Earthquake-induced Permanent Displacement Research Articles

An Improved Method for Estimating Earthquake-Induced Permanent Displacement of Bedding Rock Slopes

An Improved Method for Estimating Earthquake-Induced Permanent Displacement of Bedding Rock Slopes

Predictive model for seismic displacements of flexible sliding block subjected to near-fault pulse-like ground motions

A post investigation of landslides induced by strong earthquake events in recent years shows that near-fault pulse-like ground motions have a considerable impact on slopes. Accurate evaluation of the stability of slopes under near-fault earthquakes has become a crucial issue in seismic-prone areas. Permanent displacement is widely recognized as an effective index for evaluating the stability of slope. Based on the coupled analysis, an empirical earthquake-induced permanent displacement prediction model was developed. A displacement database of 318 pulse-like ground motions from 50 earthquake events was established. The proposed predictive model is a function of the maximum seismic coefficient-time history (kmax), maximum velocity coefficient of velocity-time history of the k-time history (kv-max), yield acceleration (ky), and period ratio (ratio of the natural period of the slope to the mean period of input motion, Ts/Tm). The dynamic responses (kmax and kv-max) are represented by two different functions. At small period ratios (Ts/Tm≤1.8), it is a function of peak ground acceleration (PGA), peak ground velocity (PGV) and ky. At large period ratios (Ts/Tm > 1.8), it is a function of PGV, Ts and ky. It successfully captured the velocity pulse and long period characteristics of pulse-like ground motions. Compared to the existing model, it is found that the model is more accurate when considering pulse-like ground motions. This prediction model can be used not only for the preliminary evaluation of slope stability but also for probabilistic seismic demand analysis of flexible slopes considering pulse-like ground motion in near-fault regions.

Analytical method for determining displacement and bending moment of embedded cantilever retaining walls subjected to pseudo-static earthquake accelerations

The performance of embedded cantilever retaining (ECR) walls, such as the diaphragm and sheet-pile walls, is measured by the permanent displacement they experience during an earthquake. In the conventional design methods, the embedment depth is derived by checking the wall's stability against a probable collapse mechanism and applying safety factors. Thereby, these methods are incapable of determining the wall displacement. The present study proposes an analytical method based on the pseudo-static approach for calculating the earthquake-induced permanent displacement of ECR walls in cohesionless soils. A displacement-dependent earth pressure mobilization relationship, where the earth pressure mobilization is a function of the wall displacement, is used to derive the passive resistance on the excavated side of the wall. With increasing earthquake acceleration, active soil pressure on the retained side of the wall increases and drives the wall towards the excavated side, which causes further mobilization of passive earth pressure; thus, the wall stability is maintained. In observations from past experimental studies, the required embedment depth is derived by assuming rigid rotation of the wall about a point near the wall base and balancing the forces and moments acting on the wall. Analytical expressions are provided for determining bending moment distribution along the wall height. The proposed results are compared with those of the available experimental and numerical studies, and they exhibit good agreement, which substantiates the validity of the proposed method. Parametric studies were performed to investigate the influence of soil friction angle, wall roughness, the magnitude of the horizontal and vertical earthquake accelerations on the wall displacement and internal forces of the wall.

Numerical Back-analysis of Caisson Quay Walls in the Yeong-il Bay Port during the 2017 Pohang Earthquake

The performance of nonlinear response history analysis was analyzed based on the historic case of the 2017 Pohang earthquake in Korea. The Yeong-il bay container terminal stopped operations for a period after the Pohang earthquake and intensive site and hazard investigations were conducted. Nonlinear response history analyses using various soil constitutive models, including sophisticated liquefaction models, were performed on the caisson quay wall under two-dimensional plane strain condition. The results of analysis were compared to the hazard investigation results. The analysis results exhibit reasonable agreement with the field measurement data for the earthquake-induced permanent displacement of the quay wall and quay crane rails.

Earthquake-Induced Permanent Displacements of Landslides in Himalaya Using Simplified Methods and Nonlinear FE Dynamic Analysis

Earthquake-Induced Permanent Displacements of Landslides in Himalaya Using Simplified Methods and Nonlinear FE Dynamic Analysis

Earthquake-induced permanent displacements of embedded cantilever retaining walls

Stability analysis of retaining walls in seismic areas is generally performed by calculating a safety factor against a possible mechanism of collapse. However, considering that limit conditions usually occur in some time intervals during an earthquake, a more rational approach consists in assessing the performance of the structure in terms of accumulated permanent displacements. In this context, a novel method is proposed in the present study for predicting the earthquake-induced permanent displacements of embedded cantilever retaining walls, such as diaphragm or sheet-pile walls. This method requires solving a simple motion equation of the structure subjected to the soil–structure contact stresses evaluated using a closed-form solution. Specifically, it is assumed that the wall undergoes a rigid rotation around a point located in its embedded portion. Comparisons are presented with both experimental and numerical results documented in published studies. In all cases considered, a satisfactory agreement is found between these results and those provided by the proposed method. In addition, the method accounts for some features of the seismic behaviour of embedded cantilever retaining structures observed during centrifuge tests. Summarising, the method is reliable, simple to use and requires few conventional parameters as input data. Therefore, it is suitable for routine applications.

A Dynamic Method to Predict the Earthquake-Triggered Sliding Displacement of Slopes

The earthquake-induced permanent displacement is an important index of the potential damage to a slope during an earthquake. The Newmark method assumes that a slope is a rigid-plastic body, and the seismic responses of sliding masses or seismic forces along the slide plane are ignored. The decoupled method considers no relative displacement across the sliding plane, so it overpredicts the seismic response of the sliding mass. Both dynamic and sliding analyses are performed in the coupled method, but when Ts/Tm is large, the results are unconservative. In this paper, a method is proposed to predict the earthquake-triggered sliding displacement of slopes. The proposed method is based on the Newmark rigid method, coupled method, and decoupled method considering both the forces at the sliding interface and the system dynamics under critical conditions. For the flexible system, the displacements are calculated with different stiffness values, and the results show that as the stiffness increases and tends to infinity, the critical acceleration and displacements of the proposed method are close to those of the Newmark method. The proposed method is also compared with the Newmark method with the period ratio Ts/Tm. At small values of Ts/Tm, the flexible system analysis results of the displacement are more conservative than those of the rigid block model; at larger values of Ts/Tm, the rigid block model is more conservative than the flexible system.

Effect of vertical input motion and excess pore pressures on the seismic performance of a zoned dam

This paper investigates the combined effect of the vertical component of the input motion and of the weakening effect associated to pore-pressure build-up with reference to a zoned earth dam for which the most recent probabilistic seismic hazard analyses promoted the need of evaluating its seismic performance.The two effects were studied through advanced plane-strain non-linear dynamic analyses using a finite-difference numerical model calibrated on an accurate geotechnical characterisation. The occurrence of ultimate limit states in the dam embankment is checked using sets of horizontal and vertical input motions properly selected to account for possible frequency coupling with the dam.The analysis results are presented and discussed in the paper focusing on (i) the main features of the plastic mechanisms temporarily induced by the seismic actions, (ii) the amplification of the horizontal and vertical accelerations acting in the dam body, (iii) the role of the energy and frequency content of the input motion on the magnitude of earthquake-induced permanent displacements, (iv) the combined effect of frequency coupling and non-linear soil behaviour on the overall dam response.

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.

Displacement hazard curves derived from slope-specific predictive models of earthquake-induced displacement

Probabilistic hazard curves for earthquake-induced permanent slope displacements incorporate the important variabilities associated with predictions of slope movements, such that a rational assessment of slope performance can be obtained. To date, displacements estimated from sliding block analyses predominantly have been used to compute displacement hazard curves, despite the fact that nonlinear finite element analysis is becoming the preferred method to evaluate the performance of slopes. This paper extends the probabilistic approach for use with displacements from finite element analyses. We develop slope-specific displacement prediction models using displacements computed by nonlinear finite element analyses. Various models are developed that utilize different ground motion intensity measures and each model is used to compute a displacement hazard curve for a site in Northern California. The computed hazard curves reveal that the different models generate a large range of epistemic uncertainty, and the model with the smallest standard deviation does not necessarily predict the smallest displacement hazard due to the influence of the shape of the ground motion hazard curve and of the displacement model. As a result, multiple displacement models that incorporate different intensity measures should be considered in any assessment of the seismic performance of slopes, in the same way that multiple ground motion models are incorporated into ground motion hazard analyses.

A simplified method for estimating Newmark displacements of mountain reservoirs

In the present article we propose a new simplified method for assessing the seismic performance of large mountain reservoirs. The pseudo-empirical regression model is established on the basis of decoupled dynamic analyses performed on 7 accelerograms applied to 33 structural and geotechnical configurations. We study the influence of embankment geometries and mechanical properties on the prediction of earthquake-induced permanent displacements estimated by Newmark analyses. We also discuss the relevance of our model by carrying out comparisons with existing simplified models and with post-seismic field observations on earth dams. A regression analysis using parameters of interest provides a pseudo-empirical predictive equation to carry out rapid, preliminary assessments of the seismic performance of mountain reservoirs.

Simplified Procedure for Coupled Seismic Sliding Movement of Slopes Using Displacement-Based Critical Acceleration

Downward movement of sliding soil mass in earthquake-induced earth slopes may gradually improve the system's stability. Hence, significant change in critical (or yield) acceleration of the slope is anticipated. The existing simplified coupled procedures, however, assume a constant critical acceleration in stick-slip sliding analysis. Fully coupled sliding block analyses with continuously increased critical acceleration were conducted to estimate earthquake-induced permanent displacement of earth slopes. The sliding mass was assumed as a flexible chain moving along the planes with gradually gentler inclinations. The measured data of a slope failure test in a shaking table were used to validate performance of the model. The proposed approach was compared with the previous procedures, which ignored critical acceleration changes due to downward movement of the sliding mass. Accordingly, earth slopes with smaller slip length were more influenced by the downward movement modification, especially in small amounts of initial yield acceleration. A semi-empirical equation is presented based on more than 425,000 modified-coupled analyses of several hundred strong ground motion records. An equation was then developed as a function of acceleration ratio, period ratio, slip length, peak ground velocity, Arias intensity, and earthquake magnitude. Predictions of the developed equation were compared with the available equations, which ignore the role of increased critical acceleration. It is shown that a majority of the previous models predict conservative estimates of seismic permanent displacements compared with that of new equation. The proposed semi-empirical model can be used as an alternative equation of seismic displacement for deterministic and probabilistic evaluations of earthquake-induced landslide hazard.

Prediction of seismic displacement of dry mountain slopes composed of a soft thin uniform layer

In this paper, the earthquake-induced permanent seismic displacement of dry mountain slopes is calculated from a series of two-dimensional dynamic nonlinear finite difference analyses. The mountain slopes considered are composed of a thin, soft, uniform soil layer underlain by an inclined bedrock parallel to the slope. The material properties of the soil, thickness of the soil layer, and slope inclination angles are varied. Equivalent acceleration time histories are calculated at potential sliding surfaces to derive amplification factors, and a Newmark sliding block analysis is used to calculate the seismic displacements. The calculated seismic displacements of the mountain slopes are compared with those predicted by empirical displacement models. The results show that mountain slopes composed of soft soil layers with a shear wave velocity less than or equal to 200m/s cannot be modeled as a rigid block because the displacement under strong ground motions will be greatly overestimated. The displacement prediction is significantly enhanced if the slope is modeled as a flexible sliding mass and the amplification characteristics are accounted for. A new flexible sliding block model, which uses multiple ground motion parameters, is shown to provide a reliable estimate of the sliding displacement. The success rate of the model to predict the landslide hazard category ranges from 52 to 88.3%.

Displacement-based seismic design of a shallow strip footing positioned near the edge of a rock slope

This paper presents a displacement-based dynamic design of shallow strip footings located close to the edge of homogeneous and isotropic rock slopes. The analysis is conducted using the “generalized tangential” technique in which the Hoek–Brown strength is replaced by an “optimal” tangential Mohr–Coulomb domain within the framework of the kinematic approach of limit analysis theory. In order to better understand the influence of these factors including geometrical features, rock strength parameters and seismic loading, a parametric study is carried out. An expression is derived and used to obtain a least upper bound solution for the bearing capacity of a footing on a rock slope considering a kinematically admissible log-spiral failure mechanism. In addition, a similar expression of the horizontal yield seismic coefficient is derived for a given load acting on the foundation.The assessment of earthquake-induced permanent displacement is performed by a simplified procedure. This requires the knowledge of a ground motion parameter that can be evaluated by site-specific seismic hazard analyses or ground motion prediction equations and that considers the actual sliding surface. The calculated displacement should not be greater than a selected limiting tolerable displacement for the specific case. An example is presented illustrating the application of the design procedure for the bridge foundations.

Seismic Bearing Capacity of Strip Footings Located Close to the Crest of Geosynthetic Reinforced Soil Structures

This paper investigates the performance of geo-reinforced soil structures subjected to loading applied to strip footings positioned close to a slope crest. The kinematic theorem of limit analysis, which is based on the upper bound theory of plasticity, is applied for evaluating the ultimate bearing capacity within the framework of pseudo-static approach to account for earthquake effects. The mechanism considered in this analysis is a logarithmic spiral failure surface, which is assumed to start at the edge of the loaded area far from the slope, consistent with the observed failure mechanisms shown in the experimental tests reported in the literature. A parametric study is then carried out to investigate the influence of various parameters including the geosynthetic configuration, backfill soil friction angle, footing distances from the crest of the slope, slope angles and horizontal seismic coefficients. Attention is paid to the failure mechanism because its maximum depth is the depth at least to which the reinforcements must be placed. Results of the analyses are presented in the form of non-dimensional design charts for practical use. Finally, a simple procedure based on the assessment of earthquake-induced permanent displacements is shown for the design of footing resting on reinforced slopes subjected to earthquake.

Displacement versus pseudo-static evaluation of the seismic performance of sliding retaining walls

Pseudo-static seismic analysis of retaining walls requires the selection of an equivalent seismic coefficient synthetically representing the effects of the transient seismic actions on the soil-wall system. In this paper, a rational criterion for the selection of the equivalent seismic coefficient is proposed with reference to sliding retaining walls. In the proposed approach earthquake-induced permanent displacements are assumed as a suitable parameter to assess the seismic performance and an alternative definition of the wall safety factor is introduced comparing expected and limit values of permanent displacements. Using a simplified displacement prediction model it is shown that, for a given design earthquake, reliable values of the equivalent seismic coefficient should depend on all the factors affecting the stability condition of the soil-wall system and on a threshold value of permanent displacement related to a given ultimate or serviceability limit state. To achieve a match between the results of the pseudo-static and of the displacement-based analysis, the proposed procedure detects the value of the equivalent seismic coefficient for which the two approaches provide the same factor of safety. Thus, without necessarily carrying out a displacement analysis, a measure of the safety condition of a soil-wall system consistent with the actual seismic performance may be achieved through an equivalent pseudo-static analysis.

Evaluation of tyre products as ground improving geomaterials

Applications of scrap tyre-derived recycled products (such as tyre chips and tyre shreds) in geotechnical engineering projects have been increasing largely because of their potential economic and environmental benefit. This paper first addresses and evaluates two novel Japanese experiences of tyre-derived recycled products in ground improvement applications. It then discusses and evaluates the deformation mechanism of such materials through non-destructive testing techniques. Direct shear testing procedures are first described, in which sand as well as layers of sand and tyre chips were examined to compare the deformation behaviour. The shear behaviour of the materials could be investigated through X-ray computed tomography (CT) during the testing. The particle image velocimetry (PIV) technique was then used to visualise the deformation properties. In addition, triaxial shear testing of tyre chips as well as tyre chip–sand mixtures is described, in which the compressibility and the deformation of the tyre chip particles were examined by X-ray CT scanning and PIV. Based on these test results, the mechanical properties and the internal structure during the deformation of tyre chips were finally evaluated for their applications as ground improving geomaterials. Model test results indicate that the presence of tyre chips (either as cushion or as reinforcing material) could substantially reduce the earthquake-induced permanent displacement of structures. Non-destructive test results indicate that the deformation characteristics of mixtures of tyre chips and sand are different from those of pure sand. Less shear strain is generated in tyre chips and tyre chips mixed with sand than that in pure sand, and the potential of onset of localisation diminishes with decreasing sand fraction. Also, it was found that tyre chips–sand mixtures do not undergo liquefaction if a suitable mixing percentage (sand fraction) is used. Therefore, tyre chips can be successfully used as a reinforcing material to help prevent the liquefaction of sandy soils.

Seismic Retrofit of Gravity Retaining Walls for Residential Fills Using Ground Anchors

Failure of several gravity retaining walls in residential areas built on reclaimed land, during the October 23, 2004 Chuetsu earthquake in Niigata Prefecture, Japan, determined the authorities to consider the seismic retrofit of the walls in order to mitigate future similar disasters in the urban environment. This study addresses the effectiveness of ground anchors in improving the seismic performance of such retaining structures through a sliding block analysis of the seismic response of an anchored gravity retaining wall supporting a dry homogeneous fill slope subject to horizontal ground shaking. Sliding failure along the base of the wall and translational failure along a planar slip surface of the active wedge within the fill material behind the wall were considered in the formulation, whereas the anchor load was taken as a line load acting on the face of the gravity retaining wall. The effects of magnitude and orientation of anchor load on the yield acceleration of the wall-backfill system and seismically induced wall displacements were examined. It was found that for the same anchor orientation, the yield acceleration increases in a quasi-linear manner with increasing the anchor load, whereas an anchor load of a given magnitude acting at various orientations produces essentially identical yield accelerations. On the other hand, the computed earthquake-induced permanent displacements of the anchored gravity retaining wall decrease exponentially with increasing magnitude of anchor load. Additionally, the influence of backfill strength properties (e.g., internal friction angle) on the seismic wall displacement appears to diminish considerably for the anchored gravity retaining wall. A dynamic displacement analysis conducted for the anchored gravity retaining wall subjected to various seismic waveforms scaled to the same peak earthquake acceleration revealed a good correlation between the calculated permanent wall displacements and the Arias intensity parameter characterizing the input accelerogram.

Seismic Response of a Composite Landfill Cover

The Olympic View Sanitary Landfill (OVSL) near Port Orchard, Washington, is a modern solid waste sanitary landfill covered, in part, by a composite cover system. The site was subjected to a free-field peak horizontal ground acceleration on the order of 0.16 g during the 28 February 2001 Moment Magnitude 6.8 Nisqually earthquake. To the knowledge of the writers, this is the first documented case history of a composite landfill cover shaken by strong ground motions. Postearthquake reconnaissance did not find any signs of earthquake-induced permanent displacement of the composite cover system. Accelerograms recorded within 1 km of the facility, the results of site-specific shear wave velocity measurements and laboratory interface shear testing, and these postearthquake observations provide a unique opportunity for a posteriori numerical analysis of this important case history. The seismic performance of the OVSL composite cover system was evaluated using four commonly used methods for seismic design of landfill cover systems. These methods include two simple screening procedures, a more rigorous screening procedure, and a decoupled equivalent-linear site response/Newmark-type permanent deformation analysis using the accelerograms recorded at the nearby strong motion station. The yield accelerations of the composite cover system, required for all four methods, were calculated using the results of construction quality assurance interface shear strength conformance testing. All four methods produce results consistent with the observed performance. However, the two simple screening procedures were significantly more conservative than the other two more rigorous methods.

One- and two-dimensional seismic analysis of solid-waste landfills

The results from one-dimensional (1D) and two-dimensional (2D) dynamic response analyses are compared to determine the reliability of the common practice of using 1D analysis to evaluate the seismic response of solid-waste landfills. Results indicate that 1D analysis generally provides a reasonably conservative estimate of the seismic loading and earthquake-induced permanent displacement for deep sliding surfaces, such as along the base liner. However, caution is warranted for shallower sliding surfaces, where 2D topographic amplification often results in larger values of seismic loading and permanent displacement than that predicted by 1D analysis. The 1D–2D analysis comparison is not just a function of geometry, but is also dependent on the different numerical formulations typically employed in each procedure (e.g., 1D wave propagation versus 2D finite element). Comparisons of accelerations along the landfill surface indicate that 1D analysis consistently under predicts the maximum horizontal acceleration (MHA) along the slope near the crest of the landfill. However, the seismic loading is shown to vary systematically with normalized cover slope length, with the maximum equivalent acceleration for the full cover slope being about 40% of the peak acceleration at the crest. Based on the results of this study, a simplified procedure is proposed for scaling 1D results to account for 2D topographic amplification and cover slope averaging when evaluating the seismic performance of landfill cover systems.Key words: solid-waste landfill, dynamic response, seismic loading, finite element analysis, Newmark sliding block analysis, damping.