Filling old coal chute

[CWi]

I have an old coal vault with a chute leading up from the ceiling to the pavement outside. The original metal cover is in place, apparently with a metal plate underneath. I Assuming I can remove the cover and plate to enable me to do it, I'd like to fill the chute. Should I use reinforced concrete, or would reinforced sand and cement be sufficient, please? Thank you.

 

[conny]

I shouldn't think you would need reinforced concrete as it won't be supporting anything.
You could simply tip a load of broken bricks, stones, gravel, and whatever else took your fancy, to bulk out the void then top off with 4"-6" of concrete tamped down hard to prevent it sinking.
PS Concrete is simply sand and cement with smaller stones mixed in to make it bind together better than sand and cement, which is more likely to crumble over time. Small, 20mm, chippings will be fine for them.

 

[RandomGrinch]

If the coal chute opens up onto a public highway (pavement), it  may be necessary to contact your local authority.

Here's an example from Bath (brief guidance attached):

Although, it isn't clear whether approval would still be required, if the existing cover was retained.

If you live in a conservation area, modifying or removing the original metal cover may also be subject to other consents.