Accurate prediction of ground-surface settlement adjacent to an excavation is often difficult to achieve without using accurate representation of small-strain nonlinearity in a soil model within ...finite-element analyses. In this paper a simplified semiempirical model is proposed for predicting maximum wall deflection, maximum surface settlement, and surface-settlement profile due to excavations in soft to medium clays. A large number of artificial data are generated through finite-element analyses using a well-calibrated, small-strain soil model. These data, consisting of wall displacements and ground-surface settlements in simulated excavations in soft to medium clays, provide the basis for developing the proposed semiempirical model. The proposed model is verified using case histories not used in the development of the model. The study shows that the developed model can accurately predict maximum wall deflection and ground-surface settlement caused by braced excavations in soft to medium clays.
•A State-of-the-art review on the seismic response and design of tunnels is presented.•Emphasis is placed on recorded responses of actual tunnels during past earthquakes.•Relevant recent experimental ...and numerical studies are discussed.
The paper presents a state-of-the-art review of the current understanding of the seismic behaviour of tunnels. Emphasis is placed on recorded responses of actual tunnels during past earthquakes, as well as relevant experimental studies. In particular, the observed seismic performance of tunnels is initially discussed, by providing cases of reported damage during past earthquakes. This is followed by a review of the current monitoring systems for this infrastructure, which can be used to create future case studies based on actual recordings of the seismic response. Subsequently, the paper provides a summary of relevant experimental studies that took place in the centrifuge or on shaking tables, followed by a short discussion of current analytical models, simplified methods and numerical schemes for the seismic analysis and vulnerability assessment of tunnels. Throughout the presentation, the current overall gaps in understanding the seismic response of tunnels are identified in an attempt to stimulate further work in these areas by the research community.
A new simulation-based site amplification model for shallow sites with thickness less than 30 m in Korea is developed. The site amplification model consists of linear and nonlinear components that ...are developed from one-dimensional linear and nonlinear site response analyses. A suite of measured shear wave velocity profiles is used to develop corresponding randomized profiles. A VS30 scaled linear amplification model and a model dependent on both VS30 and site period are developed. The proposed linear models compare well with the amplification equations developed for the western United States (WUS) at short periods but show a distinct curved bump between 0.1 and 0.5 s that corresponds to the range of site natural periods of shallow sites. The response at periods longer than 0.5 s is demonstrated to be lower than those of the WUS models. The functional form widely used in both WUS and central and eastern North America (CENA), for the nonlinear component of the site amplification model, is employed in this study. The slope of the proposed nonlinear component with respect to the input motion intensity is demonstrated to be higher than those of both the WUS and CENA models, particularly for soft sites with VS30 <300 m/s and at periods shorter than 0.2 s. The nonlinear component deviates from the models for generic sites even at low ground motion intensities. The comparisons highlight the uniqueness of the amplification characteristics of shallow sites that a generic site amplification model is unable to capture.
This study investigates the conditions for which one-dimensional (1-D) nonlinear (NL) site response analysis results are distinct from equivalent-linear (EL) results and provides guidance for ...predicting when differences are large enough to be of practical significance. Relative differences in spectral accelerations and Fourier amplitudes computed from NL and EL analyses are assessed for a range of site conditions and for suites of input motions appropriate for active crustal and stable continental regions. Among several considered parameters, EL/NL differences are most clearly dependent on shear strain index (Iγ), defined as the ratio of input motion peak velocity to time-averaged shear-wave velocity in the top 30 m of the soil profile. For small Iγ (generally under 0.03%), EL and NL results are practically identical, whereas at larger strains, differences can be significant for frequencies >0.3 Hz. Frequency-dependent Iγ values are recommended for conditions above which NL analyses are preferred to EL.
This article presents a suite of response spectrum (RS) and Fourier amplitude spectrum (FAS) site amplification models for Central and Eastern North America (CENA). The amplification database used in ...model development was produced through large-scale one-dimensional site response analyses and overcomes limitations of prior databases by providing broader coverage of anticipated site conditions. New amplification functions conditioned on either VS30 or site natural period (Tnat) as the primary independent variable are provided, the latter of which better captures features of the computed site amplification from the simulated database (i.e. model dispersion is reduced). Models for standard deviation also are developed. RS and FAS linear amplification functions that adjust the reference condition of VS = 3000 m/s to VS30 = 760 m/s, and account for amplification for profiles either with a sharp VS impedance or a more gradual increase in VS are also developed.
Seismic design of water retaining structures relies heavily on the response of the retained water to shaking. The water dynamic response has been evaluated by means of analytical, numerical, and ...experimental approaches. In practice, it is common to use simplified code‐based methods to evaluate the added demands imposed by water sloshing. Yet, such methods were developed with an inherent set of assumptions that might limit their application. Alternatively, numerical modeling methods offer a more accurate way of quantifying the water response and have been commonly validated using 1 g shake table experiments. In this study, a unique series of five centrifuge tests was conducted with the goal of investigating the hydrodynamic behavior of water by varying its height and length. Moreover, sine wave and earthquake motions were applied to examine the water response at different types and levels of excitation. Arbitrary Lagrangian‐Eulerian finite element models were then developed to reproduce 1 g shake table experiments available in the literature in addition to the centrifuge tests conducted in this study. The results of the numerical simulations as well as the simplified and analytical methods were compared to the experimental measurements, in terms of free surface elevation and hydrodynamic pressures, to evaluate their applicability and limitations. The comparison showed that the numerical models were able to reasonably capture the water response of all configurations both under earthquake and sine wave motions. The analytical solutions performed well except for cases with resonance under harmonic motions. As for the simplified methods, they provided acceptable results for the peak responses under earthquake motions. However, under sine wave motions, where convective sloshing is significant, they underpredict the response. Also, beyond peak ground accelerations of 0.5 g., a mild nonlinear increase in peak dynamic pressures was measured which deviates from assumed linear response in the simplified methods. The study confirmed the reliability of numerical models in capturing water dynamic responses, demonstrating their broad applicability for use in complex problems of fluid‐structure‐soil interaction.
Pore-water pressure (PWP) generation can lead to soil softening and liquefaction of sandy soils during earthquakes, with potential influence on site response and seismic design. The authors evaluated ...the generalized quadratic/hyperbolic (GQ/H) constitutive model, which captures small-strain stiffness, large-strain shear strength, and is coupled with a widely used cyclic strain–based PWP generation model (termed GQ/H+u). A suite of cyclic direct simple shear tests with a range of relative densities (∼30%–80%) and effective vertical stresses (∼25–200 kPa) and dynamic centrifuge tests with liquefiable sands were used to evaluate the ability of the GQ/H+u model to simulate cyclic soil behavior. Results indicate that GQ/H+u provides reasonable estimates of PWP increase during cyclic shear, with differences between measured and computed excess PWP ratios (r
u
) for both element and centrifuge tests generally smaller than 0.1. Computed spectral accelerations are comparable to centrifuge test measurements, with almost no bias at medium to long periods (T > 0.4 s) when the computed maximum shear strain (γ
max
) was smaller than the limit shear strain (γ
limit
). When computed r
u
> 0.8 and computed γ
max
> γ
limit
, spectral accelerations may be underestimated at both short and long periods as dilative behavior is not captured by GQ/H+u.
Downhole arrays provide enhanced understanding of dynamic soil behavior and site response. Historically, downhole array recordings have been available only for earthquakes with relatively limited ...durations. New recordings from a number of KiK-net downhole arrays during the 11 March 2011, Mw 9.0, subduction zone earthquake near the east coast of Honshu, Japan, allow us to investigate dynamic soil characteristics and site response due to long-duration subduction zone earthquakes. Using these recordings, we perform one-dimensional site response analyses to evaluate the applicability of commonly used analysis approaches under long-duration earthquakes. We find that site response analyses capture key features of measured surface response spectra particularly at soft rock/stiff soil sites subject to long-duration motion. However, at softer soil sites, it appears that the modulus reduction is overestimated and site-specific characterization is needed.
The United States Geological Survey national seismic hazard maps have historically been produced for a reference site condition of VS30 = 760 m/s. For other site conditions, site factors are used, ...which heretofore have been developed using ground motion data and simulations for shallow earthquakes in active tectonic regions. Research results from the Next Generation Attenuation-East (NGA-East) project, as well as previous and contemporaneous related research, demonstrate different levels of site amplification in central and eastern North America (CENA) as compared to active regions. We provide recommendations for modeling of ergodic site amplification in CENA based primarily on research results from the literature. The recommended model has three additive terms in natural logarithmic units. Two describe linear site amplification: an empirically constrained VS30-scaling term relative to a 760 m/s reference and a simulation-based term to adjust site amplification from the 760 m/s reference to the CENA reference of VS = 3000 m/s. The third term is a nonlinear model that is described in a companion document. All median model components are accompanied by epistemic uncertainty models.
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