沉管隧道基础往往采用条带垄沟状先铺碎石垫层，该碎石垫层作为桩基与沉管结构传力构造的工程经验极少，为了解碎石垫层在工程荷载下的变形特性、传力机制及垄沟尺寸，及结构水平移动、回淤、垄沟偏位、桩顶倾斜等工程因素对其的影响等方面进行了物理模型试验研究。研究表明：（1）碎石级配的选择应同时考虑压缩模量、孔隙率、粒径等多种因素，过小粒径级配不适宜用于基础垫层；（2）垄沟的存在会大幅降低碎石垫层的压缩模量，压缩主要是由压密变形和垄沟导致的碎石颗粒侧向“挤出”造成；（3）支撑桩段碎石垫层的极限承载能力约为480 kPa，碎石垫层作为桩顶传力构造，受力变形机制复杂，个别影响因子十分敏感，需采取措施控制桩顶应力水平在碎石垫层极限承载能力范围内。

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