# Large Deformation Settlement Series Solution and Numerical Simulation for Underpass Project Track
## 4 Numerical Calculation of Track Settlement Deformation Based on ABAQUS  
ABAQUS software was used to establish a 3D solid model with a scale of 1:1 for finite element calculation to analyze the effect of underpass jacking of the frame culverts on the roadbed and track settlement deformation. Considering the symmetry of the structure, to reduce the calculation volume of the model, the model was selected to calculate half of the structure. The model mainly contains a frame culvert, roadbed soil layer, and track structure, among which the track structure consists of three components: track, rail sleeper, and roadbed. The size and material properties of each component of the model are set and selected according to the construction design drawings and geological survey data. Considering the boundary effect, the plane size of the overall model is 80 \(\times\) 44 m, the height is 50 m from the roadbed surface to the bottom of the soil layer [4; 28], the top surface of the model is free, the surrounding boundary is a horizontal constraint, the bottom surface is a three-way constraint, the symmetry surface is a symmetry constraint. The frame culvert structure is simulated by solid units, and the bed adopts wedge-shaped units, with an approximate global size of 4 and several individual component units of 120; the track, rail sleeper, frame, and roadbed soil layer all adopt hexahedral units, with the approximate global size of 1, 0.5, 2, and 2, with the number of individual component units of 1440, 12, 2329 and 20,160 respectively. A schematic diagram of the model is shown in Figure 6.  
Since the actual engineering has considerable complexity, it is impossible to maintain complete consistency with the actual engineering when establishing the numerical model. Therefore, according to the focus of the study, the model was simplified under the premise of ensuring the accuracy of the calculation results and reducing the difficulty of the model calculation. The basic assumptions are as follows:  
Figure 5: Monitoring point plan layout. Figure 6: Schematic diagram of the model. (**a**) Overall. (**b**) part. 1. The layers are simplified to ideal, isotropic, uniform elastoplastic soils with a uniform horizontal distribution of each layer. 2. The frictional resistance in the model is uniformly distributed. 3. Only the self-weight stress is considered when calculating the initial stress of the soil body, and the structural stress of the soil body is not considered. 4. The effect of groundwater level change is not considered due to the deep water table. 5. The connection between the rail and the rail sleeper is equivalent to the spring connection. 6. The load of rolling stock is ignored. The process of frame culvert with soil jacking is mainly reflected in the excavation of soil and the contact analysis of the box culvert and soil in the numerical simulation. The friction coefficient is taken according to the site survey report, and the normal contact is \"hard contact\" [15]. Considering the convergence of the calculation, the model adopts activation of the box culvert at the corresponding position to simulate the jacking process, while the soil in contact with the outer surface of the box culvert applies a surface load to simulate the friction force generated by the box culvert jacking on the soil. The value of the friction coefficient, friction force calculation reference [29; 30], the friction coefficient in the finite element calculation are taken as 0.3, 0.5, and 0.7 at the top, side plate, and bottom plate of the box culvert, respectively, and the three normal forces on the soil body are the self-weight of the overlying soil body, the active earth pressure borne by both sides, and the self-weight of the overlying soil body plus the self-weight of the box culvert, respectively.