Abstract
The concrete lining in subway tunnels often undergoes cracking damage in coastal cities. The combination of cracked tunnel lining structures and high concentrations of corrosive ions in the groundwater (e.g., chlorine) can accelerate concrete erosion, reduce the mechanical performance of the lining structures and shorten the tunnel service life. This paper investigates the chloride ion concentration in the groundwater of several subway tunnels in the coastal city of Qingdao, China. Indoor experiments and numerical simulations are conducted to investigate the chloride ion transport behaviour and service performance of cracked concrete linings. The results are applied to predict the service life of lining structures. The crack depth in concrete linings is found to have the most significant effect on the transport rate of chloride ions, followed by the crack width. The numerical simulations are carried out using COMSOL software to study the chloride transport behaviour in cracked specimens and predict the service lifetimes of lining structures of different thicknesses, and the results correspond well with the experimental data. The durability of a concrete lining can be enhanced by increasing the thickness of the protective concrete layer. Additional measures are proposed for treating cracked concrete linings to resist chloride ion attack in subway tunnels.
Highlights
Lining cracks are a typical form of structural damage that can accelerate the chloride ion penetration rate and significantly reduce the service life of tunnel lining structures [13,14]
Indoor experiments were performed to investigate and analyse the chloride penetration of lining structures with various crack widths and depths, and numerical simulations were conducted to verify the accuracy of the experimental results
Several Qingdao subway tunnels were selected as the sample to analyse the chloride content in the groundwater
Summary
Ongoing urbanisation has increased the demand for subway tunnel construction worldwide, and numerous new tunnel systems have become operational in recent years. Lining cracks are a typical form of structural damage that can accelerate the chloride ion penetration rate and significantly reduce the service life of tunnel lining structures [13,14]. Audenaert et al [23,24] studied the effect of crack width and depth on chloride penetration using indoor experiments and numerical analysis and showed that notched specimens are more severely eroded by chloride than uncracked specimens and that the notch depth has a pronounced influence. Indoor experiments were performed to investigate and analyse the chloride penetration of lining structures with various crack widths and depths, and numerical simulations were conducted to verify the accuracy of the experimental results. The results are applied to predict the service life of concrete lining with different crack depths, and treatment measures are proposed to manage and maintain subway tunnels under corrosive environmental conditions
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