A horizontal non-homogeneous field adversely affects the seismic resistance of both the utility tunnel and its internal pipes, with seismic waves obliquely incident on the underground structure causing more significant damages. To address these issues, this study, based on a viscous-spring artificial boundary, derives and validates the equivalent junction force formula for the horizontal non-homogeneous field. It then establishes a three-dimensional finite element model of the utility tunnel, pipes, and surrounding soil to obtain the acceleration and strain responses of the utility tunnel and its internal pipes under seismic loading. Finally, it investigates the impact of different incidence angles of shear waves (SV waves) on the response of the utility tunnel and its internal pipes. It was found that as the PGA increases from 0.1 to 0.4 g, both peak acceleration and strain of the utility tunnel and its internal pipes increase. The peak acceleration of the utility tunnel and pipes initially decreases and then increases with the angle of incidence, while the strain increases with the angle of incidence, reaching its peak value when the angle of incidence is 30°. The acceleration and strain responses of the utility tunnel and pipe are higher in sand than in clay, with the peak acceleration strongly correlating with the angle of incidence of ground shaking. The findings of this study provide valuable insights into the seismic design of horizontal non-homogeneous field utility tunnel systems.

The traditional method of adding viscoelastic artificial boundaries and equivalent seismic loads has the disadvantages of a cumbersome adding process and a difficulty in finding errors. Therefore, this paper was based on the existing theory and derived the spatial oblique incidence equivalent node load method on this basis, integrating the ground stress equilibrium, dynamic stress equilibrium, and equivalent seismic load and boundary application into one plug-in. The oblique incidence of spatial SV waves was simulated using the finite element method, and its accuracy was validated through comparison with analytical results. Subsequently, the feasibility of the oblique incidence simulation method was further demonstrated through the use of pile foundation seismic subsidence response cases. Based on the three factors of seismic wave type, peak ground acceleration, and oblique incidence angle, the dynamic response of the helical piles was analyzed in depth, which confirmed that the effect of oblique incidence on the structure in the soil should not be neglected. This approach significantly reduces modeling time and establishes a solid foundation for analyzing the dynamic response of structures in geotechnical fields.