Comparative Analysis of In-Situ Stress Field Inversion Results of Two-Dimensional and Three-Dimensional Models of Tunnels in the Feasibility Stage

To further study the in-situ stress field inversion accuracy of 3D and 2D tunnel models in the feasibility stage, according to the geological data of a railway tunnel in western Sichuan, 3D and 2D geological models were established by Ansys software, which was divided into ten strata and 11 faults, and numerical simulation was carried out by the finite element software Flac3D. The results show that: (1) The root mean square error between the two-dimensional model results and the measured ground stress is smaller and closer to the estimated value. (2) The two-dimensional model has a small scale. As a result, the relationship between the fault layer and the structure in the modeling process relative to the spatial position is finer, which can be suitable for the study of in-situ stress on the tunnel axis, determining the range of high pressure in the tunnel, and laying a foundation for predicting the geological disasters that may occur in the tunnel. (3) The three-dimensional model has an extensive simulation range and is less affected by boundary effects, which can simulate the actual situation of the topography and geomorphology strata in the tunnel site area. Still, the spatial relationship between faults and strata is relatively rough. Therefore, it cannot truly reflect the changes in the in-situ stress of responsibilities and other structures. This will cause specific differences between the simulated and measured values, which can be used to study the in-situ stress field in the tunnel site area. Furthermore, it can be used to study the change law of the in-situ stress field in a large area, laying the foundation for tunnel line selection.