Yongjiang immersed tunnel

built in 1987 and opened in 1995

is a 420 m long road immersed tunnel. It is on the soft soil foundation in a bend of Yongjiang River

which has caused large settlement. Moreover

the severe sediment deposition and 2.67m tidal range in Yongjiang River also have a great influence on the settlement of tunnel. Based on the monitoring data of settlement

the paper analyses the subsoil conditions

tide and desilting’s influence on settlement. And a finite element method based on fluid-solid coupling method is put forward to simulate the long term settlement

and the simulation results are in good agreement with the monitoring data. In addition

the key influencing factors of tunnel settlement

including subsoil condition

trench siltation and siltation and desilting above the element

are calculated and compared. The monitoring data and finite element analysis show that the subsoil condition is the main factor that determines the magnitude of settlement

and the settlement of tunnel on soft soil is much larger than that on other kind of foundations; because of the tidal range

tunnel is subject to an oscillation of elevation which may account for 4%~10% of settlement of operation period; the effect of silting on tunnel is obvious

but regular desilting can only decrease the settlement temporarily and cause the settlement cyclic variation. Although the monitoring data were obtained from a specific project

the conclusions of the study are sufficiently general and may apply in other immersed tunneling projects.