This paper proposes a carbon fiber reinforced polymer (CFRP) retrofitting scheme for improving the seismic performance of atrium-style metro stations (AMS). Past experimental studies have confirmed that the weakest of the AMS during strong earthquakes is located at the upper-story beam ends. However, there is thus far no candidate for a reference approach to retrofitting and strengthening the AMS. This study addresses this gap by applying CFRP retrofitting to both ends of the upper-story beam. The main objective is to assess the effectiveness of the proposed retrofitting scheme. First, a three-dimensional finite element model is developed to simulate dynamic soil-AMS interaction. The validity of the numerical method is assessed via a comparison with measured data from reduced-scale model tests. Second, a numerical model of the AMS retrofitted with CFRP is built using validated methods. Finally, dynamic time-history analyses of the AMS with and without CFRP retrofitting are conducted, and their dynamic responses, including inter-story drift, dynamic strain, and tensile damage, in conjunction with the lateral displacement of the surrounding ground, are compared. Comparison of the results for the non-retrofitted and retrofitted structures shows that CFRP retrofitting significantly reduces both the principal strains and tensile damage factors at the upper-story beam ends while slightly increasing those values at the mid-span of the beam; additionally, it does not change the structural lateral deformation. Therefore, it can be concluded that CFRP retrofitting could effectively improve the seismic performance of the AMS without changing its lateral stiffness.

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.

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.

The seismic response of tunnels in liquefiable ground requires careful consideration of adjacent structures due to potential structure-soil-structure interaction (SSSI) effects. These interactions can significantly influence the behaviour of underground systems during earthquakes, potentially affecting structural integrity and safety. This study aims at explore the interaction effect of a large diameter shield tunnel and a shallow-buried station with rectangular under seismic motion in liquefiable ground. For this purpose, 1 g shaking table tests of model SSSI system is designed. The model shield tunnel was manufactured with segments and joints using plexiglass, while the model rectangular station was precast using concrete embedded at a shallow layer adjacent to the tunnel. The responses of excess pore water pressure (EPWP), acceleration, displacement of the foundation in SSSI system and deformation of shield tunnel were measured and analysed in detail. The influence of relative stiffness of different structures is discussed based on finite element method. The experimental results show that the SSSI system exhibited a certain nonlinearity and plastic damage under input motions. Shear stress from two sides of the model structures caused the soil to dilate, resulting in a reduced EPWPR build-up between the two structures. Attenuation of the high-frequency components in the seismic wave was also observed in the soil between two structures. The tunnel structure exhibited a vertical stretching deformation at around 15 degrees angle from the vertical direction. The soil beneath the station has compensated for the soil loss caused by the uplift of the model tunnel during the process of tunnel uplift under input motion with high GPA. These new findings in the case of SSSI is helpful for the design and construction of underground structures.

The biocemented coral sand pile composite foundation represents an innovative foundation improvement technology, utilizing Microbially Induced Carbonate Precipitation (MICP) to consolidate a specific volume of coral sand within the foundation into piles with defined strength, thereby enabling them to collaboratively bear external loads with the surrounding unconsolidated coral sand. In this study, a series of shaking table model tests were conducted to explore the dynamic response of the biocemented coral sand pile composite foundation under varying seismic wave types and peak accelerations. The surface macroscopic phenomena, excess pore water pressure ratio, acceleration response, and vertical settlement were measured and analysed in detail. Test results show that seismic wave types play a decisive role in the macroscopic surface phenomena and the response of the excess pore water pressure ratio. The cumulative settlement of the upper structure under the action of Taft waves was about 1.5 times that of El Centro waves and Kobe waves. The most pronounced liquefaction phenomena were recorded under the Taft wave, followed by the El Centro wave, and subsequently the Kobe wave. An observed positive correlation was established between the liquefaction phenomenon and the Aristotelian intensity of the seismic waves. However, variations in seismic wave types exerted minimal influence on the acceleration amplification factor of the coral sand foundation. Analysis of the acceleration amplification factor revealed a triphasic pattern-initially increasing, subsequently decreasing, and finally increasing again-as burial depth increased, in relation to the peak value of the input acceleration. This study confirms that the biocemented coral sand pile composite foundation can effectively enhance the liquefaction resistance of coral sand foundations.

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.

Composite reinforcement concrete square piles exhibit excellent bending resistance and deformation capacity, along with construction advantages such as ease of transportation. In recent years, they have been widely adopted in building pile foundation applications. However, their seismic behavior, particularly under multi-directional excitation, remains inadequately explored. This study employs large-scale shaking table tests to evaluate the seismic response of a single composite reinforcement square pile embedded in a soft clay foundation under different horizontal excitations (0 degrees and 45 degrees) and two distinct ground motions (Wenchuan Songpan and Chi-Chi) to assess directional anisotropy and resonance effects, with explicit consideration of soil-structure interaction (SSI). The key findings include the following: the dynamic earth pressure along the pile exhibits a distribution pattern of large at the top, small at the middle and bottom. And SSI reduced pile-soil compression by 20-30% under 45 degrees excitation compared to 0 degrees. The dynamic strain in outer longitudinal reinforcement in pile corners increased by 30-60% under 45 degrees excitation compared to 0 degrees. Under seismic excitation considering SSI, the bending moment along the pile exhibited an upper-middle maximum pattern, peaking at depths of 3-5 times the pile diameter. Axial forces peaked at the pile head and decreased with depth. While bending moment responses were consistent between 0 degrees and 45 degrees excitations, axial forces under 45 degrees loading were marginally greater than those under 0 degrees. The Chi-Chi motion induced a bending moment about four times greater than the Songpan motion, highlighting the resonance risks when the ground motion frequencies align with the pile-soil system's fundamental frequency.

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.

Liquefied landslide disasters induced by earthquake are serious, in order to solve the problem of support and management of slopes with liquefiable soil layer, a novel anti-slide pile to prevent liquefaction is proposed based on the concept of combination of prevention and resistance, which integrates active drainage and passive anti-slip. To evaluate the effectiveness of the novel anti-slide pile in preventing liquefaction, a slope model was developed based on survey data from slopes with liquefiable soil layers in the upper Yellow River region. A large-scale shaking table model test was conducted to compare the novel anti-slide pile with conventional ones. The failure mode and dynamic response characteristics of excess pore water pressure in soil of the slope with liquefiable soil layer supported by different types of anti-slide piles under earthquake are obtained. The results indicate that the failure mode of slope with liquefied soil layer supported by anti-slide pile under earthquake is earthquake-induced-horizontal ejection of overlying soil layer on liquefied soil layer-bulging, shearing of slope surface at the bottom of liquefied soil layer-flowing and sliding accumulation of soil in front of anti-slide pile. In comparison to conventional anti-slide piles, the novel anti-slide pile for liquefaction prevention can rapidly and efficiently dissipate excess pore pressure in the surrounding soil. This mechanism effectively prevents liquefaction around the pile, achieving the goal of liquefaction prevention. The research findings confirm the reliability of the novel anti-slide pile for liquefaction prevention, providing valuable insights for mitigating seismic liquefaction landslide disasters.