Immersed tunnels are typically built in areas subjected to ground motion. Therefore, an evaluation of the seismic performance of the soil-tunnel system is essential. A series of shaking-table tests was conducted to study the influences of the site soil and overlying water layer on the seismic responses of soil deposits and an immersed tunnel. Detailed information on the experiment setup is provided with special focus on the similitude relationship, fabrication of the model system, measurement setup, and loading procedures for a simulation of the seismic waves. Three groups of tests at different sites in dry sand, saturated sand, and saturated sand with an overlying water layer were carried out using the same seismic excitations. The seismic responses of the soil deposits and the dynamic responses of the tunnel model were obtained. The experiment results indicate that, when considering only horizontal earthquake excitations, soil liquefaction significantly influences the propagation of seismic waves and the dynamic responses of the tunnel, whereas the water layer has no obvious effects on the dynamic performance of the ground or tunnel. Furthermore, the acceleration responses of the tunnel elements were analyzed qualitatively, and the joints are deemed important elements in an antiseismic immersed tunnel design.

To study the dynamic response of a saturated sand-underground structure system subjected to earthquakes, a series of shaking table tests with a geometric scale ratio of 1/30 were conducted. Based on the experimental acceleration records of testing soil deposits, the relationship between dynamic shear stress and horizontal soil displacement was analyzed by the 1D shear beam inverse calculation method. Meanwhile, the development law of the equivalent dynamic horizontal subgrade reaction coefficient and the dynamic strain of the sidewall in the underground structure has also been discussed. The testing results indicate that the dynamic shear stress of the soil deposit under the bottom plate of the underground structure is larger than that of the soils surrounding the sidewall and above the roof plate; in addition, the soil displacement tends to decrease with the buried depth. The dynamic shear stress–displacement hysteretic loop of the soil deposits tends to be plump as the input amplitude increases. The spectral characteristics of ground motions obviously influence both the dynamic shear stress–displacement hysteretic curve and the excess pore water pressure ratio of saturated sand soil, especially under medium and strong excitations. The equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of soil depth, and the difference between the coefficient above and underneath the underground structure model can reach 7.589 MN/m³. On the contrary, the equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of the input amplitude of ground motions, and the maximum reduction ratios of the coefficient are 74.4%, 66.7%, and 47.3%, corresponding to the El-Centro, Kobe, and Wolong ground motions, respectively. The soil liquefaction has a certain effect on the equivalent dynamic horizontal subgrade reaction coefficient. In general, the dynamic strain at the top of the sidewall in the underground structure is higher than that at the bottom of the sidewall, which illustrates that the deformation of underground structures is in good agreement with the seismic deformation mode of soil deposits.

Shear keys are usually installed as crucial shear-resistant members of an immersion joint; thus, the mechanical behavior of the shear keys, especially under earthquake loading, deserves more attention. This paper presents a novel arc-shaped energy absorption device developed for shear keys. In order to verify the seismic performance of shear keys strengthened by the arc-shaped energy absorption devices, a series of pseudo-static tests were conducted, in which different axial pressures (300 kN, 400 kN) were also taken into consideration. The testing results indicated that failure mode of the shear key enhanced by the energy absorption devices was a synthesis of the oblique shear failure of the rubber blankets, the buckling of the energy absorption devices, and the concrete fracture of the shear key. In view of load-displacement hysteretic curves of testing specimens, loops of the reinforced shear keys were plumper than those from a traditional shear key. In addition, the load-bearing capacity (cracking load, yield load, peak load, and failing load) differences of the shear keys with and without energy absorption devices reinforcement under the same axial pressure were 33.0%, 36.7%, 26.0%, and 23.6%, respectively. The maximum equivalent viscous coefficient values of the shear keys with and without energy absorption devices reinforcement were 0.37, 0.38, and 0.32, respectively. The arc-shaped energy absorption devices can contribute to the hysteretic behavior of the shear keys. However, the axial pressure had a positive influence on the load bearing capacity, accumulated energy absorption capacity, and initial stiffness of the shear keys. In contrast to that, the axial pressure had negative influence on ductility ratio of the reinforced shear keys (equivalent viscous coefficient values of two enhanced shear keys were roughly equal). A reasonable stiffness scheme of an energy absorption device should be given attention during the anti-seismic design of an immersion joint. The study can provide scientific support for further study on the seismic responses of immersion joints and promote the application of earthquake control technology in immersed tunnels.

This study employed a modified elastoplastic constitutive model that can systematically describe the monotonic and cyclic mechanical behaviors of typical marine soils combining the subloading, normal, and superloading yield surfaces, in the seismic response analysis of three-dimensional (3D) marine site. New evolution equations for stress-induced anisotropy development and the change in the overconsolidation of soils were proposed. This model can describe the unified behaviour of unsaturated soil and saturated soil using independent state variables and can uniquely describe the multiple mechanical properties of soils under general stress states, without changing the parameter values using the transform stress method. An effective stress-based, fully coupled, explicit finite element–finite difference method was established based on this model and three-phase field theory. A finite deformation analysis was presented by introducing the Green-Naghdi rate tensor. The simulation and analysis indicated that the proposed method was sufficient for simulating the seismic disaster process of 3D marine sites. The results suggested that the ground motion intensity would increase due to the local uneven complex topography and site effect and also provided the temporal and spatial distribution of landslide and collapse at the specific location of the marine site.

Buildings close to the ground treated by the resonance- free vibratory hammer method are often vulnerable to excessive vibrations. An in situ test of an urban soft site was carried out to investigate the resonance-free vibratory hammer induced vibration effects during construction. Vibration pickups were set at the positions with distances of 15 m, 30 m, 50 m, and 100 m away from the vibration source. On the basis of the results obtained from this investigation, vibration effects of the resonance-free vibratory hammer and safe construction distances were systematically analyzed. The testing results indicate that the vibration in the vertical direction is stronger than that in the other two horizontal directions. The vertical vibration should be the main reference quantity for the foundation treatment by using the resonance-free vibratory hammer method. The predominant frequency of each measuring point in the same direction decreased with an increase of the distance from the vibration source (DFTVS). In terms of the measuring point with a DFTVS of 30 m, the peak values of velocity in all directions were within 5 mm/s, which meet the requirements of the allowable limit of building vibration. According to the in situ testing results, a model for calculating the acceleration exponent of the vibration caused by the resonance-free vibratory hammer technology was established by comprehensively considering the amplitude of acceleration, the attenuation coefficient of THE DFTVS, and the vibration correction factor. Finally, the reliability of the calculation model was verified through the comparison between the calculated results and field vibration experimental results, in which all the correlation coefficients of validation example were above 0.9.

The arrangement scheme of the sensors in a pseudo static test for an immersed tunnel joint was revealed in this paper. To achieve this target, the pushover analysis of the two immersion joint models were studied by using numerical calculation. The mechanical characteristics of the immersed tunnel joint under horizontal loading condition were carefully observed. According to the numerical results, shear keys and connecting part in tunnel elements are the key observation sections, the stress development, the shear capacity and the deformation features of the immersion joint should be measured. Furthermore, a loading system of pseudo static test for immersion joint is also developed. Based on the loading system and numerical funding, the locations for deploying sensors were determined. The scheme of sensor positions played a crucial role in guaranteeing the successful completement of the experiment, and also can offer some reference opinions for similar experiments.