I've been a bit of a nob and made the chases for too deep. God knows what I was thinking about, I should have known better but the damage is done. See drawing.
The walls are internal 100mm light concrete blocks (Thermalite) & the occassional LBC common bricks with 12 to 15mm render and a skim of plaster over the top. The chases are from ceiling to half way down each wall and around 60mm deep but in some places up to 70mm deep.
The idea was to chase deep enough for 2 x 22mm shower pipes, 1 x 15mm shower pipe and 1 x 15mm heating pipe all lagged, the area would then be repaired and tiled over.
Only after much of the chasing was done did I realise what I had done. Thankfully most of the chasing was done by carving the blocks with a wood chisel and very little hammer & bolster work. There are no sign of cracking on the reverse side of the walls, so hopefully I haven't disturbed what's left to much.
What I now need is a suitable way to repair the chases with out removing the pipes, that will hopefully put some strength back in the walls and corner.
I wondered if I left the pipes unlagged and made the repair with expanding foam whether that would be sufficient, I'd could tape the pipes so the foam didn't stick to them, and PVA the chases to provide better adhesion for the foam. I read somewhere that drywall adhesive was good for repairing chases especially if the surrounding area was not very sound.
Any advise would be much appreciated.