom considered strictly. In the presented research, a modified Newmark methodology for sliding deformation analysis of rock-fill dams subjected to strong earthquake is proposed. In order to make the seismic safety evaluation of dams more realistic, the influence of cyclic shear strength (earthquake-induced reduction of shear strength) and time history vertical acceleration obtained from the dynamic response analysis on the critical acceleration and accumulative sliding displacement of the flexible sliding body is considered. Detailed comparison between the proposed method and existing methods is performed via the analysis of two typical dams, that is, a virtual rock-fill dam with a height of 100 m which is assumed to be situated on rock formation and a real core rock-fill dam with a height of 150 m built on deep overburden layers. It is demonstrated that the cyclic shear strength and time history vertical acceleration within flexible sliding body, as highlighted in the proposed method, have significant effect on the seismic safety evaluation, critical acceleration, and accumulation of sliding deformation of rock-fill dams subjected to strong earthquake loading. The existing approaches tend to provide unconservative evaluation on the consequences of earthquakes on rock-fill dams.

Nested Newmark model to calculate the post-earthquake profile of slopes

The Newmark sliding block approach is a common means of evaluating permanent displacements of slopes undergoing seismic loading. However, the conventional Newmark approach omits the presence of multiple shear zones or regions of dispersed shear movement. The occurrence of these shear movements within slopes can often materialize with added vertical and lateral movements above the basal failure surface typically considered in the conventional Newmark approach. This study modifies the conventional Newmark sliding block approach by discretizing a given slope into a series of nested, critical failure wedges, each with an associated yield acceleration, termed a Nested Newmark Model (NNM). Use of the NNM enables assessment of a post-earthquake slope profile within a limit equilibrium framework based on the integration of relative displacements from the toe to the crest. The results demonstrate a different response than conventional Newmark approaches. The model outputs can account for the restriction of toe movements as well as heaving and slumping behavior of the slope face and crest, respectively. Larger seismic excitation resulted in further destabilization of nested wedges near the crest. The presented approach establishes a framework that can be extended to any type of failure geometry or series of failures, including rotational geometry. These results are compared to a numerical model, which exhibit similar behavior. This framework is conceptual, but builds upon the well-accepted Newmark sliding block approach to provide an alternative means of assessing post-earthquake slope movements.

Newmark sliding block model for predicting the seismic performance of vegetated slopes

This paper presents a simplified procedure for predicting the seismic slip of a vegetated slope. This is important for more precise estimation of the hazard associated with seismic landslip of naturally vegetated slopes, and also as a design tool for determining performance improvement when planting is to be used as a protective measure. The analysis procedure consists of two main components. Firstly, Discontinuity Layout Optimisation (DLO) analysis is used to determine the critical seismic slope failure mechanism and estimate the corresponding yield acceleration of a given slope. In DLO analysis, a modified rigid perfectly plastic (Mohr–Coulomb) model is employed to approximate small permanent deformations which may accrue in non-associative materials when subjected to ground motions with relatively low peak ground acceleration. The contribution of the vegetation to enhancing the yield acceleration is obtained via subtraction of the fallow slope yield acceleration. The second stage of the analysis incorporates the vegetation contribution to the slope's yield acceleration from DLO into modified limit equilibrium equations to further account for the geometric hardening of the slope under increasing soil movement. Thereby, the method can predict the permanent settlement at the crest of the slope via a slip-dependent Newmark sliding block approach. This procedure is validated against a series of centrifuge tests to be highly effective for both fallow and vegetated slopes and is subsequently used to provide further insights into the stabilising mechanisms controlling the seismic behaviour of vegetated slopes.

The Effect of the Vertical Acceleration on Stability Assessment of Seismically Loaded Earth Dams

Abstract In the assessment of slope stability, the vertical component of acceleration is commonly neglected. However, signal analyses performed on a large number of acceleration time histories have revealed that the vertical peak ground acceleration can be as high as the horizontal one. In this paper, a method of slope stability analysis regarding the vertical component of acceleration is proposed. It considers a rigid body system affected by the acceleration time histories in both horizontal and vertical directions. In a general case, the strength of the contact between acceleration components is time dependent. Parametric analysis was performed on the basis of cyclic harmonic loading, assuming a safety criterion in the form of permanent displacement. The results, for both harmonic and real acceleration time histories, were compared with the results of the commonly used Newmark’s sliding block approach, which revealed significant differences in permanent displacements calculated by the two methods.

Aftershocks and the whole-life seismic performance of granular slopes

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block (‘Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the ‘damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.

Comprehensive procedure for earthquake site response analysis in an industrial region near Istanbul, Turkey

The paper presents ground motion analysis and earthquake safety criteria for a petroleum storage tank on a slope in the Marmara Region of Turkey. A probabilistic assessment of the earthquake hazard for 50 and 2 % probability of exceedance in 50 years was conducted. Ground motions (using stochastic Green’s function procedure) and stability of the present sliding surfaces were analysed numerically. Permanent displacements associated with a 7.4 magnitude earthquake were computed using the Newmark’s sliding block approach.

A strategy to address the task of seismic micro-zoning in landslide-prone areas

Abstract. As concerns landslide prevention and mitigation policies at the urban scale, the ability of Geographical Information Systems (GIS) to combine multi-layered information with high precision enables technicians and researchers to devote efforts in managing multiple hazards, such as seismically induced instability in urbanized areas. As a matter of fact, many villages in the Italian Apennines, placed near high-energy seismic sources, are characterized by active sliding that are seasonally remobilized by rainfall. GIS tools can be useful whether accurate Digital Elevation Models (DEM) are available and detailed mechanical and hydraulic characterization of superficial deposits over significant portion of the urban territory is undertaken. Moreover, the classic methods for estimating the seismic-induced permanent displacements within natural slopes are drawn from the generalization of Newmark's method. Such method can be applied to planar sliding mechanism that can be considered still valid wherever shallow landslides are generated by an earthquake. The failure mechanism depends on the mechanical properties of the superficial deposits. In this paper, the town of Castelfranci (Campania, southern Italy) has been studied. This small town, hosting two thousand inhabitants, suffers from the seasonal reactivation of landslides in clayey soil deposits due to rainfall. Furthermore, the site is seismically classified by means of the peak ground acceleration (PGA) equal to 0.246 g with respect to a 475 yr return period. Several studies on the evolution of slopes have been undertaken at Castelfranci and maps have been drawn at the urban scale not taking into any account the seismic hazard. This paper shows possible seismically induced hazard scenarios within the Castelfranci municipal territory aimed at microzonation of level 2, by estimating the slope permanent displacements comparable to those caused by the strongest historical seismic event that hit this area: the 1980 Irpinia earthquake. To this aim, geotechnical characterization of local soils collected over the last 25 yr by local technicians have been used to predict possible permanent displacements by means of Newmark's sliding block approach. Two simplified relationships relating peak ground acceleration and Arias intensity to permanent displacements have been used and compared. Although similar results are drawn, the two analyses point out the most hazardous sectors of the Castelfranci urban area.

A Simplified Feedforward Carrier Recovery Algorithm for Coherent Optical QAM System

A simplified quadrature amplitude modulation (QAM) feedforward carrier recovery algorithm is proposed. By introducing a new two-stage estimation structure and sliding-block approach, the required computational effort can be significantly reduced with a tolerable performance deterioration compared with the original algorithm. In order to choose the size of the sliding block properly, an analytical model is proposed that takes the optical SNR (OSNR) and the laser-linewidth-times symbol-rate product into account. The model reveals different influence of OSNR and the laser-linewidth-times symbol-rate product on the performance of any carrier recovery algorithm. The performance of the simplified algorithm is evaluated by Monte Carlo simulations for square 16-, 64-, and 256-QAM. The simulation results show that the computational effort for each symbol can be significantly reduced at the cost of a 11% reduction of laser linewidth tolerance.

Recent applications of sliding block theory to geotechnical design

The sliding block theory was proposed by Newmark for determining the permanent displacement of embankments and dams under earthquake loading. This paper highlights recent applications of sliding block theory to different geotechnical structures. The equations to determine seismic factor of safety, yield acceleration and permanent displacement are given for rock block, soil slope, landfill cover, geosynthetic-reinforced soil retaining wall, and composite breakwater. The presented equations for seismic stability degenerate to that of static stability in the absence of earthquake. The permanent displacement for various structures can be obtained from that of a horizontal sliding block through a correction factor. A simplified procedure is included for the permanent displacement under vertical acceleration. The sliding block approach is rational for design under high seismic load.

Improvement of stereo disparity estimation through balanced filtering: the sliding-block approach

In a typical disparity (or motion) estimation algorithm developed for interimage prediction, an interpolation of intensities is applied to one of the two images used. Therefore, nonfiltered intensities of the image being predicted are compared with low-pass-filtered intensities of the other image of the stereo pair. Consequently, noise and detail suppression in the two images are unequal. In this paper we propose to apply the same (balanced) filtering to both images. In addition to image smoothing that helps avoid unreliable intensity matches, a low-pass filter is used to carry out intensity interpolation at the same time; the computation of subpixel attributes is consistent with low-pass filtering of both images unlike arbitrary linear or cubic interpolation applied to one image only. The proposed approach lends itself naturally to a multiresolution implementation, We apply the new approach to stereo disparity estimation based on sliding blocks. Using synthetic and natural data we experimentally compare the new approach with the traditional sliding-block method. For standard stereoscopic images we demonstrate up to 2.4 dB reduction of disparity-compensated prediction error over the traditional sliding-block method.