JournalTOCs

Soil Dynamics and Earthquake Engineering

[8 followers] Follow
Full-text available via subscription

Subscription journal
ISSN (Print) 0267-7261
Published by Elsevier

[2556 journals]

Pile group response to liquefaction-induced lateral spreading: E-Defense large shake table test
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): Ramin Motamed , Ikuo Towhata , Tsuyoshi Honda , Kentaro Tabata , Akio Abe
  This paper presents the results of a large-scale shake table test at E-Defense facility on a pile group located adjacent to a gravity-type quay wall and were subjected to liquefaction-induced large ground displacements. Extensive liquefaction-induced large ground lateral spreading displaced the quay wall about 2.2m and damaged the pile foundation. The pile foundation consisted of a six-pile group which supported a footing and a superstructure model. Large lateral soil displacements were measured by several sensors such as inclinometers and the results favorably agreed with the directly observed deformations. Soil lateral displacement decreased as the distance from the quay wall increased landward. The piles were densely instrumented and the measured bending strain records were able to explain the damage to the piles. Lateral pressures of the liquefied soil exerted on the piles were measured using earth pressure (EP) sensors. The application of two design guidelines (JRA [1] and JSWA [2]) for estimation of liquefaction-induced lateral pressure on piles is discussed and their advantages and shortcomings are addressed. Furthermore, two simplified methods (Shamoto et al. [3] and Valsamis et al. [4]) are employed to predict the extent of liquefaction-induced large ground displacements and they are compared to the measured deformations. Finally, their accuracy for predicting the liquefaction-induced lateral displacements is evaluated and practical recommendations are made.
  
  PubDate: 2013-05-15T11:00:30Z
Ground response analysis of Kanpur soil along Indo-Gangetic Plains
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): R.B Jishnu , S.P. Naik , N.R. Patra , J.N. Malik
  The present work deals with 1D and 2D ground response analysis and liquefaction analysis of alluvial soil deposits from Kanpur region along Indo-Gangetic plains. Standard penetration tests and seismic down hole tests have been conducted at four locations namely IITK, Nankari village, Mandhana and Bithoor at 1.5m interval up to a depth of 30m below the ground surface to find the variation of penetration blows and the shear wave velocity along the depth. From the selected sites undisturbed as well as representative soil samples have been collected for detailed soil classification. The soil profiles from four sites have been considered for 1D and 2D ground response analysis by applying the free field motions of three Himalayan earthquakes namely Chamba earthquake (M w—5.1), Chamoli earthquake (M w—6.4) and Uttarkashi earthquake (M w—6.5). An average value of Peak Ground Acceleration (PGA) obtained from 1D and 2D analysis is considered for liquefaction analysis and post-liquefaction settlement. The excess pore water pressure ratio is greater than 0.8 at a depth of 24m from ground surface for IITK, Nankari village, Bithoor sites. More than 50% of post liquefaction settlement is contributed by layers from 21–30m for all sites. In general, the soil deposits in Kanpur region have silty sand and sand deposits and are prone to liquefaction hazards due to drastic decrease of cyclic resistance ratio (CRR) at four chosen sites in Kanpur.
  
  PubDate: 2013-05-15T11:00:30Z
Centrifuge and numerical modelling of ground-borne vibration from an underground tunnel
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): W. Yang , M.F.M. Hussein , A.M. Marshall
  Ground-borne vibration from underground tunnels is a major environmental concern in urban areas. Various studies, mostly based on numerical methods, have been conducted to investigate this problem. In the numerical models, soil stiffness and damping are commonly assumed to remain constant with depth (homogeneous assumption) in order to simplify the problem. However, various studies in the field of geotechnical engineering have shown that soil properties change with depth due to the effect of increased confining stress. This paper presents a study of the effects of variation of soil properties with depth (soil non-homogeneity) on ground-borne vibration from an underground tunnel. Both centrifuge and numerical modelling were used to perform the study. In the centrifuge model, a plastic pipe was buried within sand to model the underground tunnel. Vibration excitation was applied to the model tunnel invert by a small shaker. The tunnel and soil response was measured using accelerometers during the tests. Corresponding numerical models, based on FLAC 3D, were built to simulate the centrifuge tests. The potential boundary effects of the centrifuge tests were examined by the numerical models. The model responses for both homogenous and non-homogenous cases were also calculated by the numerical models. Comparison of the experimental and numerical results shows that a homogenous model can give acceptable estimates of the tunnel behaviour. However, a clear improvement of estimates of soil behaviour is observed when the variation of soil properties with depth is considered in the numerical model.
  
  PubDate: 2013-05-11T11:02:12Z
Ant colony optimization of tuned mass dampers for earthquake oscillations of high-rise structures including soil–structure interaction
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): Anooshiravan Farshidianfar , Saeed Soheili
  This paper investigates the optimized parameters for tuned mass dampers (TMDs) to decrease the earthquake vibrations of tall buildings; involving soil–structure interaction (SSI) effects. The time domain analysis based on Newmark method is employed in this study. To illustrate the results, Tabas and Kobe earthquakes data are applied to the model, and ant colony optimization (ACO) method is utilized to obtain the best parameters for TMD. The TMD mass, damping coefficient and spring stiffness are assumed as design variables, and the objective is to reduce both the maximum displacement and acceleration of stories. It is shown that how the ACO can be effectively applied to design the optimum TMD device. It is also indicated that the soil type greatly affects the TMD optimized parameters and the time response of structures. This study helps the researchers to better understanding of earthquake vibrations, and leads the designers to achieve the optimized TMD for high-rise buildings.
  
  PubDate: 2013-05-11T11:02:12Z
A note on plane-wave approximation
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): Hasan Faik Kara , Mihailo D. Trifunac
  It is shown that the plane-wave assumption for incident SH waves is a good approximation for cylindrical waves radiated from a finite source even when it is as close as twice the size of inhomogeneity. It is concluded that for out-of-plane SH waves the plane-wave approximation should be adequate for many earthquake engineering studies.
  
  PubDate: 2013-05-07T11:00:37Z
Editorial Board / Aims and Scope
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  PubDate: 2013-05-03T11:01:40Z
Feasibility of reducing three-dimensional wave energy by introducing periodic foundations
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Zhifei Shi , Jiankun Huang
  A new seismic isolation foundation called the periodic foundation is proposed, which can be described as a three-dimensional typical cell consisting of a high density core, a soft coating and a concrete matrix. Utilizing the attenuation zones (AZs) resulted by the periodicity of the foundation, the mechanism of this new seismic isolation system is different from the traditional ones. The seismic waves with the frequencies in the AZs cannot propagate across the foundation. Thus, the seismic responses on the top surface of the periodic foundation can be reduced significantly. In this paper, the dispersion curves of the three-dimensional three-component (3D–3C) periodic foundations are analyzed by the finite element method (FEM). The influencing factors such as physical and geometrical parameters of the typical cell are investigated. In order to verify its feasibility, a three-dimensional (3D) soil-foundation finite element model is analyzed, and the frequency zones of seismic attenuations are consistent with the AZs. The periodic foundation can greatly reduce the seismic response, which implies that the periodic foundation has a great potential application on seismic isolation.
  
  PubDate: 2013-04-25T11:00:30Z
Lumped-parameter model of foundations based on complex Chebyshev polynomial fraction
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Hai Wang , Weiqing Liu , Ding Zhou , Shuguang Wang , Dongsheng Du
  This paper uses the complex Chebyshev polynomials to develop the lumped-parameter (L-P) model of foundations. The method is an important extension to the approach adopting polynomials to model the dynamic properties of the foundation. Using the complex Chebyshev polynomials can reduce the unexpected wiggling in the foundation modeling, which inevitably occurs if using the simple polynomials of high degree. In the present analysis, the normalized flexibility function of foundation is expressed in terms of complex Chebyshev polynomial fraction. Through the partial-fraction expansion the complex Chebyshev polynomial fraction is decomposed into two sets of basic discrete-element models. The parameters in the models are obtained through the least-square curve-fitting to the available analytical or on-site measurement results. The accuracy and validity of the L-P model is validated through the applications to the surface circular foundations, embedded square foundations and pile group foundations, respectively. It is shown that in general the present model has better accuracy and needs fewer parameters than the existing L-P models.
  Highlights ► A lumped-parameter model based on complex Chebyshev polynomial fraction is developed. ► The present model can avoid the unexpected wiggling in foundation modeling. ► Excellent approximation is obtained by using fewer parameters. ► The method has a wide applicability.
  
  PubDate: 2013-04-21T11:00:32Z
Mesh grading approach for wave propagation in high velocity-contrast media
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Tielin Liu , Yu Luan
  A mesh grading approach based on investigated lump method has been presented for simulating wave propagation in high velocity-contrast media. Unstructured fine grids are used to discretize the low wave-velocity medium in order to ensure the accuracy of numerical computation, and unstructured coarse grids are used for the high wave-velocity medium in order to substantially reduce the computational cost. On the interface, one coarse grid can match the fine grids of arbitrary odd number. The key feature of the proposed method is the constructions of investigated lumps on the interfaces of media. The transition zone, which is commonly used in the discontinuous grid scheme based on the staggered-grid finite-difference method, will not be used any more. Moreover, the computational instability that the discontinuous grid schemes frequently encountered does not arise in the proposed method. The comparisons with the analytical solutions and the application in studying the effects of sedimentary basin demonstrated that the mesh grading approach is a valid, accurate, convenient and flexible algorithm in simulating wave propagations in high velocity-contrast media with irregular interfaces.
  
  PubDate: 2013-04-21T11:00:32Z
Compressional and shear wave intrinsic attenuation and velocity in partially saturated soils
- Abstract: Publication date: August 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 51
  Author(s): Hasan Ghasemzadeh , Amir Ali Abounouri
  A model for studying the propagation of compressional and shear waves in partially saturated soils is presented. The pores are filled with two immiscible fluids and the existence of four different wave modes including three compressional waves and one shear wave is demonstrated. The novel feature of the model is the consideration of tortuosity of fluid phases which are dependent on matric suction. The dispersion relations derived from the presented model are incorporated to study the influence of fluid saturation degree and frequency on the velocity and intrinsic attenuation of shear and compressional waves. Numerical simulations are performed on sand containing air–water mixture.
  
  PubDate: 2013-04-21T11:00:32Z
Contribution of ambient vibration recordings (free-field and buildings) for post-seismic analysis: The case of the Mw 7.3 Martinique (French Lesser Antilles) earthquake, November 29, 2007
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): J. Régnier , C. Michel , E. Bertrand , P. Guéguen
  Following the Mw 7.3 Martinique earthquake, November 29th, 2007, a post-seismic survey was conducted by the Bureau Central Sismologique Français (BCSF) for macroseismic intensities assessment. In addition to the inventories, ambient vibration recordings were performed close to the particularly damaged zones in the free-field and the buildings. The objective of the paper is to show the relevancy of performing ambient vibration recordings for post-earthquake surveys. The analyses of the recordings aim at explaining the variability of the damages through site effects, structure vulnerability or resonance phenomena and to help the characterization of the post-seismic building integrity. In three sites prone to site effects, we suspect damage to be related to a concordance between soil fundamental frequency and building resonance frequency. Besides, the recordings of ambient vibrations at La Trinité hospital before and after the earthquake allow us to quantify the damage due to earthquake in terms of stiffness loss.
  
  PubDate: 2013-04-17T11:00:48Z
Evaluation of blast-induced ground vibration effects in a new residential zone
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Onur Dogan , Özgür Anil , Sami O. Akbas , Erkan Kantar , R. Tuğrul Erdem
  The results from an experimental blasting program that was performed at the special explosives training field of the General Directorate of Security in Ankara, where new residential blocks are planned to be constructed nearby, are presented. With the objective of estimating the blast-induced ground vibration effects on the proposed structures, various blasting parameters of nineteen surface and underground explosions were recorded in two directions at three measurement stations. Site-specific empirical relationships between peak particle velocity, the amount of explosive and the distance were developed. These relationships were used to construct a practical blasting chart, which gives the maximum amount of explosive to be used as a function of distance, for future underground and surface blasting operations in the training field. Since the use of peak particle velocity in the field of civil engineering has been limited so far, site-specific parameters were also estimated to predict the blast-induced horizontal peak ground acceleration. Then, an attempt was made to investigate the dynamic responses of four and six storey reinforced concrete structures that consist of frame and shear wall type structural systems under the measured accelerations using finite element analysis. The limitations of this approach were discussed within the context of damage estimation.
  
  PubDate: 2013-04-17T11:00:48Z
Rotor platforms on pile-groups running through resonan A comparison between unbounded soil and soil-layers resting on a rigid bedrock
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Antonio Cazzani , Peter Ruge
  Rotor platforms supported by pile-groups typically run through resonance during start up and shut down. End-bearing pile-groups resting on a rather stiff underground surface cause additional layer-resonances compared with pile-groups driven into a half-space. On the other hand, the system's eigenfrequencies are accompanied by energy dissipation due to radiation damping. Thus the question arises, and is treated in this paper, if this radiation damping for end-bearing pile groups is strong enough to significantly suppress the additional resonance-peaks. The analysis uses dynamical stiffness coefficients in the frequency-domain for unbounded media recently published by Padrón et al. [1]. In order to treat transient excitations a transformation into the time-domain is necessary and is here realized through a rational representation which has been described and used in [2] but only for pile groups resting in an elastic half-space, which exhibit a much smoother behavior (with reference to frequency) than the case treated here.
  
  PubDate: 2013-04-17T11:00:48Z
Development of fragility functions for geotechnical constructions: Application to cantilever retaining walls
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Sotirios Argyroudis , Amir M. Kaynia , Kyriazis Pitilakis
  Fragility curves constitute an emerging tool for the seismic risk assessment of all constructions at risk. They describe the probability of a structure being damaged beyond a specific damage state for various levels of ground shaking. They are usually represented as two-parameter (median and log-standard deviation) cumulative lognormal distributions. In this paper a numerical approach is proposed for the construction of fragility curves for geotechnical constructions. The methodology is applied to cantilever bridge abutments on surface foundation often used in road and railway networks. The response of the abutment to increasing levels of seismic intensity is evaluated using a 2D nonlinear FE model, with an elasto-plastic criterion to simulate the soil behavior. A calibration procedure is followed in order to account for the dependency of both the stiffness and the damping on the soil strain level. The effect of soil conditions and ground motion characteristics on the global soil and structural response is taken into account considering different typical soil profiles and seismic input motions. The objective is to assess the vulnerability of the road network as regards the performance of the bridge abutments; therefore, the level of damage, is described in terms of the range of settlement that is observed on the backfill. The effect of backfill material to the overall response of the abutment wall is also examined. The fragility curves are estimated based on the evolution of damage with increasing earthquake intensity. The proposed approach allows the evaluation of new fragility curves considering the distinctive features of the structure geometry, the input motion and the soil properties as well as the associated uncertainties. The proposed fragility curves are verified based on observed damage during the 2007 Niigata-Chuetsu Oki earthquake.
  Highlights ► We propose a numerical approach for the construction of fragility curves for geotechnical constructions. ► We apply this approach to cantilever bridge abutments, using different geometries, seismic input motions and soil profiles. ► We examine the influence of the backfill material on the overall response of the abutment wall. ► Fragility curves for cantilever bridge abutments are evaluated and verified on the basis of observations from past earthquake. ► The role of soil is relevant and should be considered in the fragility analysis of geotechnical constructions.
  
  PubDate: 2013-04-13T12:31:22Z
In-plane shear behaviour of unreinforced and jacketed brick masonry walls
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Sergey Churilov , Elena Dumova-Jovanoska
  This paper deals with the results of cyclic load tests on masonry walls performed for the purpose of evaluation of in-plane shear behaviour and identification of shear strength, stiffness and energy dissipation. Eight walls in two series were assembled in laboratory conditions. The first series consisted of four unreinforced masonry walls constructed from solid clay bricks and lime mortar. The walls from the second series were strengthened by application of RC jackets on both sides. These were constructed of the same material and were characterized by the same geometry properties and vertical load levels as those of the walls from the first series. The main goal of the tests was to compare the behaviour of the unreinforced and strengthened walls under cyclic horizontal load. The results from the tests showed that the application of the strengthening method contributed to a significant improvement of the shear resistance of the jacketed walls. Analytical models were used to predict the shear resistance of the walls. Good agreement with the experimental results was obtained with a model based on tensile strength of masonry.
  
  PubDate: 2013-04-13T12:31:22Z
Slope topography effects on ground motion in the presence of deep soil layers
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): R. Tripe , S. Kontoe , T.K.C. Wong
  An extensive investigation has been made into the interaction between topographic amplification and soil layer amplification of seismic ground motion. This interaction is suggested in the literature as a possible cause for the differences between topographic amplification magnitudes observed in field studies and those obtained from numerical analysis. To investigate this issue a numerical finite element (FE) parametric study was performed for a slope in a homogeneous linear elastic soil layer over rigid bedrock subjected to vertically propagating in-plane shear waves (Sv waves). Analyses were carried out using two types of artificial time history as input excitation, one mimicking the build-up and decay of shaking in the time histories of real earthquake events, and the other to investigate the steady-state response. The study identified topographic effects as seen in previous numerical studies such as modification of the free-field horizontal motion, generation of parasitic vertical motion, zones of alternating amplification and de-amplification on the ground surface, and dependence of topographic amplification on the frequency of the input motion. For the considered cases, topographic amplification and soil layer amplification effects were found to interact, suggesting that in order to accurately predict topographic effects, the two effects should not be always handled separately.
  Highlights ► FE study for a slope in a soil layer overlying bedrock subjected to SV waves. ► Soil layer effects were found to be more significant than topographic effects. ► Soil layer and topographic amplifications occur at different normalised frequencies. ► Topographic and soil layer amplifications are not easily separated. ► Their interaction reduces with increasing bedrock depth.
  
  PubDate: 2013-04-13T12:31:22Z
Slope seismic stability analysis on kinematical element method and its application
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Ke Zhang , Ping Cao
  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.
  
  PubDate: 2013-04-13T12:31:22Z
Nonlinear dynamic foundation and frame structure response observed in geotechnical centrifuge experiments
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): N.W. Trombetta , H.B. Mason , Z. Chen , T.C. Hutchinson , J.D. Bray , B.L. Kutter
  Soil–foundation–structure interaction (SFSI) and structure–soil–structure interaction (SSSI) influence the seismic response of a structure. Yet, consideration of nonlinear SFSI and SSSI in design practice is lacking. In this paper data from two centrifuge tests are examined. During each test, inelastic models of (1) a low-rise frame with shallowly embedded footings and (2) a mid-rise frame with a large basement are subjected to earthquake motions. In the first test, the structures are separated. In the second test, the structures are placed next to each other. Results show that the presence of the deep basement affects the moment–rotation behavior of the adjacent shallow footings, stiffening the response in the direction of loading towards the basement. This can be attributed to the additional restraint provided by the basement. Although the presence of the basement stiffens the response, it also limits the permanent displacements of the footing, which in turn limits physical damage to the superstructure. These results suggest that in addition to considering nonlinear SFSI effects, SSSI should be considered in the design of closely clustered structures.
  Highlights ► We performed two seismic centrifuge tests at a scale of N=55. ► First, we recorded the baseline SFSI response of two inelastic structures. ► Second, we recorded the modified response of the structures when placed adjacent. ► Increased seismic demands are observed in the superstructure due to footing restraint. ► Footing moment–rotation response is modified for restrained footings.
  
  PubDate: 2013-04-13T12:31:22Z
The variational projection method (VPM): A modern technique to simulate the seismic response of shallow alluvial valleys
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): R. Ávila-Carrera , F.J. Sánchez-Sesma
  The variational projection method (VPM) to compute the seismic response of three-dimensional (3D) shallow al1uvial valleys is presented. The solution is based on a weak-form variational Galerkin formulation of the problem for a smooth irregular layer overlaying an elastic half-space. The Galerkin method is applied by means of a simple set of trial functions for depth dependence. The partial differential equations of dynamic elasticity in space and time are “projected” into the horizontal free surface plane and are then solved using a pseudospectral scheme: finite differences in time and fast Fourier transform (FFT) to compute spatial horizontal derivatives. By using as reference the 1D solution, the radiation conditions are approximately fulfilled. Numerical examples of the performance and accuracy of the method in 2- and 3D are given. Possible improvements of the method are discussed.
  Highlights ► We present a new methodology to compute seismic response of deposits. ► We develop a novel numerical formulation using a Galerkin scheme. ► Fast computations and acceptable approximations vs. other techniques. ► We propose a new and suitable set of absorbing boundary conditions.
  
  PubDate: 2013-04-13T12:31:22Z
A new limit equilibrium method for the pseudostatic design of embedded cantilevered retaining walls
- Abstract: Publication date: July 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  Author(s): Riccardo Conti , Giulia M.B. Viggiani
  This paper describes a new pseudostatic limit equilibrium method for the design of cantilevered retaining walls under seismic actions. The method has been applied in a parametric study of the effects of the geometry of the wall, considering different excavated and embedded depths, of the strength of the soil, and of the contact between the soil and the wall. The pseudostatic predictions are in very good agreement, both in terms of horizontal contact stress and bending moment distributions, with the results of truly dynamic 2-D finite difference analyses and published experimental data. It is found that for increasing strengths of the soil–wall system both the critical acceleration and the maximum bending moment on the wall increase. In other words, a stronger soil–wall system will experience smaller displacements during the earthquake, but this is paid for by increasing internal forces in the wall.
  
  PubDate: 2013-04-13T12:31:22Z
Editorial Board / Aims and Scope
- Abstract: Publication date: June 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  PubDate: 2013-04-13T12:31:22Z
Estimation of site effects in Delhi using standard spectral ratio
- Abstract: July 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  Delhi, a city of more than 10 million inhabitants, lies approximately 200km from Main Boundary Thrust (MBT) and 300km from Main Central Thrust (MCT), the two most active thrusts of the Himalayas. The city has a varying soil cover and some parts have thick sediments that can potentially amplify the earthquake shaking. Estimates of site effect in Delhi using the standard spectral ratio technique are available only at few locations and significantly differ from those computed from shear-wave profiles inferred from bore-hole penetration tests. Site effects have also been estimated in Delhi theoretically as well as using microtremor studies, yet their knowledge is significantly inadequate to assess true nature of ground amplification. In the present work, site amplification is estimated at 55 different sites in Delhi using data from 13 different earthquakes using the standard spectral ratio method. The site IMD Ridge (NDI) is taken as the reference site on the basis of local geology. The results show significant variations in amplification factor from one place to another. Higher amplification is observed at both banks of Yamuna river. There are some sites, where less or no amplification is observed. The predominant frequency is in general found to be lower near Yamuna banks than the other sites. Based on the observations, we also present an amplification map of the city.
  
  PubDate: 2013-04-05T17:00:31Z
Editorial Board / Aims and Scope
- Abstract: May 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 48
  
  PubDate: 2013-04-01T09:36:41Z
Directivity pulses in near-fault ground motions—II: Estimation of pulse parameters
- Abstract: July 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  The simulation of directivity pulse-type ground motions through superimposition of modelled directivity pulse(s) on a non-pulse type motion is a possible approach to meet the scarcity of such motions in studying the structural response under those. It is shown in the companion paper that the amplitude and dominant Fourier period of the expected velocity pulse for a given seismic scenario may be sufficient to model the shapes of the expected acceleration and velocity pulses. Scaling models are proposed in this paper for the estimation of these parameters and time of occurrence of the expected pulse in the case of primary pulse, together with relationships between the parameters of the primary and secondary pulses. The pulses extracted in the companion paper are considered for this purpose. A sensitivity analysis shows that uncertainties in the estimation of the primary pulse parameters significantly affect the pseudo-spectral acceleration (PSA), non-linear maximum displacement (SD) and hysteresis energy dissipation (EH) responses to the simulated motions, whereas uncertainties in the primary-secondary pulse relationships affect only the SD response significantly. It has been shown that for a pulse-type motion, an increase in earthquake magnitude may sometimes lead to a significantly lower response. Further, the presence of a directivity pulse leads to a significantly greater response at lower magnitudes, and at higher magnitudes for the periods near the pulse period and in the case of a nonlinear response.
  Highlights ► Simulation is considered by superposition of directivity pulse on non-pulse type motion. ► Scaling models are proposed for the amplitude and period of primary velocity pulse. ► Occurrence time of primary velocity pulse is proposed. ► Relationships between the primary and secondary pulse parameters are proposed. ► Effect of earthquake magnitude on structural response to directivity motions is studied.
  
  PubDate: 2013-04-01T09:36:41Z
Undrained deformation behavior of saturated soft clay under long-term cyclic loading
- Abstract: July 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  Subgrade soils of traffic infrastructures are subjected to large numbers of load applications at a stress level below their shear strength. It is therefore of great practical relevance to study the deformation behavior of soft clay under long-term cyclic loading. In this study, a series of monotonic triaxial tests and long-term cyclic (50,000 cycles) triaxial tests have been carried out to investigate the undrained deformation behavior of undisturbed soft clay from Wenzhou, China. The stress–strain hysteretic loop, resilient modulus and permanent strain of the tested samples were found significantly dependent on CSR and confining pressure. With an increase of CSR and confining pressure, the resilient modulus decreases more significantly with increasing number of cycles and the accumulation rate of permanent strain increases. Furthermore, the shape of the stress–strain hysteretic loop almost remains unchanged and the resilient modulus tends to a steady value after a large number of cycles. Based on the experimental results, two equations are established for the prediction of long-term resilient modulus and permanent strain. Finally, a new critical value of 0.65 is suggested for CSR. When CSR>0.65, the resilient modulus for large number of cycles is reduced to a so called “asymptotic stiffness” and the accumulation rate of permanent strain significantly increases.
  Highlights ► A series of long-term cyclic (50,000 cycles) triaxial tests are carried out. ► Deformation behavior is significantly dependent on CSR and confining pressure. ► After large number of cycles, the resilient modulus tends to be a steady value. ► Two equations are given for long-term resilient modulus and permanent strain. ► A new critical value of 0.65 is suggested for CSR.
  
  PubDate: 2013-04-01T09:36:41Z
Directivity pulses in near-fault ground motions—I: Identification, extraction and modeling
- Abstract: July 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  In ensuring structural safety against near-fault pulse-type ground motions it is of critical importance that sufficient recorded motions of this type are available and that suitable synthetic motions can be simulated for those situations where the recorded motions are insufficient or non-existent. To this end, an objective criterion is developed for the directivity pulse-type motions, to identify such motions from the available suite of recorded ground motions. This criterion is based on the value of maximum fractional signal energy contribution by any half-cycle of the velocity time-history. For the simulation of directivity pulse-type motions, it is proposed to estimate and superimpose directivity pulse(s) on a non-pulse type motion. An algorithm is developed to extract the directivity pulse features from a pulse-type accelerogram via its repetitive smoothening, and based on the pulses extracted from a database of 91 records two mathematical functions are proposed to model the directivity pulses. It is found that the amplitude and dominant Fourier period of the expected velocity pulse may be sufficient to generate the shapes of the expected acceleration and velocity pulses.
  Highlights ► An energy-based pulse identifier for identifying directivity-pulse type motions is proposed. ► An algorithm for extracting directivity pulses from pulse-type ground motions is proposed. ► Two types of directivity pulses are identified from 91 pulse-type motions. ► Analytical models based on the Mexican Hat function are proposed for the two pulse types. ► Amplitude and dominant Fourier period of velocity pulse are inputs for the proposed models.
  
  PubDate: 2013-03-28T12:00:05Z
Damage evaluation of concrete gravity dams under mainshock–aftershock seismic sequences
- Abstract: July 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 50
  
  A large mainshock may trigger numerous aftershocks within a short period, and large aftershocks have the potential to cause additional cumulative damage to structures. This paper investigates the effects and potential of aftershocks on the accumulated damage of concrete gravity dams. For that purpose, 30 as-recorded mainshock–aftershock seismic sequences are considered in this study, and a typical two-dimensional gravity dam model subjected to the selected as-recorded seismic sequences is modeled. A Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is selected for the concrete material. This model is used to evaluate the nonlinear dynamic response and the seismic damage process of Koyna dam under mainshock–aftershock seismic sequences. According to the characteristics of the cracking damage development, the local and global damage indices are both established to study the influence of strong aftershocks on the cumulative damage of concrete gravity dams. From the results of this investigation, it is found that the as-recorded sequences of ground motions have a significant effect on the accumulated damage and on the design of concrete gravity dams.
  Highlights ► 30 mainshock–aftershock seismic sequences are used as seismic excitations. ► A Concrete Damaged Plasticity model is used in seismic damage analysis. ► Local and global damage indices for damage evaluation are proposed. ► The effects of aftershcok on the accumulated damage of gravity dams are discussed. ► The damage to the upper zone of the dam is more sensitive to the aftershock.
  
  PubDate: 2013-03-28T12:00:05Z
A generalized log-spiral-Rankine limit equilibrium model for seismic earth pressure analysis
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  A method of slices for estimating seismic earth pressures due to earthquake-induced pseudo-static body forces is presented herein. The method is based on a limit-equilibrium approach, and utilizes a composite logarithmic spiral failure surface along which the Mohr-Coulomb failure criterion is enforced. The model explicitly accounts for the magnitude of earthquake acceleration, the structure's height, the backfill soil properties (e.g., internal friction angle, and cohesion), and the mobilized interface friction angle between the backfill and the earth-retaining structure. Majority of the previous analytical (or semi-analytical) methods neglect the effects of soil's cohesion and/or use simple planar failure surfaces. Parametric studies conducted with the proposed method, as well as a number of prominent others indicate that the aforementioned simplifying assumptions often yield significantly different estimates of seismic earth pressures from the more general model proposed here, and that they may lead to sub-optimal or unsafe designs.
  Highlights ► An analytical model for assessing seismic earth pressures is proposed. ► The effects of inter-particle friction and cohesion of backfill soil are considered. ► The model's predictions are verified against 6 prominent existing analytical models. ► Soil cohesion drastically decreases the resultant active earth-pressure force. ► Soil cohesion considerably increases the resultant passive earth-pressure force.
  
  PubDate: 2013-03-28T12:00:05Z
Rapid on-site peak ground acceleration estimation based on support vector regression and P-wave features in Taiwan
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  This study extracted some P-wave features from the first few seconds of vertical ground acceleration of a single station. These features include the predominant period, peak acceleration amplitude, peak velocity amplitude, peak displacement amplitude, cumulative absolute velocity and integral of the squared velocity. The support vector regression was employed to establish a regression model which can predict the peak ground acceleration according to these features. Some representative earthquake records of the Taiwan Strong Motion Instrumentation Program from 1992 to 2006 were used to train and validate the support vector regression model. Then the constructed model was tested using the whole earthquake records of the same period as well as the 2010 Kaohsiung earthquake with 6.4 M L . The effects on the performance of the regression models using different P-wave features and different length of time window to extract these features are studied. The results illustrated that, if the first 3s of the vertical ground acceleration was used, the standard deviation of the predicted peak ground acceleration error of the whole tested 15-years earthquake records is 20.89gal.The length of time window could be shortened, e.g. 1s, and the prediction error is slightly sacrificed, in order to prolong the lead-time before destructive S-waves reaches.
  Highlights ► PGA was estimated by support vector regression models. ► The necessary information is the P-wave features of vertical record on a single station. ► The proposed approach was validated by 15-years earthquake records of TSMIP in Taiwan. ► Another earthquake event was tested to illustrate the feasibility and possible acquired lead-time.
  
  PubDate: 2013-03-28T12:00:05Z
The reflection of P-waves in a poroelastic half-space saturated with viscous fluid
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  This paper presents the surface strains, rocking strains, and energy partitions in a poroelastic half-space saturated with viscous fluid during the reflection of P-waves. In this paper, the effect of seepage force due to finite skeleton permeability and viscosity of the fluid are presented, mainly to show the effect of permeability on the surface strains, rocking, and energy partitions during the reflection of fast P-waves. Biot's theory of wave propagation in fluid-saturated porous media is used to describe the motion of the medium of the half-space. Numerical results are presented in terms of the angle of incident P-waves and Poisson's ratio for various properties and degrees of solid frame stiffness. It is found that the skeleton permeability affects the strains, rocking, and energy partitions in porous, stiff media, while its effect is negligible in the case of soft soil.
  Highlights ► The paper studies the surface strains, rocking strains, and energy partitions. ► The effects of seepage force are considered. ► The effect of permeability is studied.
  
  PubDate: 2013-03-28T12:00:05Z
Strain effects on kinematic pile bending in layered soil
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  The kinematic bending of single piles in two-layer soil is explored to account for soil stiffness degradation and associated damping increase with increasing levels of shear strain, a fundamental aspect of soil behaviour which is not incorporated in current simplified seismic design methodologies for pile foundations. A parametric study of a vertical cylindrical pile embedded in a two-layer soil profile to vertically-propagating S waves, carried out in the time domain by a pertinent beam-on-dynamic-Winkler-foundation (BDWF) model, is reported. Strain effects are treated by means of the equivalent-linear procedure which provides soil stiffness and damping ratio as function of shear strain level. Whereas the approach still represents a crude representation of the actual soil behaviour to dynamic loading, it is more realistic than elementary solutions based on linear visco-elasticity adopted in earlier studies. The paper highlights that soil nonlinearity may have either a detrimental or a beneficial effect on kinematic pile bending depending on the circumstances. The predictive equations for kinematic pile bending in visco-elastic soil recently developed by the
  Authors are extended to encompass strain effects. Numerical examples and comparisons against experimental data from case histories and shaking table tests are presented.
  Highlights ► Kinematic pile bending is explored accounting for soil strain dependence. ► Strain effects are treated by means of the equivalent-linear procedure. ► Numerical examples and comparisons against experimental data are presented. ► Soil nonlinearity may be detrimental or beneficial for kinematic pile bending. ► Previous predictive equations are extended to encompass soil strain effects.
  
  PubDate: 2013-03-28T12:00:05Z
Optimum design of Tuned Mass Dampers by displacement and energy perspectives
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Tuned Mass Dampers are extensively used for vibration control in many engineering fields, such as civil, mechanical and aeronautical. The present work focuses on the analysis of the effectiveness of this passive vibration control strategy. Its goal is to test the Tuned Mass Damper performance both from the energy and from displacement perspectives. For this purpose, a simple single degree of freedom system subject to a dynamic action and equipped with a Tuned Mass Damper is analyzed. The device performance is estimated by two indicators that are related to the reduction of the maximum displacement and dissipated energy into the primary system. These indices will be adopted as objective functions to perform an optimization procedure based on two different criteria, to obtain Tuned Mass Damper parameters, which give the best performances. Different circumstances, which reflect on various characterizations of the input and of the main system, are analyzed.
  Highlights ► Tuned Mass Damper optimization performance both from the energy and displacement prospective. ► Simple single degree of freedom system subject to a dynamic action and equipped with a Tuned Mass Damper is analyzed. ► Two indicators related to maximum displacement and dissipated energy reduction into the primary system.
  
  PubDate: 2013-03-28T12:00:05Z
Excess pore pressure dissipation and solidification after liquefaction of saturated sand deposits
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  To understand the post-liquefaction behavior of liquefied ground, it is important to get a better understanding and a more suitable characterization of the variation of excess pore pressure after liquefaction. In this paper, the soil permeability is considered as one of the key soil parameters for clarifying the mechanism of post-liquefaction behavior of liquefied ground. For this reason, a series of shaking table tests were conducted for a Toyoura sand deposit with different soil permeability values. Polymer fluid was used in model tests to vary the permeability of sand deposits. Excess pore pressures and settlements were measured in each test. A basic mechanism in post-liquefaction behavior and the solidification phenomenon after liquefaction were discussed based on these test results. Also, a new method for predicting the dissipation of excess pore pressure was developed. This study provides evidence of the important effect of soil permeability on the velocity with which the solidification front moves upward in liquefied ground. It is suggested that the value of coefficient of permeability of liquefied sand can increase to about 4.0 times the initial value. This variation of permeability after liquefaction should be taken into account in post-liquefaction analysis.
  Highlights ► An equation was suggested to simulate the solidification velocity in liquefied sand. ► A new method was developed to predict the dissipation of excess pore pressure. ► Sand permeability can increase up to 4.0 times during the dissipation process. ► The settlement can be properly simulated based on the predicted dissipation curves.
  
  PubDate: 2013-03-24T12:00:05Z
Dynamic soil–structure interaction of monopile supported wind turbines in cohesive soil
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Offshore wind turbines supported on monopile foundations are dynamically sensitive because the overall natural frequencies of these structures are close to the different forcing frequencies imposed upon them. The structures are designed for an intended life of 25 to 30 years, but little is known about their long term behaviour. To study their long term behaviour, a series of laboratory tests were conducted in which a scaled model wind turbine supported on a monopile in kaolin clay was subjected to between 32,000 and 172,000 cycles of horizontal loading and the changes in natural frequency and damping of the model were monitored. The experimental results are presented using a non-dimensional framework based on an interpretation of the governing mechanics. The change in natural frequency was found to be strongly dependent on the shear strain level in the soil next to the pile. Practical guidance for choosing the diameter of monopile is suggested based on element test results using the concept of volumetric threshold shear strain.
  Highlights ► Dynamic SSI of offshore wind turbines are explored through small scale tests. ► Scaling laws/similitude relationships are derived. ► Guidance for choosing monopile diameter suggested based on element test results. ► Micro behaviour (element tests) linked to macro behaviour (model tests).
  
  PubDate: 2013-03-24T12:00:05Z
A non-parametric wave type based model for real-time prediction of strong ground motion accelerogram
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  A wave type based method for real-time prediction of strong ground motion (SGM) accelerogram is developed. Real-time prediction of SGM is requested in predictive building control systems to trigger and control actuator systems achieving the goal of reduction of the structural deformations during an on-going earthquake. It is well known that SGM is a classic example of non-stationary stochastic process with temporal variation of both amplitude and frequency content. The developed non-parametric model considers the non-homogeneity of the seismic process which contains different wave types with the individual frequency contents and time-dependency amplitude distribution pattern. Therefore, an important part of the method is to detect dominant seismic wave phases. Prediction of seismic signal is undertaken by applying frequency adaptive windowing approach, which leads to predict the on-coming signal in time window t+Δt based on the measured data in the time window t. Besides use of the frequency adaptive windowing, constant windowing and semi-adaptive windowing approaches are deployed. The results show that use of the adaptive time windows relevant to dominant frequency of the signal will enable the model to catch and predict the most dominant frequencies. Performance of the proposed model is verified by the use of 97 free-field accelerograms, which were applied to train and validate the prediction model. The selected accelerograms were measured above the soil type C and D according Eurocode 8 and their Moment magnitude are ranging between 6.2 and 7.7. The learning capability of the radial basis function Artificial Neural Network is used to reconstruct the SGM accelerogram. The most significant advantage of the proposed model is the concept of wave type based modeling which has the advantage of a conceptual physical modeling of the seismic process. Comparison of the real-time predicted and the observed accelerograms shows a high correlation when the frequency adaptive approach is applied. This paper lays a foundation for more effective use of real-time predictive control systems and potential for future extension in active structural control as well as in real-time seismology.
  Highlights ► A wave type based method for real-time prediction of ground motion is developed. ► Real-time prediction of SGM is requested in predictive building control systems. ► Prediction of the SGM is undertaken by using a frequency adaptive approach. ► The results show that the model is able to catch the most dominant frequencies.
  
  PubDate: 2013-03-24T12:00:05Z
Experimental investigation of plastic demands in piles embedded in multi-layered liquefiable soils
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Multi-layered soil profiles, where one or more layers consist of loose liquefiable material, most commonly require pile foundations extending beyond the liquefiable layer to competent material. Under seismic loads, if the loose layer liquefies, then large localized plastic demands may be generated in the piles. To study this behavior and provide detailed data to validate numerical models, a 1-g shaking table experiment was conducted considering a single reinforced concrete pile embedded in a three-layer soil system. The model pile of 25cm diameter was tested under increasing amplitude earthquake excitation in a sloped laminar soil box. The test specimen was designed at the lower bound of typical design to promote yielding, per ATC-32 (Applied Technology Council, 1996) [1]. The pile penetrated 7D (D=pile diameter) into a multi-layered soil configuration composed of a stiff uppermost crust overlying a saturated loose sand layer and a lower dense layer of sand. Plastic demands in the pile were characterized using curvature profiles coupled with back-calculation of the plastic hinge length and post-test physical observations. Results from this test quantify the post-yield behavior of the pile and serve as a complement to previously conducted centrifuge tests.
  Highlights ► The pile's region of plastic behavior was near the interface of the crust and loose sand layer. ► Location of plastic region of pile was consistent with field and prior tests observations. ► The pile's plastic region was spread over 1.5D length. ► Soil layer movements suggest that the pile may restrain the crust but not the loose sand layer.
  
  PubDate: 2013-03-20T12:00:07Z
Numerical simulation of mitigation of liquefaction seismic risk by preloading and its effects on the performance of structures
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  The present paper deals with the influence of soil non-linearity, introduced by soil liquefaction, on the soil-foundation–structure interaction phenomena. Numerical simulations are carried out so as to study an improvement method to reduce the liquefaction potential in a sandy soil profile subjected to a shaking. The efficiency of the preloading in both the mitigation of a liquefiable soil and the reduction of induced structure relative settlements is showed. However, the intervention at the foundation soil modifies the dynamic characteristics of soil–structure system and it seems to increase the induced seismic forces during earthquake. In addition, a numerical parametric analysis is performed so as to quantify the impact of the uncertainties associated with the input signal on both the ground motion and the apparition of liquefaction phenomena.
  Highlights ► The foundation soil mitigation modifies the characteristics of soil–structure system. ► Preloading produces significant reduction of structural settlement. ► Preloading could increase the structural seismic demand. ► Mitigation method decreases the liquefaction probability for a given seismic hazard.
  
  PubDate: 2013-03-16T12:00:20Z
An efficient approach for dynamic impedance of surface footing on layered half-space
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  A semi-analytical model for the evaluation of dynamic impedance of rigid surface footing bonded to multi-layered subsoil is proposed. The technique is based on the dual vector form of wave motion equation and Green's influence function of subdisk for horizontally layered half-space. The multi-layered half-space is divided into a quite large number of mini-layers and the precise integration method (PIM) is introduced for the numerical implementation. The PIM is highly accurate for solving sets of first-order ordinary differential equations with specified two-end boundary conditions. It can produce numerical results of Green's influence functions up to the precision of computer used. The dual vector form of wave motion equation makes the combination of two adjacent mini-layers/layers very easy. As a result, the computational effort for the evaluation of Green's influence function of the multi-layered half-space is reduced to a great extent. In order to satisfy the mixed boundary condition at the surface, the footing–soil interface is discretized into a number of uniformly spaced subdisk-elements. Comparisons illustrating the efficiency and accuracy of the proposed approach are made with a number of solutions available in the literature.
  Graphical abstract Highlights ► A new approach for the dynamic response analysis of 3-D footing–soil interaction. ► The soil can be half-space or multilayer soil. ► PIM can solve problem with less calculated effort, while achieving higher accuracy. ► PIM can avoid the index overflow problems of transfer matrices method. ► No limitation is imposed on the thickness of the layer for the new approach.
  
  PubDate: 2013-03-16T12:00:20Z
Scattering of plane P, SV or Rayleigh waves by a shallow lined tunnel in an elastic half space
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Based on the plane complex variable theory and the image technique, an analytical solution is presented for scattering of plane harmonic P, SV or Rayleigh waves by a shallow lined circular tunnel in an elastic half space. The major contribution of this study is the treatment of the orthogonality of the boundary conditions along the half surface and the cavity wall. In terms of the image technique, the scattered waves by the half surface are simulated as transmitting from the image source of the origin of the tunnel. Using two different conformal mapping functions, we obtained the complex-valued stresses and displacements of the elastic medium and the liner in the image domain, respectively. The boundary value problem results in a set of infinite algebraic equations. The accuracy of the present approach is verified by comparing the present solution results with the available published data. Parametric study indicates that the embedment depth, the shear modulus and the thickness of the liner have significant influences on the dynamic response of the liner and the medium.
  Highlights ► Scattering of plane waves by a lined tunnel in a half space are derived analytically. ► Scattered waves by the half surface is determined by the image technique. ► Increasing the depth of the tunnel cannot reduce its stress concentrations. ► Increasing the tunnel's rigidity results in greater stress concentration of the liner. ► Increasing the tunnel's thickness leads to greater stress concentration of the liner.
  
  PubDate: 2013-03-16T12:00:20Z
Earthquake damage analysis of arch dams considering dam–water–foundation interaction
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  A comprehensive model is integrated in this paper to analyze the nonlinear earthquake response of arch dams. The following factors are taken into account: the semi-unbounded size of foundation rock and compressible water, the opening of contraction joints, the cracking of the dam body, and the spatial variation of ground motions. As a case study, the earthquake response of the Pacoima dam to the 1994 Northridge earthquake is investigated using the proposed model. The earthquake damage is simulated based on the actual conditions during the earthquake to verify the developed analysis model. The joint opening and concrete cracking are qualitatively reproduced, wherein the ground motion excitation is spatially defined based on the acceleration records at the dam–rock interface. Several influencing factors, such as the earthquake input mechanism, shape of the thrust block, and water level, are further considered to analyze their contribution to the actual damage. The result shows that the variation of ground motions along the dam–foundation interface may be the most important factor for the damage mode of the Pacoima dam.
  Graphical abstract Highlights The computed damage distribution on the downstream face of the Pacoima dam due to the 1994 Northridge earthquake. ► We integrated a comprehensive model for earthquake damage analysis of arch dams. ► The model considers all important factors affecting earthquake response of arch dams. ► The actual damage of the Pacoima dam during the 1994 earthquake was reproduced. ► The earthquake input model has a significant effect on the damage mode of arch dams. ► The full reservoir may worsen the damage of the Pacoima dam during the 1994 earthquake.
  
  PubDate: 2013-03-16T12:00:20Z
Prediction of excess pore water pressure and post-cyclic settlement on soft clay induced by uni-directional and multi-directional cyclic shears as a function of strain path parameters
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  The effects of cyclic shear direction, shear strain amplitude and number of cycles on the accumulation of excess pore water pressure and on the recompression were investigated for a cohesive soil by using the multi-directional cyclic simple shear test apparatus in which the uniform or irregular cyclic shear strain was applied to the specimen from two perpendicular directions in the horizontal plane. It is shown that at the same shear strain amplitude and number of cycles, excess pore water pressure and post-cyclic settlement induced by multi-directional cyclic shear are larger than those generated by uni-directional one. For multi-directional cases, these parameters increase with the phase difference. The unique relations of the excess pore water pressure ratio and the post-cyclic settlement versus cumulative shear strain are obtained for uni-directional and multi-directional cyclic shears and also for multi-directional cyclic shear with various phase differences, and these results lead the effect of cyclic shear direction to be negligible. Furthermore, an estimation method of excess pore water pressure ratio and post-cyclic settlement is presented and the validity of this method is confirmed for both uniform and irregular cyclic shears.
  Highlights ► Cyclic shear direction affects cyclic induced-pore water pressure and settlement. ► Effects of cyclic shear direction can be eliminated by using cumulative shear strain. ► Pore water pressure induced by uniform and irregular cyclic shears can be simulated. ► Post-earthquake settlement can be estimated.
  
  PubDate: 2013-03-16T12:00:20Z
Tracking the dynamic characteristics of a nonlinear soil-pile system in multi-layered liquefiable soils
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Saturated soils, particularly cohesionless soils, may liquefy when subjected to earthquake excitation, resulting in reductions in strength and stiffness of the soil. A change in stiffness equates to a change in period, and hence, in response to future seismic loading. Furthermore, for pile foundations, a reduction of vertical or lateral soil resistance may cause failure of the structure. To study this, a unique one-g soil-pile model was constructed in a gently sloped laminar soil box which was subsequently placed on a uniaxial shake table. A 3-layer soil configuration of a stiff crust, liquefiable sand, and dense sand layer was constructed with an embedded pile and subjected to sequentially increasing amplitude earthquake motions. Lateral spreading of the liquefiable sand layer and stiffness degradation of the crust during shaking events were observed. The percent change in period may be translated to a change in effective shear modulus to articulate the softening effect of the system. To investigate this degradation, spectral and fourier ratios are computed and analyzed to study the nonlinear dynamic state of the pile-multi-layered soil system.
  Highlights ► Small amplitude input motions to the soil-pile system have a softening effect on the soil layers. ► Degradation in soil-pile stiffness is reflected by its changes in period for sequential motions. ► Knowledge of the state of a soil-pile system increases the reliability of numerical prediction.
  
  PubDate: 2013-03-16T12:00:20Z
A precise integration approach for dynamic impedance of rigid strip footing on arbitrary anisotropic layered half-space
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  The precise integration method (PIM) is proposed for the dynamic response analysis of rigid strip footing resting on arbitrary anisotropic multi-layered half-space. In the frequency domain, the governing equation of wave motion is converted into dual vector form of first-order ordinary differential equations which is solved by PIM. Each layer is divided into a large number (say, 2N) of mini-layers of equal thickness, within which characteristic matrices are assumed to vary following the Taylor series expansion to the fourth order. As a result, any desired accuracy of the displacements and stresses can be achieved by PIM. In addition, dual vector form equation makes it quite easily to combine two adjacent mini-layers into a new one. Each pass of combination reduces the total number of mini-layers by a half. The computational effort for the evaluation of the dynamic impedance of rigid strip footing can be reduced to a great extent. Numerical examples are provided to validate the efficiency and accuracy of the proposed approach.
  Highlights ► A new approach for the dynamic response analysis of soil-footing interaction. ► The soil can be any anisotropic multi-layered half-space. ► PIM can solve problem with less calculated effort and high accuracy. ► PIM can avoid the index overflow problems of transfer matrices method. ► No limitation is imposed on the thickness of the layer for the new approach.
  
  PubDate: 2013-03-16T12:00:20Z
Numerical simulation on seismic liquefaction by adaptive mesh refinement due to two recovered fields in error estimation
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  The finite element method is widely employed in numerical analysis of seismic liquefaction at present. However, due to the mesh distortion in strong dynamic action, the results are generally inaccurate and can even stop the calculation. Therefore, an adaptive mesh refinement (AMR) scheme is introduced to improve the numerical results based on a finite element and finite difference coupled dynamic method (FEM–FDM). The changing law about the errors due to the linear and the bilinear recovered fields of coarse meshes, AMR meshes and fine meshes is discussed. The seismic response on soil is compared between different AMR meshes. The AMR strategy can better simulate seismic liquefaction and offer more accurate results than the normal finite element simulation.
  Highlights ► An adaptive mesh strategy is employed in the analysis of liquefaction and flow. ► Two recovered field are used for the SPR error estimation, respectively. ► The bilinear and the linear fields can result in the same adaptive mesh. ► The bilinear field is suitable for the multi-mesh of 3- and 4- elements. ► This AMR can give a respective accurate result of the simulation.
  
  PubDate: 2013-03-16T12:00:20Z
Relationship between limiting shear strain and reduction of shear moduli due to liquefaction in large strain torsional shear tests
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  With the spread of performance-based design concepts in geotechnical earthquake engineering, conducting a practical and accurate analysis for estimating the liquefaction-induced ground deformation has become important. However, there is a difficulty in setting relevant parameters of liquefied soil that would be employed in the analysis because experimental investigations on large deformation behaviour of liquefied soil are still limited. Therefore, in order to investigate the liquefaction-induced ground deformation characteristics, a series of undrained cyclic torsional shear tests was performed by using a modified torsional shear apparatus that is capable of achieving double amplitude shear strain up to about 100%. The tested materials were saturated Toyoura sand, two kinds of in-situ frozen samples having different geological ages and their reconstituted samples. The in-situ samples were retrieved from Pleistocene deposits. In all the undrained cyclic torsional shear tests, cyclic mobility was observed and the double amplitude shear strain approached 100%, irrespective of the different initial conditions of the specimens. A limiting value of double amplitude shear strain to cause strain localization, which would be linked to the maximum possible liquefaction-induced ground deformation, was evaluated based on the change in the deviator stress during the undrained cyclic torsional loading. The limiting value was found to increase with decrease in initial values of small strain shear moduli which were evaluated by dynamic measurement. In addition, we measured tangent shear moduli at the limiting state as well as after strain localization, and evaluated a reduction ratio of shear moduli due to liquefaction, which would be employed in the ALID framework. These characteristics measured by such large strain liquefaction tests would be useful in estimating the maximum liquefaction-induced ground deformation.
  Highlights ► Large strain liquefaction tests were performed by modified torsional shear apparatus. ► Tested materials were Toyoura sand and two kinds of in-situ frozen samples. ► Limiting strain to cause strain localization was evaluated. ► We evaluated a reduction of shear moduli by liquefaction employed in ALID framework.
  
  PubDate: 2013-03-16T12:00:20Z
Direct differentiation method for response sensitivity analysis of a bounding surface plasticity soil model
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Finite element (FE) response sensitivity analysis is an important component in gradient-based structural optimization, reliability analysis, system identification, and FE model updating. In this paper, the FE response sensitivity analysis methodology based on the direct differentiation method (DDM) is applied to a bounding surface plasticity material model that has been widely used to simulate nonlinear soil behavior under static and dynamic loading conditions. The DDM-based algorithm is derived and implemented in the general-purpose nonlinear finite element analysis program OpenSees. The algorithm is validated through simulation of the nonlinear cyclic response of a soil element and a liquefiable soil site at Port Island, Japan, under earthquake loading. The response sensitivity results are compared and validated with those obtained from Forward Finite Difference (FFD) analysis. Furthermore, the results are used to determine the relative importance of various soil constitutive parameters to the dynamic response of the system. The DDM-based algorithm is demonstrated to be accurate and efficient in computing the FE response sensitivities, and has great potential in the sensitivity analysis of nonlinear dynamic soil-structure systems.
  Highlights ► A finite element response sensitivity algorithm for a bounding surface soil model. ► Response sensitivity analysis of a liquefiable soil ground under earthquake loading. ► Great potential in sensitivity analysis of nonlinear dynamic soil-structure systems.
  
  PubDate: 2013-03-16T12:00:20Z
Physical modelling of shaking table tests on dynamic soil–foundation interaction and numerical and analytical simulation
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  Earthquake geotechnical engineering has been recognised as an important branch of earthquake engineering. The analysis of soil–structure interaction may also be crucial when structural design problems are involved. Soil–structure interaction is a complex problem and needs to be analysed by physical and numerical modelling. Two physical models, consisting of a shallow foundation resting on a sand deposit, are tested on a shaking table to analyse soil–foundation interaction. The physical models are monitored, recording the time-histories of accelerations and displacements in the soil deposit and on the foundation. FEM codes are then employed to numerically model the resulting behaviour, using specific constitutive models and a new hand-made code based on the characteristic-line method. Simplified analytical approaches, still preferred in engineering, are discussed and developed. A comparison is made between the numerical and analytical results and they are also compared with the experimental results to validate the numerical modelling and analytical approaches and, in the new light of the Performance-Based-Design, evaluate their ability to predict foundation displacements (SLE) and bearing capacity (SLU). Finally, interesting aspects regarding the seismic behaviour of the shallow foundation on the sand deposit have been observed and noted.
  Highlights ► Physical and numerical modelling and analysis of the entire soil–foundation system. ► Soil D r control: a key-point for shaking table tests on DSFI. ► Settlements by soil sliding failure for massive foundations are the most important. ► Soil inertia for SLU evaluation is well estimated with a new method. ► Experimental, numerical and analytical results leads to γ Rd less than 1.
  
  PubDate: 2013-03-08T12:00:08Z
Comparison of ground models estimated from surface wave inversion using synthetic microtremors
- Abstract: June 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 49
  
  A parametric study on synthetic microtremors is proposed to compare the suitability of two ground models estimated from two surface wave inversions. Synthetic microtremors for array stations are calculated by controlling the magnitude of input sources applied on the ground surface, through the parameter “ratio of forces” R F. The value for R F is determined by the minimum misfit between synthetic vertical/horizontal component dispersion curves and, by quantitative comparison of the value of synthetic H/V spectral ratio predominant frequency and its spectral amplitude, with the experimental ones obtained at a Swiss site.
  Highlights ► Comparison of ground models is proposed using synthetic microtremors. ► The ratio of forces R F is used to fit synthetic dispersion curve to experimental one. ► Rayleigh dispersion inversion is enhanced by the H/V predominant frequency.
  
  PubDate: 2013-03-08T12:00:08Z
Incremental dynamic analysis of wood-frame houses in Canada: Effects of dominant earthquake scenarios on seismic fragility
- Abstract: May 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 48
  
  Seismic fragility can be assessed by conducting incremental dynamic analysis (IDA). This study extends the current conditional mean spectrum (CMS)-based record selection approach for IDA by taking into account detailed seismic hazard information. The proposed method is applied to conventional wood-frame houses in Canada, across which dominant earthquake scenarios and associated hazard levels vary significantly. Effects due to different seismic environments, site conditions, CMS-based record selection methods, and house models are investigated by comparing various seismic fragility models. Moreover, relative impact of the key characteristics is evaluated in terms of seismic loss curve for a group of wood-frame houses. Importantly, a close examination of regional seismic hazard characteristics using seismic hazard curve and seismic deaggregation facilitates the deeper understanding of the impact of ground motion characteristics on seismic fragility. A comprehensive and systematic assessment of key uncertainties associated with seismic fragility is provided.
  Highlights ► Incremental dynamic analysis is conducted for conventional wood-frame houses in Canada. ► Detailed seismic hazard information is incorporated in selecting input ground motion records. ► Multiple conditional mean spectra for different earthquake scenarios are developed. ► Impact of regional seismicity, site condition, record selection methods, and structural capacity is assessed in detail. ► The effects of different seismic fragility assessments on seismic loss estimation are evaluated.
  
  PubDate: 2013-03-04T12:00:24Z
Dynamic analyses of multilayered poroelastic media using the generalized transfer matrix method
- Abstract: May 2013
  Publication year: 2013
  Source:Soil Dynamics and Earthquake Engineering, Volume 48
  
  Since the generalized transfer matrix method overcomes the intrinsic instability of the Thomson–Haskell transfer matrix method for both high frequencies and/or thick layers, it can produce stable and accurate solutions for the dynamic analysis of viscoelastic media as well as anisotropic media. This paper extends the generalized transfer matrix method to the dynamic analysis of multilayered poroelastic media. Main improvements include the presentation of the concisely explicit general solutions for the dynamic analysis of multilayered poroelastic media and the derivation of an analytical inversion of 8×8 order layer matrix corresponding to the general solutions. The explicit solutions are valid for the dynamic analysis of one-dimensional, two-dimensional and three-dimensional poroelastic medium problems. In addition, an efficient recursive scheme is proposed for accurate determination of the equivalent interface sources for multilayered poroelastic media due to excitation by a source at an arbitrary depth. For the dynamic analysis of multilayered poroelastic media, the generalized transfer matrix method recursively transfers both the interface stiffness matrix and equivalent source starting from the bottom half space to the top layer, without resort to the numerical solution of the assembled global equations as the exact stiffness matrix method does. While keeping the simplicity of the Thomson–Haskell transfer matrix method, the generalized transfer matrix method is both accurate and stable. The related numerical examples have demonstrated that the generalized transfer matrix method is an alternative approach to conducting the dynamic analysis of multilayered poroelastic media.
  Highlights ► Stable transfer matrix method for dynamic analyses of layered poroelastic media. ► Presentation of an explicit general solutions for one-dimensional, two-dimensional and three-dimensional poroelastic media. ► Derivation of an analytical inversion of 8×8 order layer matrix. ► Accurate determination of the stiffness matrix and equivalent interface sources.
  
  PubDate: 2013-02-28T09:09:23Z