Ensuring the accuracy of free-field inversion is crucial in determining seismic excitation for soil-structure interaction (SSI) systems. Due to the spherical and cylindrical diffusion properties of body waves and surface waves, the near-fault zone presents distinct free-field responses compared to the far-fault zone. Consequently, existing far-fault free-field inversion techniques are insufficient for providing accurate seismic excitation for SSI systems within the near-fault zone. To address this limitation, a tailored near-fault free-field inversion method based on a multi-objective optimization algorithm is proposed in this study. The proposed method establishes an inversion framework for both spherical body waves and cylindrical surface waves and then transforms the overdetermined problem in inversion process into an optimization problem. Within the multi-objective optimization model, objective functions are formulated by minimizing the three-component waveform differences between the observation point and the delayed reference point. Additionally, constraint conditions are determined based on the attenuation property of propagating seismic waves. The accuracy of the proposed method is then verified through near-fault wave motion characteristics and validated against real downhole recordings. Finally, the application of the proposed method is investigated, with emphasis on examining the impulsive property of underground motions and analyzing the seismic responses of SSI systems. The results show that the proposed method refines the theoretical framework of near-fault inversion and accurately restores the free-field characteristics, particularly the impulsive features of near-fault motions, thereby providing reliable excitation for seismic response assessments of SSI systems.

In this study, the effect of near-field and far-field ground motions on the seismic response of the soil pile system is investigated. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field and far-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layer soil, liquefiable sand layer over dense sand, and the pile is utilized. Modeling is conducted in FLAC 3D software. The P2P Sand constitutive model is selected for sandy soil. Three fault-normal near-field and three far-field ground motion records were applied to the model. The numerical results show that near field velocity pulses have a considerable effect on the system behavior and sudden huge displacement demands were observed. Also, during the near-field ground motions, the exceeded pore water pressure coefficient (Ru) increases so that liquefaction occurs in the upper loose sand layer. Due to the pulse-like ground motions, a pulse-like relative displacement is created in response to the pile. Meanwhile the relative displacement response of the pile is entirely different due to the energy distribution during the far-field ground motions.

The cyclic behavior of clay significantly influences the dynamic response of offshore wind turbines (OWTs). This study presents a practical bounding surface model capable of describing both cyclic shakedown and cyclic degradation. The model is characterized by a simple theoretical framework and a limited number of parameters, and it has been numerically implemented in ABAQUS through a user-defined material (UMAT) subroutine. The yield surface remains fixed at the origin with isotropic hardening, while a movable projection center is introduced to capture cyclic hysteresis behavior. Cumulative plastic deviatoric strain is integrated into the plastic modulus to represent cyclic accumulation. Validation against undrained cyclic tests on three types of clay demonstrates its capability in reproducing stress-strain hysteresis, cyclic shakedown, and cyclic degradation. Additionally, its effectiveness in solving finite element boundary value problems is verified through centrifuge tests on large-diameter monopiles. Furthermore, the model is adopted to analyze the dynamic response of monopile OWTs under seismic loading. The results indicate that, compared to cyclic shakedown, cyclic degradation leads to a progressive reduction in soil stiffness, which diminishes acceleration amplification, increases settlement accumulation, and results in higher residual excess pore pressure with greater fluctuation. Despite its advantages, this model requires a priori specification of the sign of the plastic modulus parameter cd to capture either cyclic degradation or shakedown behavior. Furthermore, under undrained conditions, the model leads pstabilization of the effective stress path, which subsequently results in underestimation of the excess pore pressure.

Iron pipes connected by bell-spigot joints are utilized in buried pipeline systems for urban water and gas supply networks. The joints are the weak points of buried iron pipelines, which are particularly vulnerable to damage from excessive axial opening during seismic motion. The axial joint opening, resulting from the relative soil displacement surrounding the pipeline, is an important indicator for the seismic response of buried iron pipelines. The spatial variability of soil properties has a significant influence on the seismic response of the site soil, which subsequently affects the seismic response of the buried iron pipeline. In this study, two-dimensional finite element models of a generic site with explicit consideration of random soil properties and random mechanical properties of pipeline joints were established to investigate the seismic response of the site soil and the buried pipeline, respectively. The numerical results show that with consideration of the spatial variability of soil properties, the maximum axial opening of pipeline joints increases by at least 61.7 %, compared to the deterministic case. Moreover, in the case considering the variability of pipeline-soil interactions and joint resistance, the spatial variability of soil properties remains the dominant factor influencing the seismic response of buried iron pipelines.

Fiber reinforcement has been demonstrated to mitigate soil liquefaction, making it a promising approach for enhancing the seismic resilience of tunnels in liquefiable strata. This study investigates the seismic response of a tunnel embedded in a liquefiable foundation locally improved with carbon fibers (CFs). Consolidated undrained (CU), consolidated drained (CD), and undrained cyclic triaxial (UCT) tests were conducted to determine the optimal CFs parameters, identifying a fiber length of 10 mm and a volume content of 1 % as the most effective. A series of shake table tests were performed to evaluate the effects of CFs reinforcement on excess pore water pressure (EPWP), acceleration, displacement, and deformation characteristics of both the tunnel and surrounding soil. The results indicate that CFs reinforcement significantly alters soil-tunnel interaction dynamics. It effectively mitigates liquefaction by enhancing soil stability and slowing EPWP accumulation. Ground heave is reduced by 10 %, while tunnel uplift deformation decreases by 61 %, demonstrating the stabilizing effect of CFs on soil deformation. The fibers network interconnects soil particles, improving overall structural integrity. However, the increased shear strength and stiffness due to CFs reinforcement amplify acceleration responses and intensify soil-structure interaction, leading to more pronounced tunnel deformation compared to the unimproved case. Nevertheless, the maximum tunnel deformation remains within 3 mm (0.5 % of the tunnel diameter), posing no significant structural risk from the perspective of the experimental model. These findings provide valuable insights into the application of fibers reinforcement for improving tunnel stability in liquefiable foundations.

A series of large-scale shaking table tests were conducted to investigate the dynamic response and damage characteristics of the variable- single pile foundation in liquefiable soil-rock interaction strata under seismic loading. The test results show that the seismic responses of the excess pore pressure ratio under seismic excitations are divided into four stages, among which the difference in the sustained liquefaction stage is the most significant. Pile acceleration amplification is governed by dual coupling effects of soil-pile interaction and structural stiffness. The pile body bending moment distribution features dual-peak characteristics, the largest peak arises at the soil layers interface, while the other peak occurs at the variable-section. Increased seismic excitation accelerates the liquefaction of the saturated sand layer, yet simultaneously slows down the dissipation of the excess pore pressure. As the seismic excitation increases, the acceleration response and displacement response of the pile top are most significant, though maximum bending moment positions remain stable. The stress overrun damage occurs gradually in the variable- zone under strong earthquakes. Based on the analysis results and the Fourier spectrum modal characteristics of the pile top, the damage mechanism of the pile body is revealed and verified. This study will provide an essential reference for further understanding the seismic response and damage of the variable- single pile foundation in liquefiable soil-rock interaction strata.

Based on the deficiencies of the generalized response displacement method and the integral response displacement method for longitudinal seismic analysis of the shield tunnel, the dynamic sub-str1cture analysis method for longitudinal seismic response of a large-diameter shield tunnel crossing the complex soil layer is proposed. The feasibility and superiority of the dynamic sub-structure analysis method are explored by comparing it with the calculation results of the three-dimensional (3D) soil-underground structure interaction model. Then, a finite element refined 3D model of the 2.7 km Suai submarine shield tunnel is established by using the proposed method, and the longitudinal seismic response of the large-diameter shield tunnel crossing complex soil layers is simulated and analyzed. The research results indicate that the proposed dynamic sub-structure method has clear concepts, accurate calculation results and high efficiency to simulate the dynamic soil-tunnel interaction, which can avoid the error effect of the equivalent soil spring used in the generalized response displacement method. At the same time, this method can consider the seismic effect of the complex soil layers which has been avoided by the generalized response displacement method and the integral response displacement method. Also, the calculation results by the proposed method can comprehensively present the typical earthquake damages of shield tunnels crossing the wide river valley or the strait. It proves that it is not appropriate to simplify the longitudinally of the shield tunnel into a straight line, as doing so would neglect the influence of the longitudinal slope of complex river valleys or the straits. Also, the longitudinal seismic response of the shield tunnel is more sensitive to low-frequency seismic waves and the bolts are more susceptible to seismic damage compared to the segment opening.

This study investigated the impact of soil-structure interaction on the seismic performance of masonry ancient pagodas. For this purpose, shaking table tests were conducted using a pagoda model to simulate the seismic damage patterns and damage evolution of the pagoda under conditions considering soil-structure interaction. Additionally, numerical models were established for both rigid foundation conditions and soil-structure interaction conditions, validated through dynamic characteristic testing and shaking table experiments. The results indicated that under soil-structure interaction conditions, the top of the pagoda cracked first, with severe damage occurring on the second floor. The damage characteristics of the pagoda differ significantly from those observed under rigid foundation conditions. The numerical simulations effectively predicted the dynamic response of the structure. Compared to the results obtained under rigid foundation conditions, the acceleration of the upper structure decreased by 34 %-79 % after considering soil-structure interaction, while the horizontal displacement at the top of the pagoda increased by 1.4 mm-7.8 mm. The inter-story displacement angle of the first floor was amplified by 3-10 times, with significant degradation of stiffness, while the impact on the stiffness of the top floor was relatively minor. The tensile damage to the pagoda was more pronounced, and the damage area shifted from the first floor to the second floor. The findings provide important references for the seismic assessment of masonry ancient pagodas.

This paper proposes a frequency wavenumber-finite element hybrid method with kinetic source model for dynamic analysis of pile founded nuclear island from fault to structure. This method benefits from the effective synthesis of broadband ground motions by the fault source model, the realism of frequency wavenumber for earthquake simulation from fault to the site and the mesh refinement capabilities of the finite element in modeling the nuclear structure and the near soil. This method achieves the expression of source rupture, wave propagation, site response, soil-structure interaction, soil nonlinearity and structure response accurately, which solves the multi-scale problem from crustal layer to nuclear structure. Under finite-fault excitation, the correctness of the proposed method is validated by comparing with the frequency wavenumber method. Then, a full process seismic simulation of a pile founded nuclear island built on a non-rock site is conducted. The influence of source parameter and soil-structure interaction is studied. Results indicate that the change of source parameter can lead to difference nuclear island failure direction. With the increase of dip angle, the appearance of maximum stress is in advance. The soil nonlinearity could greatly amplify the soil-structure interaction effect and the loads on piles. The connection between the containment vessel and the raft is vulnerable and the piles on the edge of the raft is prone to damage. This hybrid method could accomplish an appropriate seismic evaluation of the nuclear structures and the conclusions may provide reference for seismic design of nuclear structure.

To address the challenge of the complex and extensive seismic design elements of tunnels, which are difficult to be accurately described using mathematical functions, a novel model combining convolutional neural networks (CNN), gated recurrent units (GRU), and an attention mechanism is proposed. Firstly, based on actual engineering examples, the tunnel dimensions and site soil information are determined to establish a numerical model of tunnel seismic response and verify its reliability. Then, the soil parameters, seismic motion amplitude, tunnel depth, and overlying water depth are selected for systematic analysis of the displacement momentum (DM) and time of maximum damage occurrence (TMDO). The parameters with higher influence are chosen as input variables, while the calculated DM and TMDO from the reliable numerical model are selected as the output variables to be predicted. Next, integrating the GRU model to capture long-term dependencies in time series, the CNN model to extract spatial features, and the attention mechanism to handle complex relationships among multiple variables, the CNN-GRU-Attention prediction model was established. By generating dataset samples through numerical simulation, accurate predictions of DM and TMDO were achieved. Finally, using the proposed model to establish the objective function relationship between input and output parameters, employing the NonDominated Sorting Genetic Algorithm II (NSGA-II) to find the optimal input design features, achieving the optimal design of tunnel seismic performance. The results show that: (1) The calculation results of the numerical model for tunnel seismic response conform to general research findings, indicating sufficient reliability. (2) The error compensation and dynamic updating mechanisms improved prediction accuracy. The R2 values for the training set reach 0.973 and 0.982 respectively. (3) Optimizing DM and TMDO using the NSGA-II algorithm leads to a 23.42% reduction in DM and a 18.71% increase in TMDO. After optimization, tunnel displacement is reduced, damage is delayed, and seismic performance is significantly improved.