Abstract：Xiamen Xiang¢an subsea tunnel is the first subsea tunnel in China. The ground settlement became large when the CRD method was adopted on the right line in Wutong side. So it is determined to change the excavation method，i.e. the both-side drift method. Combined with the construction site and ground settlement，the CRD method is then adopted. The main purpose is to find the possible reasons that cause the large settlement. First，it is focused on the influence of the excavation，and it is seen that the displacement of the tunnel is the main reason that causes the ground settlement. Second，the decreases of the cohesion and friction of soils that are caused by continuous rainfall are contributed to the large settlement. Third，the ground surface of soils is changed into artificial landfill compared with the completed parts. At the same time，the controlling effects of ground settlement when the excavation way is changed to adopt the both-side drift method are obvious. The development of ground settlement with this method is different from that with CRD method，though the maximal settlement is all located at the top of the subsea tunnel. Finally，the difference between the two methods on the controlling effects of ground settlement and the regularity of the surface deformation are summarized. It can provide references to the construction of the project，and it can be adopted for similar projects.
