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The areas where tunnels crossing faults are especially susceptible to seismic damage. Local site effects associated with fault site notably contribute to the unfavourable impact on the seismic behaviour of tunnels. In this study, large-scale shaking table tests were conducted to investigate the fault site effect and its impact on the seismic response of tunnels. Real earthquake records, synthetic seismic wave, and sinusoidal waves were selected as input motions, excited in both transverse and longitudinal directions of the tunnel. The local site effect of the fault site was evaluated by time-frequency analysis. The test results indicate that the acceleration response within the fault is significantly greater than those on both sides, regardless of excitation direction. Dynamic characteristics of different regions of the fault site exhibit distinct variations under different excitation directions, with the dynamic behaviour of the strata within the fault playing a crucial role. Marked waveform distortion and trapped waves can be observed within the fault, attributed to harmonic distortion, waveform conversion at fault interfaces, and varying seismic wave propagation pathways. The region of maximum seismic response of the fault-crossing tunnel predominantly occurs near the interface between the fault and the hanging wall. The seismic response of the tunnel located in the hanging wall exceeds that in the footwall. The dynamic characteristics of the fault-crossing tunnel are significantly affected by the dynamic characteristics of the strata around the tunnel, highlighting the necessity of comprehending strata dynamics in the seismic design of such tunnels. The aforementioned findings could offer valuable insights for the seismic design of mountain tunnels crossing fault zones. [ABSTRACT FROM AUTHOR]

The dislocation momentum is the design basis for anti-dislocation to tunnel when a tunnel crosses an active fault. The influence of different dislocation levels on tunnel performances is not clear. Thus, based on seismic activity parameters at the site of interest and probability of fault dislocation, probability fault displacement hazard analysis (PFDHA) methodology was introduced in this paper to ascertain the fault dislocation level under different exceeding probabilities (63%, 10%, and 2%–3%). Then, based on the definition of different ground motion strength and fortification goals of the tunnel, a three-level fortification goal with different performance requirements of the tunnel was proposed. The first attempt to use the proposed indexes including the maximum dislocation of the tunnel and maximum relative deformation of the tunnel was tried to evaluate deformation and failure states with an experimental approach. Subsequently, the feasibility of the three-level fortification goal was further investigated according to the self-defined qualitative description and quantitative indexes in the segmental design and sectional expansion tunnels comprehensively. The results show that the fault dislocations relying on PFDHA at the site of the Shantou Submarine Tunnel are firstly ascertained as 0.04, 1.8, and 2.4 m respectively. Taking the fault dislocation as model input values into account, the dislocation mechanism of the tunnel under the three levels was revealed. More importantly, judging from the dislocation performance requirements of the three-level fortification goal, the tunnel deformation and failure states are mitigated by adopting the countermeasures. The sectional expansion design can well meet the requirements without the restriction of a strong earthquake, while the effectiveness of the segmental tunnel can be proved under frequently occurred and fortification earthquake. The final research results are expected to provide a new fortification goal for anti-dislocation hazard evaluation on expansion design in high-intensity seismic regions and segmental design in slight and moderate-intensity seismic regions.

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Tunnels built in geologically active areas are prone to severe damage due to fault dislocation and subsequent earthquakes. Using the Ngong tunnel in the East African Rift Valley as an example, the dynamic response of a fault-crossing tunnel and the corresponding sensitivity are numerically simulated by considering four factors, i.e., tunnel joint stiffness, isolation layer elastic modulus, strike-slip fault creep-slip and earthquakes. The results show that a valley-shaped propagation of peak displacement at the tunnel invert occurs in the longitudinal axis direction under an earthquake alone. Then, it transforms into an S-shaped under strike-slip fault creep-slip and subsequent seismic shaking. The tunnel invert in the fault zone is susceptible to tensile and shear failures under strike-slip fault creep-slip movements of less than 15 cm and subsequent seismic shaking. Furthermore, the peak tensile and shear stress responses of the tunnel invert in the fault zone are more sensitive to fault creep-slip than earthquakes. They are also more sensitive to the isolation layer elastic modulus compared to the joint stiffness of a segmental tunnel with two segments. The stress responses can be effectively reduced when the isolation layer elastic modulus logarithmic ratio equals −4. Therefore, the isolation layer is more suitable to mitigate the potential failure under small strike-slip fault creep-slip and subsequent seismic shaking than segmental tunnels with two segments. The results of this study can provide some reference for the disaster mitigation of fault-crossing tunnels in terms of dynamic damage in active fault zones. [ABSTRACT FROM AUTHOR]

• The first recorded instance of damage to a high-speed railway tunnel crossing a seismogenic fault. • The seismic damage and mechanisms of fault-crossing and non-fault-crossing tunnels were emphasized. • The combined effects of transient displacement and release of strong seismic motions from seismogenic faults were emphasized. • Five-segment damage zoning method for fault-crossing tunnels after an earthquake. In regions with complex geological environments, tunnel projects are highly susceptible to severe damage during strong earthquakes, posing significant challenges for the construction and operation of essential lifeline projects. Therefore, it is crucial to understand the dynamic response of tunnels under strong earthquakes. This study focused on the severe damage caused to multiple highway and high-speed railway tunnels by the 2008 Wenchuan Mw7.9 earthquake and the 2022 Menyuan Mw6.7 earthquake. Based on the damage characteristics, the damage types of highway tunnels and high-speed railway tunnels were classified into five typical types: lining cracks, lining spalling and collapse, construction joint damage, pavement or bottom structure damage, and water leakage. By considering the characteristics of near-fault seismic motions, such as pulse, energy, and time–frequency, as well as fault properties and geological conditions, a comparative analysis and mechanism study were conducted to emphasize distinctions between fault-crossing and non-fault-crossing tunnels, as well as the influence of seismogenic faults on tunnel damage. The importance of the combined effects of transient displacement and the release of strong seismic motions from seismogenic faults on damage to fault-crossing tunnels was emphasized. Moreover, based on the relationship between the degree of damage and the distance from the fault zone in fault-crossing tunnels, a five-segment damage zoning method was proposed, including the fault-crossing section, near-fault section, fault-affected section, portal-affected section, and conventional section. Through this study of the actual seismic damage characteristics and mechanisms of tunnels, valuable insights are provided for improving the resilience of lifeline tunnel projects. [ABSTRACT FROM AUTHOR]

Tunnels built in geologically active areas are prone to severe damage due to fault dislocation and subsequent earthquakes. Using the Ngong tunnel in the East African Rift Valley as an example, the dynamic response of a fault-crossing tunnel and the corresponding sensitivity are numerically simulated by considering four factors, i.e., tunnel joint stiffness, isolation layer elastic modulus, strike-slip fault creep-slip and earthquakes. The results show that a valley-shaped propagation of peak displacement at the tunnel invert occurs in the longitudinal axis direction under an earthquake alone. Then, it transforms into an S-shaped under strike-slip fault creep-slip and subsequent seismic shaking. The tunnel invert in the fault zone is susceptible to tensile and shear failures under strike-slip fault creep-slip movements of less than 15 cm and subsequent seismic shaking. Furthermore, the peak tensile and shear stress responses of the tunnel invert in the fault zone are more sensitive to fault creep-slip than earthquakes. They are also more sensitive to the isolation layer elastic modulus compared to the joint stiffness of a segmental tunnel with two segments. The stress responses can be effectively reduced when the isolation layer elastic modulus logarithmic ratio equals −4. Therefore, the isolation layer is more suitable to mitigate the potential failure under small strike-slip fault creep-slip and subsequent seismic shaking than segmental tunnels with two segments. The results of this study can provide some reference for the disaster mitigation of fault-crossing tunnels in terms of dynamic damage in active fault zones.

Tunnels, as critical underground infrastructures, often intersect with faults. Field investigations have underscored the susceptibility of fault-crossing tunnels to extensive damages during earthquakes. Hence, large-scale shaking table tests are conducted to investigate the deformation pattern and failure mechanism of fault-crossing tunnels under transverse excitation, particularly in non-rupture scenarios. The dynamic behavior of the tunnel, as expected, is dominated by the surrounding strata. Acceleration responses vary notably across different regions of the fault site. The disparity increases with the increments of seismic intensity and input frequency. The tunnel section at the interface between the fault and the hanging wall manifest the strongest acceleration, where the largest strains of the tunnel and most of the lining cracks also occur, highlighting its vulnerability to seismic vibrations. The damage-induced non-linearity of the tunnel is then identified by the decreasing dominant frequency thereof. The fault-crossing tunnel exhibits unique three-dimensional shearing-torsional deformations, elucidated through the test data and an analytical model. This deformation pattern provides a better understanding of the seismic responses of fault-crossing tunnels under seismic vibrations. • Dynamic responses of fault-crossing tunnels under seismic vibrations are studied by large-scale shaking table tests. • Faults have significant influence on tunnels under seismic vibrations even without rupture. • Vulnerable region of the tunnel, which is most intensely affected by the fault, is identified. • Deformation pattern and failure mechanism of fault-crossing tunnels under seismic vibrations are revealed. [ABSTRACT FROM AUTHOR]

An individual fault dislocation or seismic effect is often considered to investigate the deformation and failure of a fault-crossing tunnel, while emerged in high-intensity seismic zones, it will be likely to subject to a superimposed effect from fault dislocation and strong seismic excitation. In this study, a three-dimension numerical model to simulate fault dislocation and subsequently dynamic response characteristics of fault-crossing tunnel was established, in which fault dislocation and earthquake levels at the site of interest. The nonlinear damage feature of tunnel was considered to furtherly reveal damage states of tunnel under the superimposed effect. And then, a quasi-static large-scale model test was performed to verify the correctness of pre-order fault dislocation calculation results. The results showed that only when the tunnel was subjected to fault dislocation, a prominent relative deformation of tunnel exists in the fault fracture zone and tension and compression zone were noticeably identified at the convex and concave zones respectively. After superimposing the seismic loading, acceleration and equivalence plastic strain amplification of tunnel near the fault fracture zone is great of significance and the damage of the tunnel under the fault dislocation was concentrated at the fault core. More importantly, the fault-crossing tunnel is more of sensitivity to the initial fault dislocation from the obvious rising on the tension damage index, and when PGA is greater than 0.2 g, the tunnel emerged in the host rock mass should also be paid more attentions, not only the tunnel in the potential fault-affected zone. [ABSTRACT FROM AUTHOR]

[Display omitted] • Large-scale shaking table model tests were performed on fault-crossing tunnels. • Discrepant responses along the longitudinal direction of the fault-crossing tunnels were quantified. • Aseismic effect of grouting on the fault-crossing tunnel was investigated clearly. • Optimized seismic design parameters for grouting were discussed. Tunnels crossing inactive faults may experience large differential deformations along their lengths during earthquakes, resulting in damage. Faults always have inferior material properties for historical geological reasons. Grouting is an auxiliary construction measure in fault-crossing tunnels and has the potential to be an economical and effective aseismic measure. However, the feasibility and seismic mitigation mechanisms of grouting in fault-crossing tunnels have not been sufficiently studied. In this study, large-scale shaking table tests were conducted to verify the aseismic effect of grouting in a tunnel crossing an inactive fault and to explore the seismic mitigation mechanism behind it. On this basis, verified numerical models were developed to determine the optimized design parameters. The test results indicate that grouting reduces the acceleration response of the tunnel within the fault and reduces the differences in the acceleration responses in the longitudinal direction of the tunnel induced by the fault. As grouting increases the shear strength and stiffness of the strata around the tunnel within the fault, the strain of the tunnel invert is effectively reduced by over 80%, and the potential damage of the invert uplift is reduced simultaneously. Meanwhile, grouting effectively reduces the diameter deformation of the tunnel within the fault and reduces the differences in tunnel deformation in different areas of the fault site. By reducing the resonance caused by the frequency components of the input seismic wave that is close to the natural frequency of the strata, which contributes most to the tunnel response, grouting effectively reduces the seismic responses of the fault-crossing tunnels. Increasing the stiffness of the grouting zone is an effective approach to improve its seismic mitigation performance. In the example of this study, adjusting the relative stiffness ratio to approximately 100 between the grouting zone and the fault resulted in a favorable condition for aseismic effects, which could be deemed to be a suitable parameter for grouting. The above results can provide a reference for the seismic design of mountain tunnels crossing inactive faults. [ABSTRACT FROM AUTHOR]

To mitigate the seismic damage of the fault-crossing tunnel, this paper researches the scope influenced by the fault and proposes a setting method of the segmental lining. It is concluded that the segmental lining has a significant effect on reducing the shear stresses and compressive stresses, and the shorter the segment, the more obvious the effect. Furthermore, the normalized parametric analyses show that the seismic damage degree of fault-crossing tunnel increases with the decrease of the value of D / t (D is the tunnel diameter and t is the wall thickness), and the arch springing with the smallest D / t is the most critical position to be damaged. The middle section of fault rupture zone is the most dangerous and the seismic effect of the tunnel structure on the hanging wall is more severe than the seismic effect on the footwall. The proposed influenced scope of tunnel structure and the setting method of the lining segment can provide a reference for the aseismic design of the fault-crossing tunnel. • The influenced scopes of fault-crossing tunnel with varying fault widths were determined. • The design concept of the segmental lining that used to counter the fault was proposed. • The seismic response of tunnel lining was researched based on non-dimensional groups. [ABSTRACT FROM AUTHOR]