中文摘要：

舟山普陀区沈家门港海底隧道北岸明挖段基坑的南侧为浅海海域，海域内初步施工采用模袋砂围堰隔断海水。为了分析施工过程中围堰变形情况，对施工过程中围堰的沉降和水平位移进行监测，并与理论计算相对比。监测数据表明，在海底淤泥质土层上进行模袋砂围堰施工易受海水涨落潮时的水流冲刷、水位变化影响，围堰产生较大变形，最大沉降和水平位移量分别达74．1，216．6cm；用简化Bishop法计算的围堰稳定性也不满足要求。根据现场监测和理论计算将海域内部分围护更改为钢管桩加既有模袋砂的隔断形式，围护形式调整后，沉降和水平位移得到有效控制。分析结果可为沿海淤泥质土地质条件下深基坑采用模袋砂围堰施工和设计提供借鉴。

英文摘要：

The undersea tunnel of Zhoushan Putuo District Shenjiamen Harbor in north shore is constructed by the way of open excavation. Shenjiamen Harbor is located in shallow sea area. At the beginning of construction, sand soil cofferdam was used to cut off sea water. Monitoring data show that sand bag used in silt soil is susceptible to water erosion of sea water tidal fluctuation and water level change, which will cause large deformation. The maximum settlement and horizontal displacement are 74.1 cm and 216.6 cm, respectively. The safety factor of cofferdam calculated by Bishop method is not satisfied, adjustment of the cofferdam should be made based on field monitoring and calculation. However, when the steel pipe pile was introduced to the cofferdam, settlement and horizontal displacement are effectively controlled. The results provide a reference for the construction and design of geomembrane bag with sand soil cofferdam in deep foundation of undersea tunnel under conditions of coastal muddy land.