What indication do you have that the construction time for tunnel 3 is due to corruption or even that it's taking longer than necessary? It seems like a very large engineering project; sometimes those take time.
It’s a big project, and it is tricky to patch it after release. The thing is supposed to last 300 years, and usually we use infrastructure well past it’s intended lifespan…
That one is ~2600 years old
Ask Europeans ? They're bangin'em out.
Construction on New York's Tunnel #3 began in 1970. It was 28 years before any part of it was operational. A second section came online 15 years later (2013). The final stage isn't expected to be completed until 2032, a full 62 years after construction began. I'm unaware of any comparable tunnel project which has progressed at this slow of a pace.
It's similar in scope to this recently-completed second phase of NYC Tunnel #3, albeit carrying sewage rather than fresh water: 25 km long, 7.2 m in diameter in London vs 29 km long, 4.9 m diameter in NYC. Flow volumes are likely similar (a sewage tunnel will rarely run full).
Planning started in 2001, with construction beginning in 2016. It opened in May 2025, at a cost of around £5bn: https://en.wikipedia.org/wiki/Thames_Tideway_Tunnel
However, this is only the second phase of the plan, with two more phases broken out into separate projects. I've no idea if those were supposed to be a part of the original 50 year timeline or not.
These two questions are casually put next to each other in the same sentence but they're incredibly different. Personally, I don't think that corruption is a significant factor in how long it took. The second question is way too leading/framed - "necessary" doesn't exist past the physical limits.
For example, would the same project have taken the same time in China? No. Does that mean it should've taken as long as it would've in China, as clearly it took longer "than necessary"? Not by definition.