Looks like Accelerated Bridge Construction gone wrong. That segment on the ground doesn't look long enough to span between the supports, so I'm guessing it was a large, prefab section being advanced on rollers to the support in the ravine.
I suspect it is progressive construction - drag out a beam, bolt it on, drag out another. For the size of the beams the number on site seems appropriate. I suspect the unbalanced condition wasn't calculated.
Two spans built and pinned together so that one span balances the other as it is cantilevered and pushed out into position?
It looks as if the connection failed and a complete span dropped.
-------------------- Ohm's law
Not just a good idea; It's the LAW!
Tragic for those involved, but there are good reasons why that gorge has not been bridged before. The remoteness probably means that skilled labor and professional supervision is scarce. It is in that part of India which is to the East of Bangladesh, far from major Indian cities by land connections. They call this the Northeast Frontier Railway zone.
Reuters is now reporting that at least 26 workers died.