Holding polystyrene secant pile guide wall formers

[lemonbreath]

Hello all

I am looking for some practical advice regarding secant pile guide wall formers. Edge formwork is in place an timber straps (18mm ply) span from the side formers over each polystyrene block.

I would like to retain the blocks and prevent any lateral movement at the bottom where they meet 50mm concrete blinding. I am thinking of using a layer of concrete say 30mm or perhaps drill in some rebar. The thin concrete layer would also prevent concrete from the main pour getting under and lifting.

Am I being over cautious. Is it just a case of ensuring careful and slow placement of the concrete?

Thanks for any help.