Well, the picture above is just artistic fantasy, but the UK-France Cross-Channel Tunnel is well below the sea-bed, in a pair of tunnels (one each way) bored through a fairly soft but very dry, clay-like rock called the Chalk Marl. I think they are lined with concrete segments.
There are a couple of cross-overs within its length to allow trains to use the other tunnel if necessary, and a third, smaller service-tunnel for maintenance and emergency use.
The railway joins London to both Paris and Brussels, with stations on the coasts.
Cars are taken through it on special wagons while their occupants travel in the passenger coaches. I am not sure how freight is carried, but I think it is in containers or in bulk-goods wagons, not on lorries.
I don't know if this tunnel will cross a river or part of the sea, but there is nothing unusual in an underground-railway tunnel doing that, other than this being being India's first. These started in the 19C in London and below the Severn Estuary in SW England; and later, other cities on rivers, such as New York and Moscow followed suit.
I assume from the news report that the Tunnel in India will similarly be well below the river-bed at roughly 30m below surface. (I don't know why journalists don't quote actual depths rather than similes).
That under the R. Severn carries a double-track main railway line rather than part of an urban underground-railway system.
The unusual features of the Channel Tunnel are its length (more than 35km) below the sea.
Eurostar goes thru specially built tunnels also trains for cars and lorries
SW-User
How long did it take to build, I find the facts about the Channe tunnel, interesting it took 186 years from the conception of the idea for it to be realised.. 😆😆😆 Here are some interesting time line about it
