Replacing solid floor under a staircase

[TimM]

Hi - my first post on the forum, be kind please!

I'm excavating the floor in my hall, to replace it with an insulated concrete floor. The existing floor comprised
a thin screed sitting on
quarry tiles sitting on
a few inches of loose dirt and hardcore sitting on
clay.

The problem we're going to encounter is that the two supporting newels of the staircase simply rest on top of the quarry tiles, and I am loathe to leave one side of the staircase unsupported until the floor is re-instated. Also, I'll want the floor to exert an upward thrust on the bottom of the newels, because otherwise they would drop down when I remove the supporting material. I've thought about jacking them back up with short trench struts... I'd welcome any constructive advice!

Thanks
- Tim

 

[TimM]

any ideas?

 

[marshman]

dig out the hall but leave the bits under the newels, then jack / prop the stairs up about 3 foot back from the newels,
remove what's left under the newels, then blind with sand up to your jacks, then slid dpm under the newels to end of hall,
leaving the rest piled up near the jacks, lay 2 engineering on 1&1 sand & cement under newels to required height,
next day lower stairs and finish laying dpm.