A method to estimate concrete hydraulic conductivity of underground tunnel to assess lining degradation. (August 2015)

• Record Type: Journal Article
• Authors: Bagnoli, Paola; Bonfanti, Mirko; Della Vecchia, Gabriele; Lualdi, Maurizio; Sgambi, Luca
• Is Part Of: Tunnelling and underground space technology. Volume 50(2015)
• Page Start: 415
• Page End: 423
• Publication Date: 2015-08
• Subjects: Hydraulic conductivity -- Underground tunnel -- Groundwater -- Concrete degradation -- Seepage model; Tunneling -- Periodicals; Underground construction -- Periodicals; Tunnels -- Periodicals; Underground areas -- Periodicals; 624.193
• DOI: 10.1016/j.tust.2015.08.008
• Languages: English
• ISSNs: 0886-7798

Abstract

Graphical abstract: Highlights: Hydraulic conductivity as a proxy of concrete degradation in underground tunnels. NonDestructive method to estimate the hydraulic conductivity of the concrete lining. Ground penetrating radar to survey the degradation of tunnel lining thickness. Finite element model implemented to study the groundwater seepage in porous media. Total water inflow predicted as a function of the groundwater level variation. Abstract: The determination of the degradation state of underground concrete tunnels is a crucial issue for maintaining and monitoring the performance of these infrastructures. In particular, if the tunnel is totally or partially submerged, concrete deterioration and consequent changes in both lining thickness and hydraulic conductivity can have dramatic effects on the amount of water inflow, leading to an increase in maintenance costs as well as to possible interruption of the infrastructure serviceability. The hydraulic conductivity of the concrete lining is here proposed as a proxy of the overall degradation state of the structure, being this property directly correlated to porosity and to the presence of interconnected fissures and cracks. The aim of this study is to propose a simple and completely non-destructive method to estimate the hydraulic conductivity of tunnel lining concrete. Provided the availability of easy-to-collect in situ geometrical and hydrogeological data (i.e. tunnel geometry, water inflow, water table level), the method relies on a back analysis to estimate the hydraulic conductivity of the concrete, performed via the finite element method to solve the seepage equations in porous media. Ground Penetration Radar technique is coupled to the modelling approach to gain accurate data about the current lining thickness. The proposed method has been applied to the study of a real case of underground tunnel, used to prove the model reliability. Moreover, once estimated the hydraulic conductivity and thickness of the concrete, the model can be used to generate curves linking the total water inflow in the tunnel as a function of the groundwater level variations, allowing a real-time monitoring of the current hydraulic state of the infrastructure. This methodology, which can be considered of general validity and easy to be extended for the study of any underground tunnel, provides a simple and effective tool useful to prioritize maintenance works and to evaluate the consequences of different hydraulic scenarios.