Effectiveness of Protective Strategies for Mitigating Deep Excavation Effects on Nearby Existing Tunnels

Deep excavations in an urban environment often pose significant challenges due to their close proximity to existing tunnels. This study evaluates the effectiveness of various passive interventions designed to mitigate the effects of deep excavations on adjacent tunnels. Seven commonly used protective strategies are investigated by employing mixed-in-place columns as passive earth reinforcement, jet-grouting (JG) columns as wall reinforcement or embedded barriers, JG slabs, and their respective combinations. Cement-based materials without reinforcement are modeled using an advanced Concrete model, which accounts for strain softening in tension and crack development. The Concrete model parameters are empirically estimated and then experimentally calibrated. The superiority of the Concrete model is highlighted in comparison with the Mohr–Coulomb model. The results show that, for the case study considered, the effectiveness index of using JG slabs is much higher than other passive interventions, followed by JG columns used as wall reinforcement or embedded barriers. The findings highlight the importance of targeting the underlying mechanisms, such as basal heave, to effectively control the effects of deep excavations on nearby existing tunnels.