## 4 Analysis of the Mechanical Properties of Steel Sheet Pile Cofferdam Construction
### Mechanical Properties of Steel Sheet Pile Cofferdam after Construction Completion  
(1) Vertical stress and settlement of steel cofferdam  
The vertical stress simulation results of the steel cofferdam at different positions after the completion of the tunnel's construction are shown in Figure 11a. It can be seen that after construction was complete, the vertical stress at the top of the cofferdam showed compressive stress; from the lakeside to the foundation pit side, the vertical stress first increased with depth, increased to a maximum value of 0.23 MPa at 0.26 m, gradually decreased and tended to stabilize (all less than 0.01 MPa) at 0.26 m to 12.84 m, and gradually increased to the maximum value (0.23 MPa) at 12.84 m to 13.00 m (near the foundation pit of the cofferdam). On the lakeside, the vertical stress of the steel sheet pile showed compressive stress, which first increased with depth, increased to the maximum value (1.42 MPa) at 15.57 m, and gradually decreased at 15.57 m to 23.00 m (at the bottom of the steel sheet pile). On the foundation pit side, the vertical stress of the steel sheet pile showed compressive stress, which first increased with depth, increased to the maximum value (1.28 MPa) at 12.54 m, and then gradually decreased from 12.54 m to 13.00 m (at the bottom of the steel sheet pile). After the construction was complete, the maximum vertical stress of the steel cofferdam was 1.42 MPa, and the steel sheet pile cofferdam did not form a penetrating compression failure zone. The simulation results of the steel cofferdam's settlement after the completion of tunnel construction are shown in Figure 11b. It can be seen that from the side of the foundation pit to the side of the adjacent lake, the settlement of the cofferdam first increased and then decreased, reaching a maximum value of 8.17 mm at a distance of 0.53 m from the foundation pit; the settlement distribution was basically consistent with the distribution characteristics of vertical stress. The vertical stress and settlement in the steel sheet pile cofferdam caused by the tunnel's construction was relatively small, indicating that the bagged soil, geotextile and backfill soil laid on the water-facing side during construction could effectively suppress the settlement of the top of the cofferdam. (2) Horizontal displacement of steel cofferdam  
The simulation results of the horizontal displacement of the steel cofferdam after the completion of the steel tunnel construction are shown in Figure 12. It can be seen that after the construction was complete, there was an obvious settlement on the side cofferdam of the foundation pit; as the distance from the foundation pit increased, the settlement gradually decreased, and the overall horizontal displacement of the cofferdam was small, indicating that the steel sheet pile and round steel tie rod could ensure the overall stiffness of the cofferdam and limit its horizontal displacement. According to the simulation results of the deformation (settlement and horizontal displacement) of the steel sheet pile cofferdam, the  
Figure 11: Distribution of vertical stresses and settlements after the completion of tunnel construction. (a) Vertical stress. (b) Settlement. steel cofferdam tilted to one side of the foundation pit as a whole, with a tilt angle of 3.37\({}^{\circ}\), and the disturbance of the tunnel's construction to the cofferdam was relatively small. (3) Axial force on tie rod in steel cofferdam  
The tie rods in the steel cofferdam were numbered according to the positive direction of the Y-axis, and the axial force of the tie rods numbered 2, 4, 6, 8, 10, 12, and 14 was extracted.