cast against secant wall

[Pringlemeir]

I have a postage stamp of a construction site, where we are placing a 7m deep chamber. We have used secant shoring walls with the intent of casting against the shoring. During my site visit i noted hat the shaving of the secant walls is very rough leaving some hollows and gaps 150 to 200mm deep (6-8"). Originally we had blind side water proofing but that just got deleted from the scope, so here is the question... What is the effect of casting a new concrete wall against this rough surface? DO I worry about bonding creating additional cracking in my new wall? can I prevent it by adding a poly slip sheet? Do I need to parge or foam the wall to smooth it out?

 

[Ron]

Yes, those gaps and divots will create restraint and increase cracking. Use foam or parge, not plastic. Plastic will deform into the gaps and create restraint

 

[Pringlemeir]

After smoothing the wall, would casting against it still create bond, or do we think the secant concrete is weak enough to not be an issue? and my chamber can shrink vertically without restraint? DO people usually use a liner material when casting against a secant wall?

 

[Ron]

There will always be restraint when casting against a secant wall. You just want to mitigate the random restraint caused by anomalies in the wall.