Adjacent tunnel construction and environmental disturbances can lead to longitudinal deformation in pipe-jacking tunnels. The longitudinal deformation of the tunnel is closely related to the occurrence of joint dislocation, joint opening, and other defects. In view of the difficulty of obtaining 3D longitudinal deformation curves, a method is proposed to obtain 3D longitudinal deformation curves based on a large number of 3D point cloud data with high spatial resolution and large spatial dimensions. Combined with the mechanism of defects occurrence, a theoretical basis for tunnel defects assessment based on tunnel longitudinal deformation is proposed. Taking one pipe jacking tunnel as an example, the longitudinal settlement curve and the 3D longitudinal deformation curve are compared. The correlation between the 3D longitudinal deformation curve and defects such as mud leakage, cracks, and differential deformation is illustrated from the perspective of three indexes: deformation amount, bending deformation, and shearing deformation. The accuracy and reliability of the 3D longitudinal deformation curve in tunnel defects detection and assessment are verified.

The maintenance of in-service shield tunnel lining has become a critical issue in recent decades due to the rapid development of the metro system in China. The external load is one of the most important factors influencing the deformation and performance of the in-service shield tunnels. It is hard to evaluate the external load since it is influenced by complex factors. And the arbitrary-distributed external load is not considered in the existing theories. A novel back-analysis approach for evaluating the external load using the deformation of tunnel lining was proposed based on Betti’s theorem. The theoretical rationality of the proposed method is analyzed, and the workflow is provided. The data and simulation models for a model test were adopted to validate the effectiveness and accuracy of the proposed method. The results show that the external loads can be back-analyzed with satisfying accuracy and low computational cost. Then, the practical application was conducted for an in-service shield tunnel. In addition, the workflow combined with laser scanning and back analysis was proposed for evaluating the practical loads. The proposed approach can be used for the back analysis of the external loads based on lining deformation scanned inside tunnels, with good performance.

In this paper, the dynamic response of underground rectangular fluid tank resting on an elastic foundation and subjected to arbitrary dynamic loads is developed in the form of analytical solution. The dynamic responses investigated are deflection, bending moment, and shear force of the tank. The underground rectangular tank is assumed to be a frame composed of horizontal and vertical beams resting on an elastic foundation. The mechanical resistance of elastic foundation is modeled using spring elements that account for soil resistance due to compressive strains in the soil. The fluid in the tank is assumed as inviscid and irrotational, and the influence of free-surface wave is ignored. An analytical solution of free vibration modes of empty tank (dry modes) is derived at first, and then the free vibration modes of fluid tank infilled with water (wet modes) can be obtained by the dry modes. Based on the wet modes, the explicit formulations of dynamic responses of the tank are finally obtained by the modal superposition method. The solutions for several cases, such as empty tank and fully filled fluid tank subjected to harmonic loads, are also discussed. Further parametric analysis is carried out to investigate the influence of the soil–structure relative stiffness ratio on dynamic responses of the fully filled fluid tank.

Disease in the liner back cavities of operational metro tunnels is alternately affected by groundwater environment, train cyclic load, and ambient environment conditions. Cavity disease is characterized by high levels of hiddenness and uncertainty; it also easily induces other tunnel diseases which can reduce the structure’s bearing capacity and degrade structural safety and stability throughout the tunnel. This paper proposes a novel cavity-locating method for operational shield tunnels, with special focus on single- and multiple-cavity diseases. Based on perturbation theory, dynamic behaviors (modal frequencies and shapes) of different cavity cases were obtained from an analytical model of the original tunnel structure. A modal strain energy cavity indicator (MSECI) was established to reveal the locations of both single cavity and multiple cavities. A typical shield tunnel was modeled as an Euler-Bernoulli beam on a Winkler foundation and evaluated to validate the proposed method. The perturbation theory appears to effectively characterize the dynamic characteristics of liner back cavities in metro tunnels. MSECI can be used to locate cavities accurately. This work may provide a valuable theoretical basis for the detection and analysis of tunnel cavity disease and other tunnel health-monitoring applications.

Train‐induced vibration is increasingly attracting people’s concern nowadays. In the coastal areas, many metro tunnels are built in the soft deposits, so the train‐induced vibration effect is more serious. Nevertheless, the existing research studies mainly focus on the dynamic responses in the tunnel or on the ground surface while vibration characteristics in the ground are seldom studied. In this paper, a comprehensive field measurement was performed by installing accelerometers in the tunnel and soil layers and on the ground surface to capture the response characteristics of the track‐tunnel‐ground system. Elastoplastic numerical simulation considering the soil‐water coupling was conducted to reveal the responses of acceleration, dynamic displacement, and excess pore water pressure using FE code DBLEAVES. Measurement results indicate that high‐frequency contents (>500 Hz) attenuate rapidly in the propagation process; the dominant frequency of the rail concentrates in the middle‐ and high‐frequency bands, about 25–400 Hz and 1000–1500 Hz, while the frequencies of the track bed, soil layers, and ground surface drop to below 400, 200, and 100 Hz, respectively. The vertical ground acceleration decreases like an arc in the transverse direction while there is transverse acceleration amplification phenomenon at a distance from the upper haunch and lower haunch of the tunnel. Overall, the area affected by train vibration in the soft deposits is about 30 m away from the metro tunnel. Numerical simulation based on soil‐water coupled analysis is feasible to model the vibration characteristics in the soft deposits and confirms that there is acceleration amplification in the ground. Moreover, numerical results indicate that excess pore water pressure can be accumulated during each train vibration, so the train‐induced settlement will be a potential problem in the long term for the metro tunnel.

The structural health of operational metro tunnels is closely related to public safety. Prior research has focused on the locations of structural damage, but few researchers have examined both the location of damage and identifying the degree of damage, especially in metro shield tunnels. This paper proposes a new method for identifying structural damage that entails locating and detecting the degradation of tunnel performance, with a special focus on characterizing the degree of damage. First, the dynamic behaviors (modal frequencies and shapes) of different damage levels are obtained from an analytical model of the original tunnel structure. Second, a modal strain energy damage indicator (MSEDI) is introduced to locate the damage, regardless of size. Once the location of the damage is identified using MSEDI, a fuzzy logic-based damage identification (FLBDI) method is used to determine the actual extent of the damage. Finally, a simplified model of the tunnel is created using the Euler-Bernoulli beam theory and Winkler’s foundation, to further test the procedure under an incomplete modal information condition and with differing noise levels. The results reveal that the fuzzy logic- based system can identify the degree of damage and structural degradation with very high accuracy, in which the location of damage and the prediction of performance degradation is satisfactorily confirmed.