Underground utility tunnel is a passage built underground to carry utility pipelines such as electricity, steam, water, and sewer pipelines. To ensure the quality and efficiency of the construction, circumferential joints are always installed between two adjacent tunnel segments to prevent damage caused by shrinkage and creep of mass concrete in construction, and uneven settlement during daily operation. However, the lack of verification and quantification of the seismic performance of utility tunnel and internal pipeline system considering the effects of joints remains a critical deficiency of the design of utility tunnels in seismic intensive regions. This study aims to investigate the response of long-extended underground utility tunnel and internal pipeline system subjected to non-uniform earthquake ground motions. The utility tunnel and internal pipeline system are modeled as a double-beam system on foundation using OpenSees software. Soil-structure interaction, joint connections and internal pipeline pedestals are modeled as springs with different mechanical properties. A typical response-spectrum compatible bedrock ground motion (including two directions) is collectively amplified into different intensity levels. One-dimensional dynamic site response analysis and wave passage effect are conducted before dynamic analyses of the utility tunnel and internal pipeline system. The numerical results indicate that the utility tunnel joints can help to mitigate the seismic damage of utility tunnel, while enlarge the seismic response of internal pipeline. For the case of 0.20 g intensity level, the axial force, shear force, and bending moment of the utility tunnel with joints are 41.15%, 54.92%, and 78.09% less than those without joints, respectively; the internal pipeline in utility tunnel with joints exhibits significant increases of 21.67%, 1667.24%, and 40.02% in axial force, shear force, and bending moment compared to those without joints. The increasing rates of utility tunnel and internal pipeline responses diminish as seismic intensity levels rise, indicating a progressive plastic deformation within the structures.

Past major seismic events have demonstrated the vulnerability of almost any type of structure to large tectonic deformations. The present work focuses on a particularly important challenge for countries of high seismicity, related to the design of shallow tunnels against seismic faulting. A shallow reinforced concrete (RC) tunnel with continuous lining is analysed, embedded in dense sand, subjected to a propagating reverse fault rupture. A detailed 2D finite element (FE) model of the soil-tunnel system is developed in ABAQUS. Two advanced soil constitutive models (Hypoplastic and Mohr-Coulomb Hardening-Softening) are employed, carefully calibrated against triaxial compression tests at various consolidation pressures. The RC tunnel lining is modelled with the Concrete Damaged Plasticity (CDP) model, which can realistically reproduce tensile and compressive damage. Before imposing the tectonic deformation, the initial stress state of the soil is simulated in a first step, followed by modelling the tunnel construction sequence in a simplified manner. The reverse tectonic dislocation is introduced in a third step, modelling fault rupture propagation through dense sand and its interaction with the RC tunnel. The focus is primarily on tunnel deformation and damage in function of the applied fault dislocation and the location of the tunnel relative to the outcropping fault rupture.

The dynamic response of ultra-shallow embedded tunnels, such as ground penetrating shield tunnels (GPSTs), is markedly different from that of conventional one. Since GPST is partially exposed above the ground surface and partially submerged, it is crucial to investigate its seismic response. This paper discusses the preliminary results of a series of large-scale 1g shaking table tests, conducted at Tongji University. A large-scale tunnel-soil model was developed to accurately reproduce the tunnel joints, the cross-sectional and longitudinal stiffness of the tunnel, and the key soil parameters of the prototype problem. The model tunnel has a total length of 7.7 m, with the embedded depth ranging from -0.5D to 0.5D, where D is the tunnel diameter, while negative values indicate that the tunnel crown is above the ground surface. The Shanghai artificial synthetic wave was applied as seismic excitation in the transverse direction. Two types of tunnels, standard lining and open-crown lining were tested. The study focuses on analyzing the acceleration response and the ovaling deformation of the tunnel, in order to elucidate the dynamic characteristics of GPST. The results reveal a strong effect of embedment depth on tunnel seismic response. The decrease of embedded depth leads to a significant increase of accelerations. The tunnel exhibits a "whiplash effect", leading to strong shaking of the above-ground lining. The ovaling deformation increases with embedded burial depth. Overall, the response of the underground lining (D >= 0) is governed by soil-structure interaction (SSI), whereas the above-ground structure (D < 0) exhibits a pronounced whiplash effect due to the absence of soil confinement. Such effects need to be properly considered in the seismic design of GPST.

The tunnel crossing soil-rock strata is a common scenario in engineering construction, and it is more vulnerable to earthquake impact than that in uniform ground conditions, while related studies on this topic are scarce. This paper investigates the seismic characteristics of a segmental tunnel crossing soil-rock interface by 1g shaking table test. Regarding the ground-tunnel relative stiffness as a dominant parameter, materials of model soil and model rock are selected. A refined model tunnel is designed to reproduce the segmental feature of the prototype tunnel. An artificial earthquake wave is input from the shaking table along the transverse direction. Seismic performances of the model tunnel, including the acceleration, sectional deformation and longitudinal joint extension, are analyzed to evaluate the soil-structure interaction (SSI). The discrepant seismic responses of the tunnel portions in the two different strata are revealed by the acceleration data. Due to the spatial variation caused by the soil-rock ground condition, significant joint extension near the interface and large sectional deformation at the soil deposit are observed, while deformations of the tunnel portion in rock are negligible. This work presents part of the test data, and it could be used to verify the numerical model, which is aimed at analyzing the seismic performance of the very same segmental tunnel in soil-rock strata.

Based on the different purposes and utilities, the tunnels are constructed of various shapes such as D-shape, Horse-shoe, and Circular. Most of the shapes of the tunnel are designed based on the overburden load in the static conditions, but their behaviour in seismic condition is very complex and not well explored yet. There are number of tunnel damages reported during the past seismic events worldwide. In this study tunnels of different shapes in the rock mass are analyzed using Finite Element Method for harmonic loadings of different frequencies. Effects of shapes are observed in terms of axial stress, shear stress and bending moment generated in the lining of each shape and critical locations are identified at which stress concentration takes place. The stresses induced in the lining are maximum when frequency of excitation is near to the fundamental frequency of the system. The most affected shape identified is D-shape in which stress concentration takes place at the corners in both static condition as well as in dynamic condition. However best shape identified is circular which is obvious but in most of the cases circular shape does not fulfil the purpose i.e. the movement of vehicles is difficult, so other shapes are compared with these results. It was found that the best shape other than circular is horse-shoe.

In the seismic design of box-shaped cut and cover tunnels, the effect of interaction between the box structure and the ground must be considered. The ratio of the average shear strain of the entire box γ s to that of the ground γ g (strain transfer ratio γ s / γ g) is one of the most important parameters in the seismic design of tunnels, considering that the shear deformation of the ground can significantly damage tunnels. However, this strain transfer ratio γ s / γ g varies significantly depending on the ratio of the shear stiffness of the box Gs to that of the ground Gg (shear stiffness ratio Gs / Gg). This study presents the results of the FE analysis under the condition that the box is in contact with the bearing stratum, which has not been reported before. Although the ground is assumed to be elastic, joint elements are used to compare the effect of the sliding behavior. The results showed that for Gs / Gg < 1, the contact between the box bottom and bearing stratum reduced the strain transfer ratio γ s / γ g, whereas the influence of sliding behavior was almost insignificant. When Gs / Gg > 1, the contact between the box bottom and bearing stratum increased γ s / γ , whereas the sliding behavior reduced γ s / γ g. These results provide important information for the physical model test results. Furthermore, the author's research group conducted model tests using aluminum rods, and the results will be compared to the results of future model tests.

Taiwan is located at the intersection of the Eurasia and Philippine plates, where earthquakes frequently occur. Maintenance of underground infrastructure, such as buried pipelines, is an important municipal issue in daily life. The Taipei Water Department plans to construct multiple large-diameter water mains using the shield tunneling method underneath floodplains or rivers to enhance the performance of water pipeline facilities. The plan involves laying underground pipes after completing the tunnel and filling the annular gap between the pipeline and the concrete segments with backfill, such as cementitious material or controlled low-strength material (CLSM), to secure the pipeline. U-shaped ductile cast iron pipes are used as the main type of pipeline. This study aims to recommend a quantity of poured cementitious material (full and half-filled) for this kind of pipeline facility and consider three different compressive strength levels (10, 40, and 140 kgf/cm²). Numerical analysis was conducted using ABAQUS to analyze the effects of different poured amounts and compressive strengths of cementitious materials on the U-shaped pipe joints under pseudo-static conditions. Comparisons of the variations in elongation and rotational angles have been made among the cases. The study reveals that ductile cast iron pipes exhibit larger rotational angles and elongations under full-filled conditions than under half-filled conditions. The compressive strength of the cementitious-filled material has a negligible impact on the rotational angles and elongations of the pipeline. The simulations show that half-filled cementing material with lower compressive strength can provide the required support to secure the pipeline, representing the most cost-effective plan. As a result, this study can serve as a valuable reference for future engineering design and planning, contributing to reducing pipeline disasters and enhancing economic benefits.

Seismic activity can compromise the stability of tunnels and tunnel intersections within fractured rock masses. Therefore, it is crucial to assess the impact of tunnel shape and rock joint characteristics on their behavior during seismic events. This study investigates the effects of different tunnel shapes on rock mass behavior during seismic excitation. The results indicate that block detachment predominantly occurs in the vicinity of the tunnel's crown region, particularly at the intersection of two tunnels. The larger tunnel, referred to as the main tunnel, undergoes minimal deformation, less than 0.3 meters, when subjected to seismic excitation with an amplitude of 0.36g. Conversely, the smaller access tunnel exhibits substantial block displacement, exceeding 5 meters, primarily near the intersection of the two tunnels. This behavior is attributed to intersecting rock joints near the tunnel intersection, coupled with favorable joint dip angles, which facilitate block detachment and sliding during seismic activity. The detachment of blocks results in the formation of sharp, cone-shaped failure wedges, indicating potential failures even in tunnels with a horseshoe-shaped cross-section. Square-shaped tunnels display significant joint yielding and detachment of larger blocks exceeding 25m³ in volume, while horseshoe-shaped tunnels yield smaller blocks with volumes less than 10m³ due to their geometry. Analysis of cyclic shear stress-strain loops reveals nonlinear rock behavior, with greater nonlinearity observed in areas experiencing higher shear strain. Regions distant from potential failure surfaces exhibit steeper loops, indicative of higher stiffness and lower damping, while regions near potential failure surfaces display flat loops, suggesting reduced stiffness and higher damping characteristics.

This study aims to collect existing seismic fragility models for bored tunnels and cut-and-cover tunnels, classify them based on the shape and depth of installation, and analyze the changes of fragility curves for each category. The analysis included the methods used to develop the fragility models, the techniques employed to model the tunnel using both empirical and numerical approaches, and the earthquake input motions and damage index criteria used to compute damage probabilities. Furthermore, representative fragility models for each category were proposed by weighting the categorized models. For bored tunnels installed in rock formations, they exhibited relatively lower fragility compared to cut-and-cover tunnels. Based on these preliminary research findings, it was observed that the probability of damage decreases with increasing burial depth.