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

Abstract

Construction of tunnels can impact aquifers because of the changes produced in the natural groundwater behavior. The drain effect, which is one of the most important impacts, can be eliminated using a tunnelboring machine (TBM) to drill a tunnel with an impervious lining. However, the use of impermeable linings results in aquifer obstruction, giving rise to the barrier effect, which may cause an increase and decrease of the hydraulic head upgradient and downgradient of the tunnel, respectively. This modification of the hydraulic head, which can be predicted analytically and is proportional to the natural hydraulic gradient of the aquifer perpendicular to the tunnel (i N ) (before it is constructed), is negligible for aquifers with values of i N that are very small or null (approximately 0). In these cases, the analytical solutions are not useful to estimate the real impact because the head distribution is not largely affected. This study proposes a methodology to evaluate the hydrogeological impact produced by the construction of underground impervious structures in aquifers, which have a small or null i N . The method, which is based on the analysis of the groundwater response to pumping tests performed before and after construction, was tested in a stratified porous aquifer and was used along with numerical modeling to assess the barrier effect in an experimental site (Sant Cosme, 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 the changes in aquifer connectivity caused by the construction of an underground impervious structure. The behavior of the groundwater during the post-tunneling pumping changes with regard to the pre-tunneling tests. A delay in the response to the pumping and a decrease of the drawdown are observed in the piezometers located on the opposite side of the tunnel where the well is placed, whereas an increase of drawdown occurs in the piezometers situated on the same side of the well. The procedure explained in this paper reveals a useful tool for determining the impact caused by underground impermeable constructions in aquifers, where i N is small or even 0.

Leveling vs. InSAR in urban underground construction monitoring: Pros and cons. Case of la sagrera railway station (Barcelona, Spain)

“…Note that the representativeness of the predictions performed using this numerical model are supported by other studies and projects developed regarding the construction of La Sagrera Railway Station (Pujades et al, 2012b;Font-Capo et al, 2015;Serrano-Juan et al, 2016;Culí et al, 2016).…”

“…Regarding the Pliocene materials, the value of K of the fine materials (marls) ranges from 0.001 to 0.01 m/ d, and the value of K of the sands ranges from 0.1 to 10 m/d. These values were derived from the numerous hydraulic tests performed in the city of Barcelona during recent underground construction projects (Pujades et al, 2012b;Font-Capo et al, 2015;Serrano-Juan et al, 2016;Culí et al, 2016). Specifically, in the study site, the pumping tests undertaken before the start of the construction projects showed that the minimum and maximum hydraulic conductivity is 0.001 m/d and 700 m/d, respectively.…”

“…Three main geological formations are included in the numerical model: the Barcelona Plain (study site), the Besòs delta river (North, East and South-East) and the emerged (and altered) granites from the Palaeozoic (West). The geometry of the layers of the different formations was defined using data from the boreholes campaigns undertaken before starting the construction and also from geological data bases whose information has been recovered in the numerous projects developed in this area (Vázquez-Suñè et al, 2011;Pujades et al, 2012aPujades et al, , 2012bFont-Capo et al, 2015;Serrano-Juan et al, 2015Culí et al, 2016).…”

Use of hydrogeophysical data to determine the role of faults in the geometry of the Barreiras Aquifer, Brazil

“…In tectonic-structural terms, such structures as grabens and horsts can influence the aquifer geometries by controlling the space for sedimentary deposition of further saturated bodies (Díaz et al 2014). In addition, faults and artificial structures also play important roles in permeability, acting either as a barrier slowing the flow of water or as conduits between aquifers (e.g., Pujades et al 2012, Font-Capo et al 2015. Although the relationship between faults and aquifer geometry has already been established for several areas, such as southern California, USA (Landon et al 2015) and southeastern Tunisia (Chihi et al 2015), more study cases are needed to fully understand the role of faults on aquifer properties.…”

Karst Development Mechanism and Characteristics Based on Comprehensive Exploration along Jinan Metro, China

“…During the metro construction in karst areas, caves that have developed or are developing are often encountered, which pose great difficulties in tunneling by shield machine. As most of the karst caves are in non-filled, semi-filled, or rich muddy water-filled, a number of hazards including sink holes, karst collapse, and water inrush can easily occur in metro tunnel projects when they pass through karst areas [17,18].…”