## 4 Results and Discussion
### Internal Force of Immersed Tunnel
#### 4.3.2 Shearing Force of Immersed Segments  
The shearing force of the immersed tunnel is mainly borne by the shear key, which is the main bearing structure to ensure the force and safety of the tunnel. Shear keys, especially the endpoint position and connection position of shear keys, are the key observation positions during the force analysis of a tunnel [43]. The eight shear keys of the S2-S3 segment joint are labeled A-H, as shown in Figure 20.  
The shearing force (absolute value) at the root of shear key in the numerical model was extracted for analysis, and the calculation results are depicted in Figure 21. The shearing force of shear key is approximately symmetrical, which is related to the fact that the whole immersed tunnel is a symmetrical structure. When the SV wave turns obliquely incident, the symmetrical tunnel shear key is subjected to asymmetrical force, especially the side of the side wall where shear key B is located as the wave front of oblique incidence, making the vertical shear value of shear key B significantly larger than other shear keys. The peak value of vertical shearing force appears at shear key B on the side wall, up to 1.338 \(\times\) 10\({}^{6}\) N. The vertical shearing force in the segment joint is mainly borne by the vertical shear key, and the vertical shearing force borne by the horizontal shear key is very small. The vertical shear key bears about 85% of the vertical shearing force, while the horizontal shear key only bears 15% of the vertical shearing force. This is because the horizontal shear key is connected with the outer surface of immersed tunnel, i.e., the horizontal shear key directly contacts the surrounding soil. When the segment is subjected to vertical force, the partial stress of horizontal shear key is released with the extrusion deformation of shear key on the surrounding soil. The peak value of transverse shearing force of the shear key is 2.873 \(\times\) 10\({}^{6}\) N, which appears at floor shear key E at an incident angle of 15\({}^{\circ}\). Most of the transverse shearing force in segment joint is borne by the horizontal shear key, while the vertical shear key hardly bears the transverse shearing force, especially the middle wall shear key, which directly penetrates the lining; therefore, the transverse shearing force borne by it is the smallest. The ratio of the horizontal shear key and vertical shear key to bear the transverse shearing force is about 9:1, and the middle wall shear key bears only 2% of the transverse shearing force. The distribution of the shearing force is closely related to the layout direction of shear key in the joint. The layout direction of the shear key in the joint determines the distribution of shearing force at the root of shear key. Both the transverse peak shearing force and the vertical peak shearing force of shear keys occur when the SV wave has oblique incidence. In consequence, each shear key only needs to be  
Figure 20: Distribution of shear keys at segment joint.  
checked for the shear capacity of the shear key direction, and the impact of incident angle should be considered.