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Active faults pose significant threats to the structural integrity of mountain tunnels in seismic active zones. Post-earthquake reconnaissance revealed that numerous tunnels were damaged during past earthquakes, specifically those crossing active fault zones. In this study, the structural response and damage mechanism of a water conveyance tunnel subjected to reverse faulting was investigated. A three-dimensional finite element model incorporating the cohesive interface elements was developed to simulate the nonlinear process of the reverse fault rupture. The ground deformation and tunnel damage characteristics predicted by the numerical analysis were in good agreement with the field observations and experimental results, which proved the feasibility of the proposed simulation scheme. Moreover, a parametric study was conducted to estimate the effects of dip angle, surrounding rock property, tunnel rigidity, and friction coefficient between linings on tunnel performance. The results showed that the damage zone with softer rock masses of grade IV to V, based on the Chinese Guidelines for Design of Highway Tunnel, generally led to moderate structural damage to the tunnel. The tunnel's performance in the damage zone can be further enhanced by increasing tunnel rigidity and smoothness of the external surface of the secondary lining. [ABSTRACT FROM AUTHOR]

In addition to seismic waves, coseismic displacement is also generated during earthquake events, which decreases gradually away from the seismogenic fault and may bring damages to tunnels in the area. This study aims to investigate the nonlinear response of tunnels under coseismic displacement induced by strike-slip fault. First, a method for applying coseismic displacement on the finite-element model (FEM) is developed by converting the displacement into equivalent nodal forces applied on the element nodes. Then, the nonlinear response of the tunnel under coseismic displacement is numerically investigated, considering the influence of the angle of the tunnel axis with respect to the fault trace, the epicentral distance, and the earthquake magnitude. The numerical results show that the tunnel might suffers tensile damages under coseismic displacement induced by the strike-slip fault, which indicates the coseismic displacement, as one kind of earthquake loads, should also be considered in seismic analysis for tunnels. Moreover, some other conclusions can be drawn: (1) The tensile deformation of the tunnel increases first and then decreases, as the tunnel axis changes from being perpendicular to the fault trace to being parallel to the fault trace, which is converse for the shear deformation; (2) the damage degree on the tunnel lining increases first and then decreases while the epicentral distance increases; (3) with an increasing earthquake magnitude, the tunnel damage increases dramatically. This study offers an insight into further research on tunnel response under coseismic displacement. [ABSTRACT FROM AUTHOR]

An analytical solution for the seismic-induced thrust and moment of the circular tunnel in half-space under obliquely incident P waves is developed in this study, which is the superposition of the solution for deep tunnels under incident and reflected P waves and the reflected SV waves. To consider tangential contact stiffness at the ground-tunnel interface, a spring-type stiffness coefficient is introduced into the force-displacement relationship. Moreover, the tunnel lining is treated as the thick-wall cylinder, providing more precise forecasts than beam or shell models used in previous analytical solution, especially for tunnels with thick lining. The reliability of the proposed analytical solution is assessed by comparing with the dynamic numerical results. Based on the proposed analytical solution, parametrical studies are conducted to investigate the effect of some critical factors on the tunnel's seismic response, including the incident angles, the tangential contact stiffness at the ground-tunnel interface, and the relative stiffness between the ground and the tunnel. The results demonstrate that the proposed analytical solution performs well and can be adopted to predict the internal forces of circular tunnels under obliquely incident P waves in seismic design. [ABSTRACT FROM AUTHOR]

Analytical solutions can quickly and simply evaluate stresses and displacements in tunnels and are widely adopted in the preliminary design phase of tunnels. Tunnels must be able to withstand static loading and seismic loading. This paper proposes new analytical solutions for the stresses and displacements of tunnels under static and seismic loading. The tunnel lining is treated as a thick-walled cylinder. Moreover, the contact stiffness coefficient k 0 and the stress release coefficient η 0 are introduced to consider the arbitrary contact conditions at the ground–lining interface and the amount of excavation unloading. The new analytical solutions are verified by comparison with finite element analysis results. The results demonstrate the accuracy and applicability of the proposed analytical solutions. In addition, parametric analyses are conducted to explore the effects of the stress release coefficient η 0 and stiffness coefficient k 0 at the ground–lining interface, as well as the incident angle α of shear waves. The analysis results indicate that the proposed analytical solutions offer satisfactory performance and can be applied as an effective tool for preliminary tunnel design. [ABSTRACT FROM AUTHOR]

Simplified analytical solutions are very useful tools for the seismic preliminary design of tunnels and can quickly and easily give seismic responses to structures. This study presents simplified analytical solutions for the stress and deformation of circular composite-lined tunnels subjected to in-plane S-waves. Unlike previous solutions for single-lined tunnels, the proposed analytical solutions are suitable for tunnels with arbitrary numbers of linings. Moreover, tunnel linings are treated as multilayer thick-walled cylinders in the new solutions. Compared with thin shell or beam models used in previous analytical solutions, thick-walled cylinders provide more precise forecasts. In addition, the slippage effect at the lining-lining and ground-lining interface is considered by introducing a spring-type flexibility coefficient into the interaction force–displacement relationship. To verify the proposed analytical solutions, dynamic numerical examples are studied. The proposed solutions have good agreement with the dynamic numerical results and outperform previous analytical solutions. Finally, parameter studies are conducted to investigate the effect of the flexibility coefficient, degraded zone around the outermost lining and steel plate supporting the innermost lining on the seismically induced stresses and deformations. The proposed analytical solutions are applicable for approximately evaluating the seismic responses of circular tunnels with composite linings. [ABSTRACT FROM AUTHOR]

A simplified analytical solution is developed for estimating the thrusts and bending moments of the circular tunnel in half space under the obliquely incident SV wave. The seismic waves impinging on the tunnel is obtained according to the elastic wave motion theory in half space firstly, which is the superposition of the incident and reflected SV waves and reflected P wave. Then, by considering the tunnel lining as a thick-wall cylinder, analytical solutions for internal forces of circular tunnel due to the incident and reflected SV waves and the reflected P wave are deduced, which enables more precise forecasts than previous analytical solutions by the thin shell model. The total tunnel internal forces are obtained finally through the superposition of the above solutions under three kinds of waves. The accuracy of the proposed analytical solution is verified by comparing with the dynamic numerical results. Moreover, the discussion about the effect of critical factors on the accuracy of the proposed analytical solutions is conducted, including the tunnel structure inertia, the seismic wavelength, the lining thickness and the tunnel depth. These results demonstrate that the proposed analytical solution performs well and can be adopted to predict the internal forces of circular tunnel under obliquely incident SV wave in seismic design. • Analytical solutions for circular tunnel in full space under SV and P waves are developed. • Analytical solution for circular tunnel in half space under obliquely incident SV wave is developed. • The present solutions are verified by comparing with dynamic numerical results. • Discussion about the effect of critical factors on the accuracy of the proposed analytical solutions is conducted. [ABSTRACT FROM AUTHOR]

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]

A circular tunnel in a homogeneous infinite ground subjected to a vertically incident shear wave with an arbitrary vibration direction in the horizontal plane is considered in this study. A simplified analytical solution with explicit formulations for the deformation and stress of the tunnel lining is presented here. The superposition of two solutions under SH and SV waves are derived first. In the analytical solutions, the tunnel lining is taken as a thick-walled cylinder, which enables more precise forecasts and is much closer to practical engineering than the thin shell model adopted in other previous solutions. Moreover, the analytical solutions consider the slippage effect at the ground-lining interface by introducing a spring-type flexibility coefficient into the interaction force-displacement relationship. The results of the analytical solutions are verified by a comparison with the results of the dynamic numerical solutions via a 3-D ground-lining interaction model under earthquakes; the results show good agreement. By using the analytical solutions, the effects of the vibration direction, ground condition, lining thickness and flexibility coefficient on the seismic response of the tunnel are investigated. Additionally, the appropriate range of seismic wavelengths for the analytical solutions is discussed. The proposed solutions can be applied to the seismic analysis and design of tunnel structures. • Analytical solution is presented for circular tunnel under vertically incident shear wave with arbitrary vibration direction. • The tunnel lining is treated as a thick-wall cylinder, which enable precise forecasts. • Different slippage effects at the ground-lining interface are considered. • Effects of vibration direction, ground condition, lining thickness and flexibility coefficient are investigated. [ABSTRACT FROM AUTHOR]