Numerical modeling of shallow tunnels in unconsolidated sandy soils using a hypo-plastic model

Correctly predicting the behavior of the ground during tunnel excavation compared to what will happen in reality is a very challenging matter, especially in urban tunnels. On the other hand, the faster this prediction is and without the need to spend more money, the more valuable it will be. In the present study, the goal is to investigate the effectiveness of a hypo-plastic model to predict the results of physical modeling in the laboratory. For this purpose, the behavior of the surrounding environment of a tunnel in sandy soil was simulated using a hypo-plastic behavioral model, and the resistance characteristics of the studied soil were validated based on the triaxial test results. At the same time as simulating the tunnel excavation process, the settlement of the ground surface and stress changes in the soil above the tunnel were measured for different values of soil densities and tunnel depths. The results of this research showed a good agreement with the results of physical and theoretical modeling. Based on the results of this research, the hypo-plastic model can predict the behavior of loose granular soils. Convergence of the tunnel leads to disturbance of the stress field around the tunnel, and due to the phenomenon of soil arching around the tunnel, the stress distribution deviates from the linear state. Under the same conditions, although the loosened zone above the tunnel expands with the increase of the tunnel depth, the settlement of the ground surface decreases.