## 4 Simulation Analysis of the Spatial Reticulated Grid Structure Segmentation and Snatch Assembly  
### Determination of the Joint Position of the Spatial Reticulated Grid  
Combined with the underground excavation tunnel project between Hengli and Panyu Square Station of Guangzhou Metro Line 22, research on the subsection scheme of the spatial reticulated grid support structure is carried out. The tunnel passes through moderately weathered granite, the surrounding rock is grade IV, the bulk density is 25,000 N/m\({}^{3}\), the elastic modulus is 5 \(\times\) 10\({}^{3}\) MPa, Poisson's ratio is 0.2, the cohesion force is 400 kPa, and the internal friction angle is 35\({}^{\circ}\). The burial depth is 26.5 m, the excavation section span is 14.9 m, the height is 11.95 m, and the spray layer thickness is 0.35 m.  
The general finite element software ANSYS is used as the calculation tool to analyze the mechanical characteristics of the tunnel support structure by the load-structure method. According to the \"Code for Design of Railway Tunnel\" [33], the vertical and horizontal uniform force of the surrounding rock are calculated, and then the equivalent nodal force of each node is obtained, and the formation spring is used to simulate the interaction between the surrounding rock and the structure.  
The Link10 element and the Beam3 beam element are used to simulate the interaction between the surrounding rock and the structure, and the lining support structure. A gravity load (g = 9.8 m/s\({}^{2}\)) is added to the finite element model through the ANSYS program, the tunnel lining weight is 24,500 N/m\({}^{3}\), Poisson's ratio is 0.28, and the elastic resistance coefficient is 600 MPa/m.  
Figure 15 is the internal force distribution diagram of the simulated support structure. From the bending moment diagram, some positions with zero bending moment in the support plane can be obtained. According to this, the joint position of the prefabricated support structure can be preliminarily set at the zero moment.  
Combined with the on-site construction method and the load characteristics of the surrounding rock, and taking into account the weight of the components, construction convenience and other factors, the spatial reticulated grid segmentation is systematically analyzed. Each ring of the arch is divided into 10 segments, and the specific joint division is shown in Figure 16a. The height of the upper and lower benches is 7.3 m and 4.65 m, respectively, and the components are divided into five types. The upper bench includes A and B components, and the lower bench includes C, D, and E components. Figure 16b shows the circumferential and longitudinal joint connection types of the spatial reticulated grid. Circumferential joints are connected by the end-plates and high-strength bolts of two adjacent components, and two different U-shaped bolts are used for longitudinal  
Figure 15: Internal force diagram of primary support structure. (**a**) Bending moment diagram and (**b**) shear force diagram.  
connections to be placed in the reserved holes, respectively. These connection types are easy to install and operate, and reduce the welding workload to a certain extent.