Is it a bridge, or a tunnel, or just.....

....a concrete box?
Actually it is, I suppose, all three!
The story is that the rail line is being electrified and the existing tunnel under the F&C canal was too low for the overhead wires. So the contractors have simply dug the roof off the tunnel! The canal has been stoppered up with a coffer dam at each side and a couple of big pumps taking care of any leakage. The concrete box has enough headroom for the new wires and will support the rebuilt canal in due course. At least that is how it looks at the moment. Sounds easy but they have been working at this for months now so it might be more complex than that.
Who would be an engineer?!