Relationships between geological formations and groundwater chemistry and their effects on the concrete lining of tunnels (case study: Tabriz metro line 2)
2016
Mineralogical composition of geological formations has a great effect on the groundwater quality, as it may result in the generation of harmful chemicals in groundwater leading to deterioration of concrete lining of tunnels. The present study investigates the future problems of the corrosiveness of concrete due to groundwater chemistry along Tabriz metro line 2 (TML2) in Iran. Having a length of 22 km, this subway entirely passes in an underground route along a general W–E direction. According to the geological map of the area and field survey, east part of the tunnel is excavated within marl–shale deposits with gypsum, and anhydrite and coal belonging to upper red formation and Baghmisheh formation. These formations have the greatest impact on deterioration of groundwater quality, as the values of EC, TDS, SO ₄ ⁻² , and Cl⁻ significantly increased in TML2 at the east part. In this regard, EC, Cl⁻, and SO ₄ ⁻² increased roughly from 502 to 29,700 µs cm⁻¹, from 71 to 5753 ppm, and from 51 to 8309 ppm, respectively, while TDS increased to 26,200 ppm. Marls existing in the study area including yellow, green, and gray/black marls, have the potential of corrosion because of containing aggressive substances, such as sulfate, chloride, and a high percentage of organic matter. Thus, it can be concluded that the groundwater in the east part is highly aggressive, and deterioration of concrete lining of the tunnel is expected in the near future.
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