为了探索硬质地基上干坞坞口模袋砂围堰变形的空间效应及合理的平面布置方案，以广州洲头咀沉管隧道轴线干坞坞口模袋砂围堰工程为背景，借助数值手段建立围堰三维有限元模型，明确了干坞内降水工况下围堰空间条件下的水平向变形规律，并结合现场实测数据进行了验证，同时对多折角U形和两直角U形2种围堰平面布置方案进行了对比。结果表明： 1）降水工况下，模袋砂围堰纵向不同位置的水平向变形规律不同，将围堰变形视为平面应变问题存在缺陷； 2）围堰存在类似于基坑的空间效应，其本质源于围堰自身平面布置导致的系统刚度差异； 3）围堰顶部斜裂缝产生的原因是围堰角部与中部系统刚度不同，差异变形的存在导致了裂缝的发育； 4）多折角U形围堰布置方案优于两直角U形布置方案，前者对空间效应的利用更为充分。

The sandbag cofferdam at drydock entrance of Zhoutouzui Immersed Tunnel in hard soil foundation in Guangzhou is numerically simulated by 3D finite element model, so as to learn the horizontal deformation rules of sandbag cofferdam under dewatering condition in drydock. And then site monitoring data are collected and analyzed. Meanwhile, comparison between the layout scheme of sandbag cofferdam with multiple folded corners U shape and that of two rightangle corners U shape is made. The results show that: 1) The horizontal deformation rules of different points along axial line of sandbag cofferdam are different under dewatering condition. The view of regarding cofferdam deformation as plan strain is defective. 2) The rigidity different of the cofferdam system induced by plan layout will cause spatial effect. 3) The cracks on cofferdam top are induced by differential deformation which is caused by different rigidities of corners and middle part of cofferdam. 4) The layout scheme of sandbag cofferdam with multiple folded corners U shape is superior to that of two rightangle corners U shape.