Abstract: Flatness, vibrodensification parameters, and the post-treatment quality of rock cushions are critical to the success of vibrodensification operations in immersed tunnels. The authors combine field testing and particle flow numerical simulations to investigate the vibrodensification performance of rock cushions, using the Shenzhen-Zhongshan Link immersed tunnel as a case study. The effects of vibro-densification duration, cushion thickness, and vibration frequency on the densification behavior are examined, and the underlying mechanisms are interpreted from a microscopic perspective based on strong contact force chains. The main findings are as follows: (1) Cushion thickness is the dominant factor influencing the vibration-induced settlement of the rock cushion, while vibration frequency influences settlement within an optimal frequency range. (2) For rock particle sizes of 0.15–0.30 m, a cushion thickness of 1.2 m and a vibration frequency of 20 Hz, a vibro-densification time of 45 s yields better performance than durations of 20 s or 30 s. (3) At a cushion thickness of 1.2 m and a vibrodensification time of 45 s, the optimal performance is achieved with a vibration frequency of 20 Hz, outperforming frequencies of 10 Hz and 30 Hz. (4) For improved vibro-densification, a cushion thickness greater than 1.2 m is recommended under a vibration frequency of 20 Hz and a vibro-densification time of 45 s.

Key words: rock cushion, immersed tunnel, vibrodensification test, particle flow simulation, static load test