This study examines the failure mechanisms of offshore caisson-type composite breakwaters (OCCBs) under seismic loading through 1g shaking table model tests, comparing cases with and without remediation measures against seabed soil liquefaction. For this purpose, several countermeasures are implemented, comprising wraparound geogrid inclusions within the rubble mound layer, stone columns and compacted improvement zones in the seabed soil, all aimed at enhancing the seismic resilience and stability of OCCBs. Six physical model tests are conducted to evaluate the effectiveness of the applied remediation measures in minimizing liquefactioninduced deformations of OCCBs, including settlement, lateral movement, and tilting. Experimental findings indicate that the caisson settlement is primarily caused by the lateral flow of the foundation soil and the rubble mound layer. The combined use of stone columns and wraparound geogrid reinforcements efficiently mitigates this lateral flow. Notably, remediating just 2.8 % of the liquefiable seabed soil with stone columns decreases OCCB settlement and tilting by 45.4 % and 31 %, respectively, compared to the non-remediated model. Additionally, incorporating wraparound geogrid reinforcements within the rubble mound layer results in even further reductions of settlement and tilting by 90.6 % and 91.3 %, respectively. This research offers valuable insights for developing effective countermeasures to mitigate seismic-induced damage to OCCBs seated on liquefiable seabed soils.

This study investigates the liquefaction characteristics of deep soil layers and their subsequent effects on the seismic response of subway station structures, utilizing shaking table tests and inputting seismic waves of varying principal frequencies. Macroscopically, the liquefaction of deep soil strata does not result in surface manifestations such as water spraying and sand bubbling. However, it still induces cracking and damage to the soil surrounding the structure. Analyzing from the perspective of the pore pressure ratio reveals that the ratio under free-field conditions is significantly lower than under structural conditions. Additionally, the pore pressure ratio caused by the Beijing Hotel wave is greater, followed by the Beijing artificial wave, while the Ming Shan wave results in the smallest ratio. In terms of the station structure, the structural acceleration and tensile strain increment induced by the Beijing Hotel wave are the most significant, followed by the Beijing artificial wave, with the least effect from the Ming Shan wave. This indicates that the liquefaction behavior of deep soil layers is primarily influenced by the overlying load and the frequency characteristics of seismic waves. The construction of subway stations reduces the overlying loads on soil layers, increasing the likelihood of soil layer liquefaction. Meanwhile, a lower main frequency of the seismic wave results in a higher degree of liquefaction in the deep soil layers. The seismic response of the station structure is contingent on the frequency characteristics of the seismic wave. The lower the primary frequency of the seismic wave, the higher the seismic response of the station structure. Furthermore, the liquefaction behavior of the deep soil layers also impacts the seismic response of the station structure, particularly the tensile strain response of the top and bottom slabs of the station structure.

Resonance can significantly amplify a structure's response to seismic loads, leading to extended damage, especially in critical infrastructure like nuclear power plants. Thus, this study focuses on the resonance effects of the dynamic interaction between layered soil, pile foundations, and nuclear island structures, which is particularly important given the limited availability of bedrock sites for such facilities. Specifically, this study explores the resonance behavior of nuclear islands under various seismic conditions through large-scale shaking table tests by developing a dynamic interaction model for layered soil-pile-nuclear island systems. The proposed model comprises a 3 x 3 pile group supporting the upper structure of a nuclear island embedded within a three-layer soil profile. Sinusoidal waves of varying frequencies identify the factors influencing the system's resonance response. Besides, the resonance effects are validated by inputting seismic motions based on compressed acceleration time histories. Furthermore, the impact of non-primary frequency components on structural resonance is assessed by comparing sinusoidal wave components. The findings reveal that resonance effects increase as the amplitude of the input seismic motion increases to a certain threshold, after which the effect stabilizes. This trend is particularly pronounced in the bending moment response at the pile head. Additionally, an independent resonance phenomenon is observed in the superstructure, suggesting that its resonance effects should be considered separately in nuclear island design. Similar resonance effects are observed when the predominant frequency of sinusoidal waves closely matches the compressed seismic motions, suggesting that sinusoidal inputs effectively simulate structural resonance during seismic design testing.

Coral sand, as a geological material for foundation filling, is widely used for reclamation projects in coral reef areas. The coral sand is characterized by a wide grain size distribution. A series of centrifuge shaking table tests were conducted to explore the seismic response of a shallow buried underground structure in saturated coral sand and coral gravelly sand. The emphasis was placed on comparing the similarities and differences in the dynamic behavior of the underground structure at the two sites. The responses of excess pore pressure, acceleration, displacement, and dynamic soil pressure of the structure were analyzed in detail. The results indicated that the underground structure in coral sand had a significant influence on the development of excess pore pressure in the surrounding soil, but this effect was not evident in coral gravelly sand due to well-drained channels. Liquefaction was observed in the soil layer around the structure in coral sand, but it did not occur in coral gravelly sand. In coral sand, the liquefaction of the soil layer at the bottom of the structure caused a significant attenuation in the acceleration of the structure. Compared to coral gravelly sand, the acceleration response of the soil layer near the bottom of the underground structure was higher in coral sand. During the shaking, the displacement pattern of the structure in coral gravelly sand was slight subsidence-slight upliftsignificant subsidence, while it exhibited a significant uplift in coral sand. The maximum dynamic soil pressure distribution on the structural sidewalls presented a trapezoidal distribution, and the dynamic soil pressure had a strong connection with the development of excess pore pressure in the surrounding soil.

Deciding on the inclusion of tiers and determining the optimal number of tiers are critical considerations in the design of reinforced soil retaining walls (RSRWs). In this study, the mechanical properties of RSRWs under seismic loading are discussed in depth, with special attention paid to the influence of tiered configuration effects on the seismic performance of RSRWs. The response characteristics of these structures under seismic loading were comparatively analyzed by conducting shaking table tests of single-tiered, two-tiered, and three-tiered modular geogrid RSRWs. The results show that localized modular misalignment mainly occurs at the top of the retaining walls of all tiers, and reasonable tiered design can enhance the stability, but too many tiers may instead reduce the structural stability. The tiered reinforced soil retaining walls (TRSRWs) exhibit higher natural frequencies and damping ratios, which increase with more tiers, and the natural frequencies and damping ratios of the upper-tiered walls are always higher than those of the lower-tiered walls. The acceleration amplification effect is more significant in the upper part of the retaining wall structure, and the tiered design can reduce the acceleration amplification effect to a certain extent, but the increase in the number of tiers does not have much effect on this. The horizontal displacement of the TRSRWs shows the distribution of upper large and lower small, and the two-tiered retaining wall effectively reduces the horizontal displacement of the wall facing, whereas the three-tiered retaining wall does not have a significant improvement effect. The tiered design significantly optimizes the settlement of the retaining walls, and the number of tiers has little effect on the settlement improvement. The seismic active soil pressure increased with the peak ground acceleration and loading frequency, and the tiered design changed its distribution, and the increase in the number of tiers helped to further reduce the soil pressure. The increment of reinforcement strain in TRSRWs was lower than that in single-tiered retaining walls, and the tiered design effectively reduced the reinforcement stress, but the number of tiers had a limited effect on the improvement of this effect. The upper part of the wall in the un-tiered design is prone to overall tilt and horizontal expansion, and the deformation of the upper-tiered walls of the TRSRWs is all in a composite deformation mode, while the lowest-tiered walls are in a single deformation mode. The tiered design has a positive effect in limiting the development of potential failure surfaces in the substructure, resulting in improved stability of the substructure. The results of the study can provide a reference for the design selection of RSRWs.

Local site conditions may pose a significant influence on the seismic responses of submarine pipelines by altering both the offshore motion propagation and soil-structure interaction (SSI). This paper aims to provide an in-depth understanding of the influence regularity of local site conditions on the seismic performance of free-spanning submarine pipelines (FSSPs). For this purpose, a suite of underwater shaking table tests were performed to investigate the seismic responses of FSSP subjected to the offshore spatial motions at three site categories. Response comparison factor (chi R.ij${\chi }_{R.ij}$) is defined to quantify the structural response discrepancies caused by the seismic inputs at different sites. The test results indicate that responses of the studied model FSSP gradually increase as spatial offshore motions at softer soil sites are employed as inputs; and the values of chi R.ij${\chi }_{R.ij}$ vary with a maximum magnitude of up to 40%-60% for different response indices when the site soil changes from fine sand to clay. Subsequently, the corresponding numerical simulations are carried out to reproduce the seismic responses of the test model. The experimental and numerical results meet a good agreement, indicating that the developed numerical modeling method can accurately predict the seismic responses of FSSPs. Following this verified modeling method and using the p-y approach to address the SSI effect, fragility surfaces of the studied FSSP are derived in terms of PGA and site parameter VS30${V}_{S30}$ (shear-wave velocity in the top 30 m of the soil profile) via probabilistic seismic demand analyses. The impact of local site conditions on the seismic performance of the FSSP is quantitatively examined by comparing the fragility curves corresponding to various VS30${V}_{S30}$. Furthermore, a fast seismic damage assessment method is proposed for efficiently evaluating the performance of FSSPs buried in various offshore soil conditions. This approach proves beneficial for designers and decision-makers, enabling accurate estimation of seismic damage and facilitating the implementation of post-earthquake maintenance measures for FSSPs.

Burial depth is a crucial factor affecting the forces and deformation of tunnels during earthquakes. One key issue is a lack of understanding of the effect of a change in the buried depth of a single-side tunnel on the seismic response of a double-tunnel system. In this study, shaking table tests were designed and performed based on a tunnel under construction in Dalian, China. Numerical models were established using the equivalent linear method combined with ABAQUS finite element software to analyze the seismic response of the interacting system. The results showed that the amplification coefficient of the soil acceleration did not change evidently with the burial depth of the new tunnel but decreased as the seismic amplitude increased. In addition, the existing tunnel acceleration, earth pressure, and internal force were hardly affected by the change in the burial depth; for the new tunnel, the acceleration and internal force decreased as the burial depth increased, while the earth pressure increased. This shows that the earth pressure distribution in a double-tunnel system is relatively complex and mainly concentrated on the arch spandrel and arch springing of the relative area. Overall, when the horizontal clearance between the center of the two tunnels was more than twice the sum of the radius of the outer edges of the two tunnels, the change in the burial depth of the new tunnel had little effect on the existing one, and the tunnel structure was deemed safe. These results provide a preliminary understanding and reference for the seismic performance of a double-tunnel system.

In this study, a series of shaking table model tests were performed to evaluate the dynamic earth pressure acting on pile foundation during liquefaction. The dynamic earth pressure acting on piles were evaluated with depth and pile diameters comparing with excess pore water pressure, it means that the kinematic load effect plays a substantial role in dynamic pile behavior during liquefaction. The dynamic earth pressure acting on pile foundations with mass exhibited significant similarity to those without upper mass. Analyzing the non-fluctuating and fluctuating components of both excess pore water pressure and dynamic earth pressure revealed that the non-fluctuating component has a dominant influence. In case of non-fluctuating component, dynamic earth pressure is larger than excess porewater pressure at same depth, and the difference increased with depth and pile diameter. However, in the case of the fluctuating component, the earth pressure tended to be smaller than the excess pore water pressure as the depth increased. Based on the results of a series of studies, it can be concluded that the dynamic earth pressure acting on the pile foundation during liquefaction is applied up to 1.5 times the excess pore water pressure for the non-fluctuating component and 0.75 times the excess pore water pressure for the fluctuating component.

The tall building construction sector has recently exhibited an increasing development, especially in Europe. This activity is aligned with European policies regarding soil conservation and social housing. Due to their slenderness, such structures are particularly sensitive to wind and earthquake loads. Nevertheless, current building codes, standards, and most scientific literature neglect the interaction of these events as simultaneity has always been considered a rare design case due to the limited effect on the structural elements. The present work carries out a careful statistical investigation on the occurrence of strong earthquakes accompanied by a wind load event, characterized by non-negligible daily mean-wind velocities in Italy, where more than onethird of its area is occupied by high mountains, limiting the urban development to confined zones. Subsequently, the effect of the simultaneous occurrence of earthquake and wind loads has been studied, both from the numerical and experimental points of view (i.e., shaking table and wind tunnel tests) to evaluate the consequences on structural and non-structural elements (e.g., fa & ccedil;ades) of a building case study. Results show that the cumulative effect of typical and noncatastrophic daily mean wind velocity (i.e., in the range of 5-10 m/s at 10 m from the ground) and a typical and non-catastrophic seismic daily shock (i.e., with magnitude in the range of 3-5), can trigger large inter-story drift ratio values and fatigue, causing damage to non-structural elements - like fa & ccedil;ades - and consequently a risk for occupants and high economic losses.

Considering the engineering background of the dangerous western mountain railroad, large-scale shaking table model experiments were conducted on embankment slopes supported by single and double-row piles, subjected to El-Centro wave excitations. Based on parameters such as displacement and acceleration, an in-depth investigation was conducted to study the differences in dynamic response characteristics between the two slope models. Moreover, the reasons for the differences between the two slopes were explored using fast Fourier transform (FFT) spectra. The results revealed that both the support effect and the differences in anti-slip piles gradually increased with the increase in the input wave amplitude. At input wave amplitudes of 0.1g-0.3g, both single and double-row pile slopes remained stable, with minimal differences in their overall dynamic response characteristics. However, at an input wave amplitude of 0.4g, significant differences in the dynamic responses of both slopes emerged. Macroscopic damage was more apparent in the single-row pile slope, with high slope surface displacement, accumulated soil damage, and noticeable nonlinear characteristics. At an input wave amplitude of 0.5g-0.6g, both slope models exhibited a pronounced elevation effect in the peak ground acceleration (PGA) amplification factor. Additionally, plastic zones were observed on the road cut face and behind the piles in both models. The presence of retaining piles effectively suppressed the upward trend of PGA amplification coefficients along the slope and prevented the connection of plastic zones on the slope surface. Notably, the PGA amplification effect of the single-row pile slope was pronounced, with a wide and deep plastic zone, severe local instability, and relatively weak seismic support effect. The introduction of the FFT spectral ratio revealed that the difference in amplitude amplification effects of single and double-row pile slopes in the 5-10 Hz band was the main reason for the difference in their dynamic responses. Under seismic loading, the failure process of the single-row pile-supported slope involved three stages: initial stability of the slope, plastic deformation of the slope surface soil, and local collapse and disintegration of the slope. In contrast, the double-row pile-supported slope experienced the first two stages of this failure process.