6" mild steel 1/4" sidewall box tubing filled with dirt would take me about 10 minutes to cut 4 times. I could get through that steel barrier before anyone would know I did it. Just need a torch, a 00 cutting tip and a BFH. Not bragging I just know what the fuck I'm doing. Been in the steel and related industries for about 35 years.
Two guys with Harbor Freight backpack torches with the biggest tips they could find and maybe half an hour could breach that with a man sized hole.Logistics issue solved. Hell give me a couple of weeks and I could get through it with a mill file. I want Concrete reinforced with embedded thick assed chain link.