Abstract: Gravel cushion is often used as the foundation of immerse tunnel; but the experience of using gravel cushion as the force transmission between pile and immersed tube tunnel structure has been lacking. Physical model tests have been carried out to reveal the deformation characteristics of gravel cushion and to examine the effects of ditch dimension, horizontal displacement of structure, sediment, ditch diverge, top incline and so on, upon the deformation characteristics of gravel cushion. The experimental results show that 1) small particle size gradation is not suitable for the foundation gravel cushion, and in selecting gravel gradation the compression modulus, porosity, particle size and other factors must be taken into account; 2) the existence of the groove can reduce compression modulus of gravel cushion greatly, and the main reason for this is that the joint effect of compaction and groove causes lateral extrusion of gravels; 3) at piled foundation sections, the ultimate bearing capacity of gravel cushion is about 480 kPa. As the force transmission structure between pile and immersed tube tunnel structure, the force mechanism of the gravel cushion is complicated, and several factors may come into play in influencing the behaviors of the gravel cushion. Hence, some measures need to be adopted to control the stress of the pile top within the ultimate bearing capacity of gravel cushion

Key words: immersed tube tunnel, foundation, gravel cushion, deformation