Numerical methods with high accuracy and low computational cost are needed to predict the dynamic response of the ground during earthquakes. Conventional dynamic analysis methods include explicit and implicit methods, whereas explicit methods are often numerically unstable and have large errors, and implicit methods require a large cost to solve the simultaneous equations. We propose a new method that is explicit but more accurate than the implicit method and can allow for large time increments based on the analytical solution to the semi-discretized finite element equations. The wave kernel function (WKF) is known as a spectral representation of the exact solution of the one-dimensional wave equation. The proposed method combines WKF and digital filtering techniques for time semi-discretized finite element equations. Since the WKF amplifies spurious high frequencies due to spatial discretization errors, a low-pass filter is incorporated into the WKF. This new method is referred to as the time-spectral finite element method (T-S FEM) in this work. The numerical solution of the 1D wave equation was obtained by T-S FEM; even a numerical solution in close agreement with the exact ones was obtained even when a large time increment corresponding to Courant number 2.0 was employed. Furthermore, the results suggest that the optimal cutoff frequency of the low-pass filter is approximately equal to the time update frequency

This study develops a fully explicit high-performance solid-fluid coupled dynamic analysis method for soil liquefaction using the GEOSX platform, a high-performance simulation framework for modeling geomechanics problems. The method is explicitly coupled, with the solid phase solved by explicit FEM and fluid phase solved by explicit FVM. The CycLiq constitutive model is implemented for simulating sand liquefaction behavior. The accuracy, efficiency, and applicability of this method is evaluated via simulation of the 1D consolidation problem and LEAP-2017 centrifuge shaking table tests. Dynamic simulations of a rockfill dam on and thick liquefiable deposit with different resolutions are conducted, to evaluate the efficiency and scalability of the FEM-FVM solid-fluid coupled dynamic analysis method.

In this study, the effect of the enclosed air contained in unsaturated soil on the cyclic shear was investigated numerically. First, the governing equation of unsaturated cyclic triaxial test was developed based on the mass balance equations and constitutive equations with consideration of the enclosed air. Then, the series of numerical simulations were performed to clarify the effect of the change of mass between enclosed air and continue air, and the existence of enclosed air before starting cyclic loading. The simulated results showed that the consideration of the enclosed air affected the behavior of the suction, the pore water and the air. Finally, the simulations aimed to the unsaturated cyclic triaxial test showed the good agreement with the experiment in the point of view of reproducing the tendency of decrease of the suction.

This paper presents Ta-Ger constitutive model for clays that has been implemented in the finite difference codes FLAC and FLAC3D. The model is based on a theoretical framework in multiaxial space combining perfect plasticity with Bouc-Wen-type smooth hysteresis through the formulation of an explicit elastoplastic matrix, which is able to provide a continuous function between input (displacement, strain etc) and output (force, stresses etc). This plasticity framework was originally proposed by Tasiopoulou and Gerolymos (2016a) and was used to develop Ta-Ger constitutive model for sands (Tasiopoulou and Gerolymos, 2016a,b; Tasiopoulou et al., 2019, 2021). In this paper, the same framework is used to develop Ta-Ger constitutive model for soils with clay-like behavior under monotonic and cyclic loading. The fundamental capabilities of capturing clay-like behaviour are illustrated through element-level comparisons of the calibrated model with monotonic and cyclic laboratory tests conducted on near-normally and overconsolidated clays from Izmit Bay, Türkiye. Key aspects of clay response captured by the model include: i) monotonic hardening, ii) strain-dependent hysteretic responses at different shear strain levels in terms of realistic stress-strain loops, secant shear modulus and strength, iii) strain-dependent shear modulus degradation and hysteretic damping, iv) strain-dependent cyclic degradation as a function of the number of loading cycles, v) post-peak shear strength decrease to a residual value with increasing shear strain, vi) ratcheting caused by asymmetric loading. The paper also presents system-level validation against centrifuge tests simulating the seismic wave propagation through soft, normally consolidated clays encountered in the San Francisco Bay under strong shaking inducing significant nonlinearity.

The cyclic loading response of sand is of particular importance for many branches of engineering practices including earthquake engineering. This work presents a simple constitutive model that considers the key mechanical characteristics of cyclically loaded sand, including the dependence on initial stress level and void ratio, as well as past stress history. For this purpose, a two-surface modeling scheme is adopted by combining a rotating yield surface and an expanding bounding surface. The latter evolves with plastic deformations and memorizes past stress history. Both hardening rule and plastic flow rule are functions of state parameters to account for the dependence of strength and dilatancy on void ratio and confining stresses. The enhanced contraction and stiffness degradation following plastic dilation are considered. The model performance is evaluated against laboratory tests of this study and reported in the literature. We also utilize the model to explore the effects of past stress history on the monotonic and cyclic loading response of sand.

Advanced constitutive models can be used to simulate the effects of soil liquefaction on foundations and buildings in dynamic Finite Element analyses. While various constitutive models have been applied in numerical studies considering one-time cyclic loading, there remains a need to investigate their performance for repeated cyclic loading events. Deposits in seismic areas are likely to be subjected to multiple consecutive earthquakes and aftershocks. However, the impact of the previous shaking history on the cyclic resistance of the soil and its post-liquefaction static response is the subject of ongoing research and is not yet fully understood. Based on findings from experimental studies, this paper presents an assessment of a constitutive model and its ability to capture the effects of the loading history on the sand response. This involves the simulation of laboratory element tests for different cyclic loading, re-consolidation and monotonic shearing series. A particular focus lies on model features incorporated to simulate cyclic mobility at low effective stress levels, as well as the anisotropic post-liquefaction response of the material.

Easy accessibility and affordability of railways over the other mode of transportation makes it most preferred mode of transportation. High speed trains are major technical innovation in the railway industry which has reduced the travel time. As the speed is increasing day by day, numbers of problems are increasing. Ground vibration is one of the concerns which can result in derailment and deterioration of track embankment system. The ground vibration may be detrimental to the stability and safety of the rail track system as well as of the nearby structures. When the running speed of the train matches with the Rayleigh wave velocity of the sub soil “Critical Condition” occurs due to which vibrations get amplified. Soft soils can amplify the induced ground vibration as their Rayleigh wave velocity is very close to the operating speed range of high-speed trains. Field investigation to measure train induced vibrations is expensive, therefore numerical modelling is necessary to predict these vibration. In this study, finite element modelling has been done to study the ground vibration generated at railway track embankment system in soft soils. For this purpose, railway embankment as specified by Research Design and Standards Organization (RDSO) is modelled using finite elements. Peak particle velocity is measured at different depths of embankment. Further parametric study has been done to find the effect of increase in train speed and increase in soil stiffness.