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
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
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DOI：
10.1016/j.enggeo.2015.07.006
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发表时间：
2015-09
影响因子：
7.4
通讯作者：
Jordi Font-Capó;E. Pujades;E. Vázquez-Suñé;J. Carrera;V. Velasco;Daniel Montfort
中科院分区：
文献类型：
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作者：
Jordi Font-Capó;E. Pujades;E. Vázquez-Suñé;J. Carrera;V. Velasco;Daniel Montfort
隧道施工会影响含水层，因为自然地下水行为会发生变化。排水效应是最重要的影响因素之一，采用隧道掘进机（TBM）开挖防渗衬砌隧道可以消除排水效应。然而，防渗衬砌的使用会导致含水层阻塞，从而产生屏障效应，这可能会导致隧道的水头梯度和下降梯度分别增加和减少。水头的这种变化可以通过分析预测，并与垂直于隧道的含水层自然水力梯度（iN）（在隧道建造之前）成比例，对于iN值非常小或为零（约为0）的含水层来说，这种变化可以忽略不计。在这些情况下，分析解决方案是没有用的估计真实的影响，因为水头分布并没有很大的影响，这项研究提出了一种方法来评估水文地质影响的地下防渗结构的建设，在含水层，这有一个小的或nulliN。该方法，这是基于分析的地下水响应抽水试验之前和之后进行的建设，进行了测试，在一个分层的多孔含水层，并被用于沿着与数值模拟，以评估在一个实验场地（桑特科斯姆，El普拉德Llobregat，巴塞罗那）的屏障效应。对头部分布的影响可忽略不计。然而，连接的减少是相当大的。抽水试验可以确定地下防渗结构的建造所引起的含水层连通性的变化。隧道开挖后抽水过程中地下水的行为相对于隧道开挖前的测试发生了变化。在响应的泵送和下降的下降的延迟被观察到在位于隧道的相对侧的压力计，其中放置的井，而下降的增加发生在位于同一侧的压力计的井。在本文中解释的程序揭示了一个有用的工具，用于确定所造成的影响，在含水层，其中，N是很小的，甚至为0的地下防渗建设。
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 tunnel-boring 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 (iN) (before it is constructed), is negligible for aquifers with values ofiNthat 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 nulliN. 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, whereiNis small or even 0.