Impact of silt content on the compression and settlement behavior of gravel cushions in immersed tunnel foundation

Siltation in the cushion layer is a critical issue influencing the foundation construction and the sinking of pipe sections in immersed tunnels. This study investigates the impact of silt content on the mechanical behavior of gravel cushions used in the Shenzhong Link immersed tunnel, combining laboratory confined compression tests and PFC3D numerical simulations. The macroscopic effects of varying silt proportions on displacement and settlement are analyzed, alongside the underlying microscopic mechanisms related to porosity, contact strength, and the formation of strong contact force chains. Results show that increased silt content leads to a reduction in both the void ratio and the contact elastic modulus of the gravel cushion, with a 10% increase in silt content causing a 13%-21% reduction in modulus. Additionally, higher silt content weakens the frictional and interlocking properties between particles, resulting in a significant increase in the number of strong contact force chains under high-stress conditions. This change facilitates more pronounced particle space recombination, further influencing the deformation characteristics of the gravel cushion layer.