Calculation Method for Determining the Wall Displacement and Primary Support Bearing Capacity of Tunnels

The primary support structure of a tunnel often needs various support methods, such as bolts, steel arch frames, and shotcrete. It is of great significance to quickly calculate the displacement of tunnel walls and the bearing capacity of primary supports for guiding construction and ensuring construction safety. In order to solve the above problems, this paper constructs a mechanical model of primary support and analyzes the displacement of a tunnel wall at different construction stages of primary support; based on the Mohr–Coulomb strength criterion, the displacement of the tunnel wall at different stages of the primary support is derived, and the calculation method and process for calculating the bearing capacity of the primary support are given. The accuracy of the proposed method is then verified by an example. Compared with previous methods, the method proposed in this paper considers the support effects of bolts, steel arches, and shotcrete separately and calculates the corresponding displacement of the tunnel wall, which is closer to the actual construction situation. In addition, the bearing capacity of the primary support can be calculated and analyzed. By comparing with the numerical simulation results, it has been proven that the proposed method has a relatively small calculation error. Compared with the numerical simulation results and previous analytical methods, the method proposed in this paper is simpler and faster in calculation; thus, it can quickly assist in the design of tunnel support structures.