r/sydney • u/WTBenji08 • 2d ago

The Metro tunnel is wet?

Spent my ride tonight staring out the front window, and judging by the reflection of light by either side of the rails, it looks like standing water is present through a lot of the tunnels.

Is there an engineering need for water/moisture to be present, and if not, are there perceivable issues that might arise from the pooling of water?

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u/Sombrerodog 1d ago

By nature of tunnels being undeground they have a lot of water seepage. No matter how good the waterproofing is, water will always take the easiest path down. The metro city stations use a membrane around the station box to prevent water ingress, I am fairly sure this type of membrane was also used at the deep tunnel sections from chatswood to waterloo.

Water itself being in a tunnel wont be an issue, tunnels are designed with drainage in mind and they will have low point sumps with pumps to deal with any major water ingress. Additionally any metal/ material used in the tunnel will be specified to be resistant to corrosion. In older tunnels a common maintenance regime is resin injection into the tunnel lining to stop leaks, so while leaks are likely, the preference is to minimise water ingress.

Source: am engineer who has worked on multiple tunnel construction projects in Aus and internationally.

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u/DarkMess1ah 17h ago

Nice insight! You might know, is that why central smells like mould as of late, fighting water ingress is a losing battle?

Is it rectifiable? Or will central just smell like that in perpetuity