Seismic Response Of Soil Research Articles

Seismic site effects in Lisbon: the role of complex geological and morphological conditions

Lisbon’s historical seismicity, socioeconomic importance and population density contribute to a moderate to high seismic risk. The geological setting of the city includes cases of inclined layers, interbedding sedimentary rock layers in soil deposits, sand and clay layers in the same geological unit, leading to cases of shear wave velocity inversion and a large scatter of geotechnical properties within each geological unit. The morphological setting of the city is characterised by the existence of several hills and relatively shallow, stream-carved valleys filled with alluvial deposits. The seismic site effects in Lisbon were assessed through numerical simulation using the linear equivalent method and adopting the two types of seismic action defined in the Portuguese National Annex of Eurocode 8: (i) one-dimensional subsoil models covering the city, at sites where borehole data and geophysical data were available; (ii) two-dimensional subsoil models along three cross-sections representative of the geological settings and morphology. The distribution of amplification factors in the city revealed a pattern related to ground characteristics that impact seismic soil response, such as the presence of high-thickness cover deposits, significant shear-wave variations, alluvial valleys, a crest or significant slope variations and inclined layers. The 2D/1D spectral ratio highlighted the areas were 2D seismic effects are more important. The soil factor determined in the numerical analyses was consistently greater than the soil factor values indicated in Eurocode 8.

Predicting the seismic ground-motion parameters: 3D physics-based numerical simulations combined with artificial neural networks

Typically, it is challenging to incorporate near-surface soils into 3D physics-based numerical simulations (PBSs) for ground-motion prediction. The low shear wave speed of near-surface soils, coupled with the complexity of the soil seismic response, poses significant difficulties. To overcome these limitations, a hybrid approach was proposed in this study, combining PBSs with artificial neural networks (ANNs). The essence of the hybrid method can be summarized as follows: (1) development of ANN models, establishing a strong-motion database, training the ANNs on it to predict the ground-motion parameters for East–West (EW), North–South (NS), and Vertical (UD) directions afterward; (2) establishment of 3D PBS model, obtaining the ground-motion parameters of the bedrock face corresponding to a certain shear wave speed; (3) application of the trained ANNs to predict the ground-motion parameters on the ground surface, taking the simulated results and related site parameters as inputs, and the outputs are peak ground acceleration (PGA) and 5% damped spectral accelerations (Sa) at different periods on the ground surface. In this study, ANN models were trained on a strong-motion database based on Kiban–Kyoshin Network (KiK-net). After several verifications of the ANN predictions, a case study of the 21 October 2016 Mw6.2 Central Tottori earthquake was conducted. In addition to the comparison with observations, the broadband (0.1–10 Hz) results of the hybrid method were also compared with the results that obtained by transfer function based on recorded data and Next Generation Attenuation (NGA)-West2 ground-motion prediction equations (GMPEs) to demonstrate the effectiveness and applicability of the proposed method. In addition, the distribution of Sa for four periods in simulated area was presented. The performance of the hybrid method for predicting broadband ground-motion characteristics was generally satisfactory.

Multi‐input integrative neural network for soil seismic response modeling at KiK‐net downhole array sites

AbstractPrediction of the soil seismic response is of primary importance for geotechnical earthquake engineering. Conventional physics‐based models such as the finite element method (FEM) often face challenges due to inherent model assumptions and uncertainties of model parameters. Furthermore, these physics‐based models require significant computational resources, particularly when simulating seismic responses across numerous soil sites. In this study, a multi‐ input integrative neural network is developed for predicting soil seismic response based on the recorded data from a large number of downhole array sites. Ground motions, seismic event information, and wave velocity structures of the sites are utilized as input data in the proposed neural network, enabling the model to adapt to various site conditions. Comparative assessments against state‐of‐the‐art FEM models demonstrate that the proposed models exhibit superior prediction performance with increased efficiency. Furthermore, the pre‐training technique, a transfer learning method, is employed to predict the seismic response at new stations. By fine‐tuning the pre‐trained model derived from the extensive dataset with limited recorded data from new stations, high‐precision seismic response predictions can be realized, illustrating the adaptability and efficacy of the proposed approach in data‐scarce conditions.

Comparative Study of One-Dimensional Site Response Analysis on Deep Soft Clay Deposit using DEEPSOIL and NERA

Numerous high-rise buildings have been built in major cities in Indonesia. In high seismicity areas, such as Surabaya, the seismic behavior of structures is notably affected by the seismic characteristics of the subsurface soils. Typically, site-specific response analysis (SSRA) is conducted to determine the peak ground acceleration experienced at the ground surface. This paper compares one-dimensional site response analysis on deep soft clay deposits in Surabaya city using two commonly used 1D site response programs: DEEPSOIL and NERA (Non-linear Earthquake Site Response Analyse). A soil column model with 24 m thick very soft clay was developed. To represent different ground motion intensity, three levels of input motion were applied at the bedrock with peak ground accelerations (PGA) of 0.07g, 0.3g, and 0.51g. These input motions were then applied in a one-dimensional non-linear site response analysis to evaluate the seismic soil response at the surface. The evaluation involves examining the peak ground acceleration (PGA) and maximum shear strain profiles obtained from both software programs. The results indicate that the non-linear analysis conducted with NERA yielded greater amplification factors across all periods compared to the results obtained from DEEPSOIL. For the low-intensity motion, both software showed amplification of the input motion for all periods. In contrast, the spectral response obtained with DEEPSOIL demonstrated de-amplification trends for periods less than 1 s for the case of medium and high-intensity motions, whereas no de-amplification was observed from the results of NERA. This difference results in the amplification for medium and high-intensity motions can be attributed to the strength correction factors that are implemented in the DEEPSOIL software to take into account the representative shear strength of the soil layers.

2.5-dimension soil seismic response to oblique incident waves based on exact free-field solution

2.5-dimension soil seismic response to oblique incident waves based on exact free-field solution

A Comparative Analysis of Seismic Site Response in Time and Frequency Domains

This study aims primarily to perform a comparative analysis of the seismic response of a soil profile, in the time and frequency domains, in order to evaluate the seismic response of soil subjected to seismic excitation. After a few remarks made on the responses given by the linear elasticity method for this type of problem, it was considered necessary to use SHAKE 2000 and PLAXIS in this study. The obtained results were then compared with those of the available theoretical predictions. Rock elasticity, viscous damping and damping by hysteresis, and the nonlinearity of the ground were then taken into account. In addition, comparisons between recorded responses were also conducted.

Soil seismic response modeling of KiK-net downhole array sites with CNN and LSTM networks

Accurate prediction of soil seismic response is necessary for geotechnical engineering. The conventional physics-based models such as the finite element method (FEM) usually fail to obtain accurate predictions due to the model assumption and parameter uncertainties. And the physics-based models are computationally expensive. This study proposes deep learning models to develop data-driven surrogate models for the prediction of soil seismic response based on the recorded ground motions from KiK-net downhole array sites. Two kinds of advanced neural networks, convolution neural network (CNN) and long short-term memory (LSTM) neural network, are applied in this framework respectively. These models do not rely on any prior knowledge about the soil site. The performance of the deep learning models is demonstrated through both numerical and recorded examples. Compared with the state-of-art FEM models, the proposed models could achieve better prediction performance with higher efficiency. The average prediction error is reduced by more than 40% in time domain and 30% in frequency domain. Even though great variability exists during the propagation of seismic in the reality, the models can still get satisfactory predictions.

Multi-drive level Vibroseis test to evaluate the non-linear response of soft soils

In this paper we present the results of a seismic experiment using data produced by an active Vibroseis source and varying the drive force level, during a standard seismic reflection survey. We observed a clear non-linear response that can be linked to the presence of shallow soft sediment layers. The variation of the applied vibration force induces a change in both propagation velocity and attenuation of the Rayleigh waves, and this implies that such parameters are non-linear functions of the wave energy. We analyze the soil non-linear behavior with respect to the estimated induced strain, in order to compare the collected data against the observed reduction of shear modulus and damping values as usually measured in laboratory experiments and reported in the literature. The use of multi-component receivers allowed us also to identify the Rayleigh wave ellipticity and hence the resonance frequency of the studied site. Using active source data, rather than passive micro-tremors of unknown origin, for these applications is a novel approach. Thus, we propose an alternative and efficient method to characterize the non-linear key parameters of the soil seismic response, based on the use of controlled sources of widespread use in exploration seismics. This approach may pave the way to the development of utterly new site characterization techniques.

Application of discrete wavelet transform in seismic nonlinear analysis of soil–structure interaction problems

Simulation of soil–structure interaction (SSI) effects is a time-consuming and costly process. However, ignoring the influence of SSI on structural response may lead to inaccurate results, especially in the case of seismic nonlinear analysis. In this article, wavelet transform methodology has been utilized for investigation of the seismic response of soil–structure systems. For this purpose, different story outrigger-braced buildings resting on two different types of soil have been considered for SSI analysis. For each SSI system, several seismic records, with different values of peak ground acceleration (PGA) and peak ground velocity (PGV), have been first decomposed into approximate and detailed signals using a discrete wavelet transform. Then, seismic responses of the SSI systems subjected to the approximate signal have been evaluated. The results of the study show that, for earthquakes with low PGA/PGV ratio, the error percentage of all the parameters is smaller than 5% for the first level, and the error index is below 10% for the third level. As the PGA/PGV ratio of an earthquake increases, the concordance of approximate results with the main results decreases. However, even for the earthquakes with the PGA/PGV ratio higher than 1.2 g s/m, the first-level approximation can be used to predict seismic responses with at least 90% accuracy while significantly reducing the computational time.

Development of regional simulation of seismic ground‐motion and induced liquefaction enhanced by GPU computing

AbstractMuch research has been conducted for physics‐based ground‐motion simulation to reproduce seismic response of soil and structures precisely and to mitigate damages caused by earthquakes. We aimed at enabling physics‐based ground‐motion simulations of complex three‐dimensional (3D) models with multiple materials, such as a digital twin (high‐fidelity 3D model of the physical world that is constructed in cyberspace). To perform one case of such simulation requires high computational cost and it is necessary to perform a number of simulations for the estimation of parameters or consideration of the uncertainty of underground soil structure data. To overcome this problem, we proposed a fast simulation method using graphics processing unit computing that enables a simulation with small computational resources. We developed a finite‐element‐based method for large‐scale 3D seismic response analysis with small programming effort and high maintainability by using OpenACC, a directive‐based parallel programming model. A lower precision variable format was introduced to achieve further speeding up of the simulation. For an example usage of the developed method, we applied the developed method to soil liquefaction analysis and conducted two sets of simulations that compared the effect of countermeasures against soil liquefaction: grid‐form ground improvement to strengthen the earthquake resistance of existing houses and replacement of liquefiable backfill soil of river wharves for seismic reinforcement of the wharf structure. The developed method accelerates the simulation and enables us to quantitatively estimate the effect of countermeasures using the high‐fidelity 3D soil‐structure models on a small cluster of computers.

Effects of Groundwater Level on Seismic Response of Soil–Foundation Systems

AbstractA set of dynamic centrifuge experiments was performed to assess the effect of the depth of the groundwater table on the seismic site response and kinematic interaction of a foundation on un...

Lessons from April 6, 2009\u2009L\u2019Aquila earthquake to enhance microzoning studies in near-field urban areas

This study focuses on two weak points of the present procedure to carry out microzoning study in near-field areas: (1) the Ground Motion Prediction Equations (GMPEs), commonly used in the reference seismic hazard (RSH) assessment; (2) the ambient noise measurements to define the natural frequency of the near surface soils and the bedrock depth. The limitations of these approaches will be discussed throughout the paper based on the worldwide and Italian experiences performed after the 2009 L’Aquila earthquake and then confirmed by the most recent 2012 Emilia Romagna earthquake and the 2016–17 Central Italy seismic sequence. The critical issues faced are (A) the high variability of peak ground acceleration (PGA) values within the first 20–30 km far from the source which are not robustly interpolated by the GMPEs, (B) at the level 1 microzoning activity, the soil seismic response under strong motion shaking is characterized by microtremors’ horizontal to vertical spectral ratios (HVSR) according to Nakamura’s method. This latter technique is commonly applied not being fully compliant with the rules fixed by European scientists in 2004, after a 3-year project named Site EffectS assessment using AMbient Excitations (SESAME). Hereinafter, some “best practices” from recent Italian and International experiences of seismic hazard estimation and microzonation studies are reported in order to put forward two proposals: (a) to formulate site-specific GMPEs in near-field areas in terms of PGA and (b) to record microtremor measurements following accurately the SESAME advice in order to get robust and repeatable HVSR values and to limit their use to those geological contests that are actually horizontally layered.

Design and Commissioning of Continuous Soil Box Supported on Shake Tables Array for Testing Long Geostructures

The seismic soil response and soil-buried infrastructure interaction are of immense importance for the resilience of urban centres. Shake table testing offers an efficient tool for modeling the seismic soil-structure interaction. This paper presents the design and commissioning of a suspended continuum soil box supported on an array of shake tables to enable simulating homogeneity and inhomogeneity of soil and non-uniform seismic excitation of extended buried structures such as pipelines and tunnels. The large-scale shaking table model involves a steel box 7.3 m × 1.4 m × 1.2 m supported by 3 shake tables. It comprises 3 active rigid boxes (2 end boxes and one middle box) supported on 3 shaking tables and 2 passive (suspended) soft joint boxes to provide continuous soil medium. The continuous box design is modular and allows its expansion to be supported by the available 9 shaking tables for even much longer soil continuum model. The developed test setup was used to investigate the seismic response of free-field soil to verify the performance of the soil continuum box. The sand test model was instrumented with arrays of accelerometers embedded along its height within both rigid and suspended boxes to evaluate the effect of the test setup on the ground motion characteristics in both segments. Dynamic performance of the continuum box is examined by comparing the results of shaking table tests on the box empty and box containing a sand model. The results demonstrat that the soil box did not experience resonance with the sand model, hence it did not affect its response to the shaking. A quantitative analysis is conducted to evaluate the box boundary effects on the soil seismic response in terms of the L2-norm, μ, the acceleration time history waveform and Fourier spectrum characteristics at soil surface and 0.7m below surface. The consistency of surface peak acceleration under different seismic excitations and intensity levels are compared in terms of standard deviation, β. The results demonstrat that the developed suspended continuum model box performed well and can simulate the continuity and boundary conditions of free-field.

Peligro Sísmico por Efecto de Sitio en el Recinto Universitario Rubén Darío de la UNAN-Managua. Nicaragua

La presente investigación tiene como objetivo caracterizar el peligro sísmico por efecto de sitio en el área de la UNAN-Managua y está orientada a conocer las características y respuesta sísmica de los suelos en sus modos de vibrar ante un evento sísmico. El área de la UNAN-Managua corresponde a una zona de alta peligrosidad sísmica por localizarse al oeste una falla geológica activa, conocida como la Falla Zogaib, la cual tiene una longitud de 2.7 km y orientación norte-sur, y representa un peligro sísmico para la Ciudad Capital, que históricamente ha sido devastada por terremotos de magnitud moderada (Ms 6-6.2) originados por fallas geológicas, dejando daños en las infraestructuras provocando el colapso total de viviendas y edificaciones y la pérdida de vidas humanas en el país. La investigación es un aporte valioso para la UNAN-Managua y es de base para la planificación de fututos proyectos de construcción en el recinto universitario para la prevención de desastres por terremotos y aporta información para la reducción del riesgo sísmico en área. El estudio se llevó a cabo como un proyecto de investigación titulado “Estudio de efecto de sitio en la UNAN-Managua”, que se realizó con el apoyo económico de los Fondos para proyectos de investigación (FPI) de la UNAN-Managua.

Laboratory Tests for Subgrade Reaction Coefficient in Seismic Design of Underground Engineering Domain

Subgrade reaction coefficient is commonly considered as the primary challenge in simplified seismic design of underground structures. Carrying out test is the most reliable way to acquire this intrinsic soil property. Owing to the limitations of experimental cost, time consumption, soil deformation mode, size effect, and confined condition, the existing testing methods cannot satisfy the requirements of high‐precision subgrade reaction coefficient in seismic design process of underground structures. Accordingly, the present study makes an attempt to provide new laboratory testing methods considering realistic seismic response of soil, based on shaking table test and quasistatic test. Conventional shaking table test for sandy free‐field was performed, with the results indicating that the equivalent normal subgrade reaction coefficients derived from the experimental hysteretic curves are reasonable and verifying the deformation mode under seismic excitation. A novel multifunctional quasistatic pushover device was invented, which can simulate the most unfavorable deformation mode of soil during the earthquake. In addition, the first successful application of an innovative quasistatic testing method in evaluating subgrade reaction coefficient was reported. The findings of this study provide preliminary detailed insights into subgrade reaction coefficient evaluation which can benefit seismic design of underground structures.

Determination of ground motion parameters by seismic response analysis method of soil layer

In this paper, the factors affecting the results of seismic response analysis of soil layers are analyzed by substituting trial calculation for various factors in the engineering example of seismic safety evaluation. In the soil response analysis of building site, the lithology of overburden soil, the sudden change of soil structure (interlayer) and the input shear wave value all have influence on the soil seismic response. Among them, the weak interlayer has significant influence on the peak acceleration and characteristic periodic value of seismic response analysis, while the hard interlayer, simple overburden and the type of bedrock soil have little influence on the seismic response of soil. The following construction projects must be evaluated for seismic safety:(1) Major State construction projects; (2) Construction projects that may cause floods, fires, explosions, massive leakage of highly toxic or highly corrosive substances or other serious secondary disasters after being damaged by earthquakes, including reservoir dams, dikes, oil and gas storage, and storage of inflammable, explosive, highly toxic or highly corrosive substances. Facilities and other construction projects that may cause serious secondary disasters; (3) nuclear power plants and facilities that may cause radioactive pollution after earthquake damage; (4) other construction projects that provinces, autonomous regions and municipalities directly under the Central Government consider to be of great value or have significant impact on their respective administrative regions.

Nonlinear Numerical Simulation of the Soil Seismic Response to the 2012 Mw 5.9 Emilia Earthquake Considering the Variability of the Water Table Position

Nonlinear Numerical Simulation of the Soil Seismic Response to the 2012 Mw 5.9 Emilia Earthquake Considering the Variability of the Water Table Position

Seismic soil response of scaled geotechnical test model on small shaking table

This research comprises a series of shaking table tests and finite element analyses of scaled soil-foundation model to determine the dynamic interaction effects between the foundation and the underlying soil. The purpose of this work is to specify a realistic geometric scaling coefficient for test model to be used in a small-capacity shaking table. The scaling factor addressed in this study involves not only geometric similarity but also kinematic and dynamic similarity with the real system. The free-field soil response under different earthquake excitations for both real system and scaled test model was directly performed by using 2D finite element method under plane-strain conditions. The kinematic interaction of the shallow foundation slab on free-field motion was also examined. In this computational model, the behavior of the soil medium is idealized by linear elastic-perfectly plastic assumption with a yield surface according to Mohr-Coulomb failure criterion. Two different earthquake acceleration records as Chi-Chi (1999) and Loma Prieta (1989) have been carried out at the bedrock level of the soil-foundation system for this study. By comparing the results of the numerical analysis with data from the laboratory tests, the proposed geotechnical model can properly simulate the seismic response of the full-scale real system. It can be concluded that the kinematic interaction effects are negligible in the low frequencies. It should be noted that the local soil properties have considerably amplified the earthquake response of the free-field motions in comparison to the bedrock excitations.

Experimental study on seismic response of underground tunnel-soil-surface structure interaction system

More and more projects of underground structures undercrossing adjacent surface structures have emerged in recent years. The existence of underground structure influences the propagation of seismic wave, and the inertia effect of the surface structure affects both the seismic response of surrounding site and that of underground structures. Thus, the underground structure and near surface structure can be deem as an interaction system. In this paper, in order to investigate the law of seismic response of underground structure-soil-surface structure interaction system, a shaking table model test was designed and implemented. Based on the experimental results, the law of seismic response of such complex system was analyzed. Note that to overcome the limitation of the bearing capacity of shaking table and eliminate the distortion of soil-structure rigidity ratio, the sawdust soil was chosen to model the surrounding site soil. Test results showed that using sawdust soil as a model soil is feasible. Regarding the law of seismic response of interaction system, it was found that the existence of the tunnel structure has weakened the rigidity of the whole model, and therefore, the seismic response of surrounding soil was amplified. However, it was observed that the existence of the tunnel impeded the propagation of seismic wave to some extent and thus reduced the seismic response of the surface structure, especially for lower and medium floors. The existence of surface structure suppressed the seismic response of soil and underground structures. By comparing the test results under different earthquake excitations, it was shown that the seismic response of the system was affected by the type of seismic wave significantly.

Effect of specimen preparation techniques on dynamic properties of unsaturated fine-grained soil at high suctions

The seismic response of soil depends on proper evaluation and use of soil dynamic properties, including shear modulus and damping ratio at various strain levels. Despite extensive studies on the shear modulus and damping ratio of saturated soils, research on the dynamic properties of unsaturated fine-grained soils — especially at high suction — is limited. This study aims to investigate the dynamic properties of loess at a variety of initial states resulting from different specimen preparation techniques (reconstituted, recompacted, and intact) and their evolutions due to suction-induced desiccation. Results of resonant column tests show that at initial states, the specimen preparation technique has a negligible effect on the normalized modulus (G/Gmax) and damping degradation pattern, while the influence becomes significant at a high suction (40 MPa). This is attributed to the microstructural evolution of specimens with different initial states that were subjected to suction-induced desiccation. More specifically, the elastic shear strain threshold decreases (reduction of elastic range) while shear modulus increases as suction reaches 40 MPa. Furthermore, the rate of increase in the damping ratio as well as degradation of the shear modulus for specimens at high suction is faster than their initial states. Based on the scanning electron microscopy observations, these findings may be attributed to the aggregation of larger silt–clay assemblies induced by suction increase. Consequently, soil with larger aggregates behaves more like granular sandy soil than saturated silt or clay.