Restoring groundwater levels after tunneling: a numerical simulation approach to tunnel sealing decision-making

Golian, Mohsen; Abolghasemi, Mahdi; Hosseini, Amirhossein; Abbasi, Mehdi

Restoring groundwater levels after tunneling: a numerical simulation approach to tunnel sealing decision-making | Rétablir les niveaux de nappe après creusement d’un tunnel: une approche par simulation numérique pour la prise de décision concernant l’étanchéification du tunnel Recuperación de los niveles de agua subterránea después de la construcción de túneles: un método de simulación numérica para la toma de decisiones sobre la impermeabilización de túneles 隧道开挖后恢复地下水位:隧道封闭决策的数值模拟方法 عددی به منظور تصمیمگیری در خصوص آببند کردن تونل احیای سطح آب زیرزمینی پس از تونلسازی:روشی Restaurando os níveis de água subterrânea após o tunelamento: uma abordagem por simulação numérica para a tomada de decisão na vedação de túneis

2021

Golian, Mohsen | Abolghasemi, Mahdi | Hosseini, Amirhossein | Abbasi, Mehdi

Tunneling is often unpopular with local residents and environmentalists, and can cause aquifer damage. Tunnel sealing is sometimes used to avoid groundwater leakage into the tunnel, thereby mitigating the damage. Due to the high cost of sealing operations, a detailed hydrogeological investigation should be conducted as part of the tunneling project to determine the impact of sealing, and groundwater modeling is an accurate method that can aid decision-making. Groundwater-level drawdown induced by the construction of the Headrace water-conveyance tunnel in Sri Lanka dried up 456 wells. Due to resulting socio-environmental problems, tunnel sealing was decided as a remedy solution. However, due to the expectation of significant delays and high costs of sealing, and because the water pressure in the tunnel may prevent groundwater seepage into the tunnel during operation, there was another (counter) decision that the tunnel could remain unsealed. This paper describes groundwater modeling carried out using MODFLOW to determine which option—sealed or unsealed tunnel—is more effective in groundwater level recovery. The Horizontal Flow Barrier and River packages of MODFLOW were used to simulate sealed and unsealed tunnels, respectively. The simulation results showed that only through tunnel sealing can the groundwater level be raised to preexisting levels after 18 years throughout the study area. If the tunnel remains unsealed, about 1 million m³/year of water conveyed by the tunnel will seep into the aquifer, reducing the operational capacity of the tunnel as a transport scheme. In conclusion, partial tunnel sealing in high-impact sections is recommended.

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