为有效控制上软下硬地质条件下海域围堰围护结构的变形，以汕头苏埃通道工程始发井及后配套基坑为依托，对基坑施工中围护结构水平位移、混凝土支撑轴力、地面沉降等项目进行全过程监测，分析围护体系的变形受力与开挖工序的对应关系。主要研究与结论如下： 1）围护结构的最大水平位移的发生位置随基坑开挖深度增加逐渐下移，围护结构水平位移与支撑轴力最大值都位于基坑中下部位置，且二者都表现了基坑西侧大于基坑东侧； 2）基坑周边未加固段地表持续沉降，加固段的地表沉降较小； 3）建立综合监测预警机制，对基坑施工薄弱部位提出预警，信息化指导施工，保证了基坑的施工安全，为后续类似地质条件下基坑支撑体系提出了优化建议。

The deformation of cofferdam structure in uppersoft and lowerhard formation in sea area is a serious problem and should be effectively controlled. The horizontal displacement of retaining structure, support axial force of concrete and surface settelement during foundation pit construction of Su′ai Tunnel in Shantou are monitored, and the relationship between the deformation mechanism of retaining system and foundation pit excavation process is analyzed. Main studies and conclusions are as follows: (1) The occurrence location of the maximum horizontal displacement of the retaining structure is gradually lowered with the increase of the excavation depth of foundation pit; the maximum horizontal displacement of the retaining structure and the support axial force are located in the lower part of foundation pit, which are larger at the west side than east side. (2) The unreinforced section around the foundation pit settles continuously, and the settlement of reinforced section is small. (3) The establishment of comprehensive monitoring and early warning mechanism can guarantee the construction safety of the foundation pit; and some optimization advices for foundation pit support system of similar projects in the future are proposed.