Assessment of groundwater ingress to a partially pressurized water-conveyance tunnel using a conduit-flow process model:
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PAPER
Assessment of groundwater ingress to a partially pressurized water-conveyance tunnel using a conduit-flow process model: a case study in Iran Hossein Gholizadeh 1
&
Ahmad Behrouj Peely 2 & Bryan W. Karney 3 & Ahmad Malekpour 4
Received: 15 November 2019 / Accepted: 10 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Construction of a conveyance tunnel through rock often induces the ingress of groundwater into the tunnel, a flow that changes both the hydrogeological regime of the tunnel and its environment. To explore this key interaction, a novel modeling approach using the conduit flow process (CFP) is developed that considers both the hydraulic head and the ingress of water from the rock matrix during excavation. The resulting flow values are predicted through an adapted MODFLOW numerical model into which the tunnel is introduced with the aid of the new CFP approach. The CFP approach can simulate both laminar and turbulent flow in the tunnel whether the flow is free surface or pressurized. Several simulations, including one for which the permeability of the tunnel perimeter is assumed to be identical to the hydraulic conductivity of the surrounding rock matrix, are then used to explore the sensitivity of the predicted head and flow conditions to the permeability of the tunnel perimeter. Comparisons of the numerical results with field data from the Kerman Water Conveyance Tunnel in Iran show that the proposed approach accurately predicts the spatial variation of both groundwater ingress and hydraulic head. Keywords Groundwater hydraulics . Numerical modeling . Conveyance tunnel . Conduit flow process (CFP) . Iran
Introduction An accurate estimate of the ingress of water into a conveyance tunnel is crucial if engineers are to manage the cost of the tunnel’s lining layer and the associated danger to human life (Brassington 1986). Past studies have used both analytical and numerical models to determine the volume of leaked water. One early estimate by Goodman et al. (1965) analytically predicted the groundwater inflow by assuming a radial flow and a homogeneous stratigraphic medium. Later, Anagnostou
* Hossein Gholizadeh [email protected] 1
Rayab Consulting Engineers, Nelson Mandela Highway, Farzan-e-Gharbi Street, PO Box 14155-3963, Tehran, Iran
2
Department of Earth Sciences, Shiraz University, Shiraz 7146713565, Iran
3
Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario M5S1A4, Canada
4
Innovative Hydraulic Group Inc., 89 Loire Valley Ave, Thornhill, Ontario L4J 8V7, Canada
(1995), Lei (1999), Cesano et al. (2000), Celestino et al. (2001), El Tani (2003), Kolymbas and Wagner (2007) and Maréchal et al. (2014) also analytically predicted the inflow rate; Farhadian and Nikvar-Hassani (2019) presented a range of analytical methods, considering both their application domain and their validation. However, in reality stratigraphic properties and hydraulic conductivity of the rock matrix are inevitably variable and most a
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