Abstract
Analytical methods used in engineering practice for a preliminary tunneling design do not adequately account for the domain limitation due to a river. In order to forecast the flow rate that has to be extracted to reach a sustainable water head in tunnel, the design must consider the changes of river hydrometric level and their consequences on piezometric head. The river is taken in account and the constraints of analytical solutions are discussed assuming isotropic and infinite domain. In particular, the study develops a formulation considering the variation of hydrograph in the river and different location of tunnel in the aquifer nearby the stream. Then, this equation was applied to a preliminary tunneling design in Cannero Valley, Northern Italy (Piedmont). The results, compared with analytical model’s ones show that the analytical approach leads to a good estimation of the tunnel inflow and, the analytical to a preliminary evaluation of its most suitable location.
Highlights
Several mathematical relationships have been developed to describe the drainage effects of tunnels on rivers consisting of the withdrawal of river and massive inflow of large volumes of water in the tunnel
2004 have shown as a river presence can influence the tunneling inflow behavior depending on its nearby aquifer location, such as river distance and impermeable bedrock depth
The proper model for computation must take in account both river oscillations (Pinder et al, 1969) and bedrock depth respect to the tunnel base (Goode et al, 1987), in addition to the tunnel and aquifer properties
Summary
Several mathematical relationships have been developed to describe the drainage effects of tunnels on rivers consisting of the withdrawal of river and massive inflow of large volumes of water in the tunnel. For this reason heavy changes of piezometric head can occur opening a tunnel in saturated aquifer. Usual mathematical solutions are not suitable for practical cases least of all when occur complex geological settings It is analyzed the suitability of a solving technique that can allow to predict tunneling extraction flow nearby river even if it is a first approximation. The tunnel is located nearby Verbano Lake (Maggiore Lake) and crossed by Cannero River (Piedmont District, Northern Italy), affected by sudden floods that can propagate about some meters remarkable fluctuation to groundwater
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