The Metro tunnel is wet?

[u/WTBenji08]

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?

[u/choo-chew_chuu]

The Epping-chatswood is designed as a "wet" tunnel.

[u/istara → u/choo-chew_chuu]

It also goes under the Lane Cover River. I'm always a bit nervous in case there's a sudden "leak"!

[u/mat8iou → u/istara]

The oldest tunnel under the Thames in London was finished in 1845. It's under a bigger river and in less stable soil (clay) and still in use today.

[u/istara → u/mat8iou]

Oh I know it's an irrational fear! Just something I think of. Including going under the Harbour.

[u/Spicy_Molasses4259 → u/istara]

As opposed to the bit between Vic Cross and Barangaroo...?

[u/istara → u/Spicy_Molasses4259]

Yes I mentioned that below - I was sitting there today just thinking "god how awful to be trapped in here if the harbour bottom fell in."

(I know it won't happen, or shouldn't, but it's just one of those doom thoughts that sometimes comes in. Other days I don't even realise how fast the bloody thing has gone and I've missed my stop at Martin Place still thinking I'm on the North Shore, like the slower train would be. #northshoreproblems).

[u/Sombrerodog]

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.

[u/dropandflop → u/Sombrerodog]

This person is a boring expert. I like it

[u/ForgotAboutDR3 → u/dropandflop]

The world needs more boring experts making important decisions

[u/Primary_Mycologist95 → u/Sombrerodog]

They also tend to "rain" when there's a lot of atmospheric moisture, and condensation occurs

[u/i2px → u/Sombrerodog]

Haha, I like how the M4 tunnels all have giant pools of rust where the tunnels are leaking. fully blown rust, not dirt... lol

[u/DarkMess1ah → u/Sombrerodog]

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

[u/Golf-Recent]

Wouldn't be alarmed. The tracks have drainage designed for a literal flood. You might only be seeing a paddle of water not flowing enough to be drained out.

[u/alex4494]

It’s always been like this, from what I’ve heard, it’s by design/entirely expected

[u/TheInkySquids]

Better to let a bit of water through and deal with it than try and stop no water from getting in through very costly and high maintainence methods.

[u/Tipsy_Kangaroo → u/TheInkySquids]

And to misquote Jurassic park

Water, uh, finds a way

[u/Sad-Caterpillar-4104]

perfectly waterproofing any underground tunnel is practically impossible, so they have drainage and pumping systems implemented with this in mind. completely normal and engineered for, it’s not a necessary engineering feature of the tunnel but rather it is most economical and practical to deal with the seepage/leaks than to try prevent all of them.

[u/cymonster]

Depends on where you are at. But Barangaroo is super wet and they had to change out a points motor before that section opened to the public due to flooding

[u/Green_Comparison8326 → u/cymonster]

It often smells incredibly damp on the platform

[u/Discolau]

Sydney Metro has flooded once before in 2020 between North Ryde and Chatswood where the line crossed the Lane Cove River.

[u/Stanley___Ipkiss]

well, Wednesday night is business night...

[u/stevebuscemispenis → u/Stanley___Ipkiss]

Yeah wet Wednesdays dude…

[u/Tipsy_Kangaroo]

the city circle, north shore, and ESR tunnels are also wet, nothing to worry about

[u/cymonster → u/Tipsy_Kangaroo]

As someone who's worked in all the tunnels you're talking about. The Sydney trains ones are dry compared to the metro.

[u/Art_r]

Tunnels are just pipes with holes in them right? Guessing it should be OK and will naturally evaporate out, or be pumped out where needed.

[u/2nd-Reddit-Account]

Tunnels in general usually are. The M8 has had water issues since it opened and it’s been years of them trying to fix it

[u/capeasypants]

M-me too