With the accelerated development of urban underground infrastructure, utility tunnels have become a critical component of lifeline systems. Ensuring their seismic resilience is essential, particularly in near-fault zones where ground motions often exhibit distinct velocity pulse characteristics. These pulses, characterized by short durations and high amplitudes, can drastically alter the seismic response of buried structures. However, systematic experimental research on how these velocity pulses affect the seismic behavior of shallow-buried, highstiffness utility tunnels is still scarce. This study addresses this gap by conducting a series of shaking table tests with longitudinal input motions to investigate the dynamic responses of a utility tunnel-soil system under velocity pulse-type and non-pulse-type ground motions.

The experiments were carried out on a shaking table array consisting of nine sub-tables. A 1/30 scaled model of the utility tunnel, made of organic glass due to its favorable mechanical similarity to the prototype, was carefully embedded within model clay soil. Actual near-fault ground motion records with velocity pulses and synthetic non-pulse ground motions whose response spectra are matched to relevant standards were employed as inputs. The peak ground acceleration （PGA） was scaled to three levels: 0.10g, 0.20g, and 0.30g. Accelerometers and laser displacement sensors were installed at various depths and structural levels to capture dynamic responses including acceleration, displacement, and frequency content.

The main findings are summarized as follows: ① Velocity pulse motions significantly amplified the seismic responses of the soil, particularly near the surface. These included greater peak accelerations and displacements compared to non-pulse velocity inputs. As the input intensity increased, the predominant frequency of the soil decreased, indicating stiffness degradation and energy redistribution caused by pulse effects. ② The structural response of the utility tunnel was also strongly affected by pulse characteristics. Acceleration amplification factors increased markedly at the upper levels of the structure under pulse-type ground motions, revealing enhanced vertical energy transmission. ③ The soil and structure exhibited synchronized dynamic behavior, particularly in terms of predominant frequency and spectral shape. However, the upper structural levels, due to reduced confinement, displayed more pronounced responses, indicating the emergence of free-vibration characteristics and reduced soil-structure constraint.

This study systematically examines the amplification mechanism induced by near-fault velocity pulse ground motions on utility tunnels. It reveals the interplay between input motion characteristics, structural geometry, and soil-structure interaction under strong ground motion scenarios. The results provide valuable experimental evidence.