Calculation of surface settlement caused by excavation of shield tunnels with small turning radius

The settlement deformation caused by the construction of shield tunnels with small turning radius curve is very complicated, but the corresponding analytical method of deformation prediction is still not clear. According to the results of the previous researches, the formation loss model for construction of shield tunnels with curved section is established. Based on the mirror image method and the Mindlin solution, the formula for calculating the surface settlement caused by the excavation of shield tunnels with curved section is derived and applied to the calculation of engineering examples. Finally, the surface deformation laws and influencing factors of construction of shield tunnels with curved section are analyzed. The results show that the model for formation loss of curved section is reasonable and the derived formula is applicable to practical projects. The longitudinal surface settlement varies greatly in the range of 3 times the diameter of the hole close to the cutter head, a slight bulge on the surface within 3 times the hole diameter in front of the cutter head, and the maximum settlement position is located at 3 ~ 4 times the hole diameter behind the cutter head. The surface transverse settlement groove is asymmetrically distributed, and the maximum settlement position is at the inner side of the bend, about 1 time the hole diameter from the center line of the cutter disc. The surface settlement caused by formation loss is mainly affected by the turning radius and the length of the shield and shell, and the displacement degree of the surface transverse settlement groove is mainly affected by the diameter of the cutter disc.