Assessment of the barrier effect caused by underground constructions on porous aquifers with low hydraulic gradient: A case study of the metro construction in Barcelona, SpainReportar como inadecuado




Assessment of the barrier effect caused by underground constructions on porous aquifers with low hydraulic gradient: A case study of the metro construction in Barcelona, Spain - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

1 Amphos 21 2 Institute of Environmental Assessment and Water Research IDÆA, Barcelona 3 BRGM - Bureau de Recherches Géologiques et Minières

Abstract : Construction of tunnels can impact aquifers because of the changes produced in thenatural groundwater behavior. The drain effect, which is one of the most important impacts,can be eliminated using a tunnel-boring machine TBM to drill a tunnel with an imperviouslining. However, the use of impermeable linings results in aquifer obstruction, giving rise tothe barrier effect, which may cause an increase and decrease of the hydraulic head upgradientand downgradient of the tunnel, respectively. This modification of the hydraulic head, whichcan be predicted analytically and is proportional to the natural hydraulic gradient of theaquifer perpendicular to the tunnel N i before it is constructed, is negligible for aquiferswith values of N i that are very small or null approximately 0. In these cases, the analyticalsolutions are not useful to estimate the real impact because the head distribution is not largelyaffected.This study proposes a methodology to evaluate the hydrogeological impact producedby the construction of underground impervious structures in aquifers, which have a small ornull N i . The method, which is based on the analysis of the groundwater response to pumpingtests performed before and after construction, was tested in a stratified porous aquifer and wasused along with numerical modeling to assess the barrier effect in an experimental site SantCosme, El Prat de Llobregat, Barcelona. The impact on the head distribution was negligible.However, the reduction of the connectivity was considerable. Pumping tests can determine thechanges in aquifer connectivity caused by the construction of an underground imperviousstructure. The behavior of the groundwater during the post-tunneling pumping changes withregards to the pre-tunneling tests. A delay in the response to the pumping and a decrease ofthe drawdown are observed in the piezometers located on the opposite side of the tunnelwhere the well is placed, whereas an increase of drawdown occurs in the piezometers situatedon the same side of the well. The procedure explained in this paper reveals a useful tool fordetermining the impact caused by underground impermeable constructions in aquifers, whereN i is small or even 0.

Keywords : Tunnel porous aquifer Barrier effect Pumping Test TBM





Autor: Jordi Font-Capo - Estanislao Pujades - Enric Vàzquez-Suñé - Jesús Carrera - Violeta Velasco - Daniel Montfort -

Fuente: https://hal.archives-ouvertes.fr/



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