[Leo.G (Leo)]

A question for the experiences pier installers.
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Embedded stainless steel threaded rod or dyna-bolts?



I've dug a 600x600x700mm deep hole, right down into clay. I've put around 75mm of course gravel in the bottom which will be tamped down into the clay and I'll also be pouring in one or two bags of cement powder. I've done stuff like this before and know the gravel and cement will prevent the clayfrom drawing the moisture out of my block when I get to concreting.


I have a small section of weld mesh to put in also around mid point of the slab, the slab which will stop 150mm from the top and I'll be putting 3 pre-drilled 600mm x600mm pre-cast concrete blocks down on top after the concrete has cured. This is so if I get complaints from the department of housing I can remove the top 6 inches, grind the threaded rods off and fill with top soil should I ever be instructed to remove the pier (I'd fight that and win but I like to be prepared)
I've also driven 4 x 1000mm lengths of 19mm rebar down, one in each corner of the pit (diagonally from inside corners), radiating out at approximately 40-45 degrees on 2 corners and 60 degree on 2 corners because I know there's an electrical conduit running close though it is at regulation depth of 500mm and these rods are starting out deeper than that but to be safe I drove them in at a slightly steeper angle.


My intent is to use 16mm threaded stainless steel rods to secure the pier and I was going to fabricate a triangular frame out of 2" angle iron and set that in the hole with the rods coming up vertically for the pier to slip over but with different expansion rates of concrete and steel I don't want the slab to crack.


Plan B: I'm contemplating cutting a steel ring matching the piers mount size and hole locations and suspending it over the hole with the rods dropping down into the concrete with retaining nuts and large washers at the bottom to give it a little more surface area for the concrete to cover. To have room to get concrete in pit (hand mixed in wheelbarrow) without disturbing the position of the stainless threaded rod I'll weld up a tripod out of any scrap water pipe I have laying around and with the rods each being 1 metre long I should be able to hang them securely perpendicular and they should remain in the correct position while I pour the concrete (I can weld the supporting top plate to the tripod so nothing moves). I can put heavy scraps of 12-16mm steel at each base to give it weight, I have plenty laying around to use as scrap.


I see many people using dynabolts to do this, were I using solid concrete slab I may consider this but the 6 inches of pre-cast at top layer (3 x50mm x 600x600 slabs). I've used dynabolts and chemsets to secure car hoists (I've installed a lot of car hoists, I used to manage a company which specialised in motor garage equipment) and they are a pain when ANYTHING goes wrong, it's OK in a mechanical workshop when you can move the hoist the few regulation inches from the failed mounting and try again, not so easy on a small slab not that there's regulation on what I'm doing but not a lot of spare room either.
Should I dyna-bolt the 3 slabs together?



Any suggestions?