Seismic response of utility tunnel systems embedded in a horizontal heterogeneous domain subjected to oblique incident SV-wave

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.