Assessment of Near-Fault P-Wave Incidence Angle on Seismic Performance of Rock Tunnels

Due to the spatial relationship between fault zones and tunnels, as well as the energy-rich and concentrated characteristics of near fault ground motions (NFGMs), the safety of tunnel structures is significantly affected. Consequently, seismic response studies of near fault tunnels have attracted increasing attention. Most existing research focuses on tunnel responses under vertically incident NFGMs. However, seismic waves are likely to act on the tunnel structure in an oblique incidence manner for near fault tunnels, the influence of oblique incidence angles of NFGMs on tunnel seismic responses remains unclear. To address the issue, a three-dimensional finite element model considering tunnel-surrounding rock interaction is established in this study. Based on the viscoelastic artificial boundary theory, P-waves of NFGMs are converted into equivalent nodal forces for input. The effects of different P-wave incidence angles on tunnel seismic responses and damage patterns are investigated. The results indicate that velocity pulses substantially magnify axial responses – including strain, axial force, and bending moment, revealing the dominant role in near fault tunnel seismic behavior. With increasing incidence angle, the peak axial acceleration of the tunnel first rises and then falls, while the vertical response decreases almost linearly. Hoop strain responses reduce with incidence angle, whereas axial strain responses are markedly amplified, concentrating damage at the springing line. Both bending moment and axial force reach their maximum values at an incidence angle of 60°.