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.

This paper establishes a novel full-process numerical simulation framework for analyzing the 3D seismic response of mountain tunnels induced by active faults. The framework employs a two-step approach to achieve wavefield transmission through equivalent seismic load: first, a highly efficient and accurate FMIBEM (Fast multipole indirect boundary element method) is used for large-scale 3D numerical simulations at the regional scale to generate broadband ground motions (1-5 Hz) for specific sites; subsequently, using the FEM (Finite element method), a refined simulation of the plastic deformation of surrounding rock and the elastoplastic behavior of the tunnel structure was conducted at the engineering scale. The accuracy of the framework has been validated. To further demonstrate its effectiveness, the framework is applied to analyze the impact of different fault movement mechanisms on the damage to mountain tunnels based on a scenario earthquake (Mw 6.7). By introducing tunnel structure damage classification and corresponding damage indicators, the structural damage levels of tunnels subjected to active fault movements are quantitatively evaluated. The findings demonstrate that the framework successfully simulates the entire process, from fault rupture and terrain amplification to the seismic response of tunnel structures. Furthermore, the severity of tunnel damage caused by different fault types is ranked as follows: reverse fault > normal fault > strike-slip fault.

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.

The flexible joints and segmental lining serve as effective seismic measures for tunnel in high-intensity seismic area. However, the tunnel axial deformation at flexible joints has not been fully incorporated into analytical models. This study presents a novel mechanical model for flexible joints that considers tension (compression)shear-rotation deformations, replacing the traditional shear-rotation springs model. An improved semi-analytical solution has been developed for the longitudinal response of a tunnel featuring a three-way flexible joint mechanical model subjected to fault movement. The nonlinear elastic-plastic foundation spring, the soil-lining tangential interaction, and the axial force of tunnel lining have been considered to improve the applicability and precision of proposed method. The proposed solution is compared with existing models, such as short beams connected by shear and rotation springs, by examining the predictions against numerical simulations. The results indicate that the predictions of the proposed model align much more closely with the outcomes of the numerical simulations than those of the existing models. For the working conditions selected in 4, neglecting the tension-compression deformation at flexible joints an 81.8% error in the peak axial force of the tunnel and a 20.2% error in the peak bending moment. The reason is that ignoring the axial deformation of these joints results in a larger calculated axial force on the lining, which subsequently leads to increased bending moment and shear force. Finally, a parameter sensitivity analysis is conducted to investigate the effect of various factors, including flexible joint stiffness, segmental lining length, and the length of the tunnel fortification zone.

In earthquake-prone areas, mountain tunnels often suffer from seismic damage when traversing active fault zones. To capture the seismic behavior of mountain tunnel under the action of active faults motion, the rate and state friction (RSF) relation is introduced to define the stick-slip dynamic behavior of a fault. The RSF relation is implemented in the finite element methods (FEMs). Numerical simulations of triaxial patch tests indicate that the RSF method can effectively capture the stick-slip dynamics. To reproduce the seismic damage to Daliang tunnel caused by slip of the Lenglongling fault, a three-dimensional (3D) numerical model including tunnel structure and plates of the fault is established. Seismic waves triggered by fault slip are then reproduced using the model. The simulation results show that the waves are dissipated while travelling and that their amplitudes decrease with depth. The failure of the tunnel lining is captured, and its seismic responses, including the displacement and strain of the structure, are extracted for various fault strike angles. The simulations are consistent with the observations, and it indicates that the movement of the simulated tunnel structure adjacent to the fault surface is significantly greater than those in the foot wall and in the middle of the fault. This study has the potential to provide a more direct means of understanding the seismic action of infrastructure induced by earthquakes. Seismic waves are no longer needed as input to the numerical simulation and instead, the earthquakes are generated by directly modeling the stick-slip motion of the fault. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The presence of underground structures within fault zones has the potential to alter deformation patterns on the ground surface, thereby placing existing structures-typically regarded as safe-at risk. This paper presents findings from four centrifuge model tests and 3D numerical simulations exploring the effects of tunneling in fault zones. This study investigated the values associated with foundation rotation, surface deformations, and the patterns of fault rupture propagation through various soil strata. The results demonstrate that the presence of a tunnel alters the interaction pattern between fault rupture and foundation systems, which can lead to an increase in foundation rotation. Notably, the findings indicate that a precise consideration of superstructure shape can enhance foundation rotation by up to 23%. Furthermore, the presence of a tunnel in the fault zone causes substructures to endure major damage from vertical fault displacements exceeding 0.6 m. In contrast, these substructures experienced similar levels of damage at vertical fault displacements of 1.7 m in the absence of tunnels.

Safety assessment of ductile iron (DI) pipelines under fault rupture is a crucial aspect for underground pipeline design. Previous studies delved into the response of DI pipelines to strike-slip faults, but all existing theoretical methods for DI pipelines under strike-slip faults are not suitable for normal fault conditions due to the difference in soil resistance distribution. In this study, analytical solutions considering asymmetric soil resistance and pipe deflection are developed to analyze the behavior of DI pipelines under normal faulting. Results indicate that DI pipelines with a longer segment length are more vulnerable to pipe bending damage, while exhibiting a lower sensitivity to joint rotation failure. For the conditions of pipe segment length L = 1.5 m at all burial depths and L = 3 m at a shallow burial depth, when the fault-pipe crossing position shifts from a joint to a quarter of the segment length (rp = 0 similar to 0.25), DI pipelines are more prone to joint rotation failure. However, in the cases of L = 3 m at a moderate to deep burial depth and L = 6 m at all burial depths, the most unfavorable position is rp = 0.75, dominated by the mode of pipe bending failure.

The main causes of damage include poor site selection, such as building on fault lines or on fill soil, as well as deficiencies in design, materials, and workmanship. Damage levels are also linked to the economic conditions of the region. In the 1939 earthquake, there were high casualties due to the magnitude of the earthquake, lack of engineering design in traditional structures and unsuitable soil conditions. Similarly, in the 1992 earthquake, unexpected damage occurred due to faulty designs created by inexperienced engineers who lacked sufficient knowledge of the seismic behavior of structures, errors in craftsmanship and workmanship, and unsuitable residential area selection for construction. These problems continue today and put most of the building stock at risk in case of a major earthquake. Seismic steel isolators are used in two new buildings in the city; if they are effective, they should be made mandatory in new construction. Otherwise, consideration should be given to relocating the city to the more stable southern rocky areas, which were unaffected in both 1939 and 1992.

To study the dynamic response rules of pile foundations of mega-bridges over faults in strong seismic areas, a finite element model of the pile foundation-soil-fault interaction of the Haiwen Bridge is established. The 0.2-0.6 g peak acceleration of the 5010 seismic waves is input to study the effect of the seismic wave of different intensities and the distance changes between the fault and the pile foundation on the dynamic response of the pile body. The results show that the soil layer covering the bedrock amplifies the peak pile acceleration, and the amplifying effect decreases with increasing seismic wave intensity. However, bedrock has less of an effect on peak acceleration. The relative pile displacement shows the mechanical properties of elastic long piles. The pile foundation generates a large bending moment at the bedrock face and the upper soil layer interface, and a large shear force at the pile top and the soft-hard soil body interface. The relative displacement, bending, and shear bearing characteristics of the pile foundations on the upper and lower plates of the fault are significantly different. The deformation characteristics are affected by faults in a region ten times the pile diameter. Analysis of the dynamic p-y curves shows that the soil resistance on the pile side of the lower plate at the same depth is greater than that of the upper plate. Sensitivity of the dynamic response of pile foundations on either side of the fault to the effects of seismic intensity and distance between the pile foundation and the fault: distance l > seismic intensity q.

The cyclic injection and production of fluids into and from underground gas storage (UGS) may lead to caprock failure, such as capillary sealing failure, hydraulic fracturing, shear failure, and fault slipping or dilation. The dynamic sealing capacity of a caprock-fault system is a critical constraint for safe operation, and is a key factor in determining the maximum operating pressure (MOP). This study proposed an efficient semi-analytical method for calculating changes in the in situ stress within the caprock. Next, the parameters of dynamic pore pressure, in situ stresses, and deformations obtained from reservoir simulations and geomechanical modeling were used for inputs for the analytical solution. Based on the calculated results, an experimental scheme for the coupled cyclic stress-permeability testing of caprock was designed. The stability analysis indicated that the caprock was not prone to fatigue shear failure under the current injection and production strategy, supported by the experimental results. The experimental results further reveal that the sealing capacity of caprock plugs may remain stable. This phenomenon is attributed to cyclic stress causing pore connectivity and microcrack initiation in certain plugs, while leading to pore compaction in others. A comparison between the dynamic pore pressure and the minimum principal stress suggests that the risk of tensile failure is extremely low. Furthermore, although the faults remain stable under the current injection and production strategies, the continuous increase in injection pressure may lead to an increased tendency for fault slip and dilation, which can cause fault slip ultimately. The MOPs corresponding to each failure mode were calculated. The minimum value of approximately 36.5 MPa at capillary sealing failure indicated that the gas breakthrough in the caprock occurred earlier than rock failure. Therefore, this minimum value can be used as the MOP for the target UGS. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).