Analysis of ground surface settlement in a shallow tunnel using coupled Eulerian-Lagrangian technique

The influence of the excavation angle on controlling ground subsidence induced by shallow tunneling was investigated. Laboratory tests were conducted to evaluate the effect of the inclination of the excavation surface. The test results indicated that decreasing the excavation surface angle leads to more stable tunnel conditions. The coupled Eulerian-Lagrangian (CEL) technique was validated through experimental tests. The applicability of the CEL technique for modeling the failure and post-failure behavior of soil during tunnel excavation was verified. Large deformation finite element analyses using the CEL technique were conducted to investigate the behavior of excavation face stability and excavation-induced settlement under various conditions, including excavation angle (α), cover equivalent diameter ratio (C/D), and internal friction angles of soil (ϕ). The results showed that ground surface settlement can be reduced by increasing the cover-to-diameter ratio and internal friction angle, and by decreasing the excavation angle. Moreover, it was observed that when the excavation angle was less than the soil’s angle of repose, the soil remained stable, and no surface settlement occurred. This observation is critical as it suggests that maintaining the excavation angle below a certain threshold can effectively prevent subsidence, thus ensuring the structural integrity of both the tunnel and the surrounding ground. Therefore, the excavation surface angle not only influences the stability of the tunnel during construction but also plays a pivotal role in controlling ground surface settlement in shallow tunnels.