Floating Wall, thin concrete floor won't take nails?

I'm building a floating wall in my basement to simply "house" the plumbing for the washer and dryer I'm about to put down there. The wall will never be closed up.

I've discovered when nailing down the PT lumber the concrete is maybe 1/2" thick, and because of this the nails are not holding properly. This really became the case when I nailed in the 6" float nails (red arros). The nailing impact form those shook loose the 3" concrete nails (green arros). Any ideas on how to fix this.


It's a 110 year old home. The basement is by no means finished, so I get why it's so thin (it's not a living space).

 

Hindsight is 20/20. I would have attached the bottom plate with PL8X or equivalent adhesive rather than nails, but you didn't know the thin concrete existed. I still find it difficult to believe the concrete is only 1/2" thick, but it was probably poured over existing dirt many years ago without regards to forming it or digging it out properly.