Hot take: concrete thickness might matter less than soil compaction

I was reading through an old FEMA manual from 1979 and found a stat that threw me: they said 12 inches of concrete is overkill if your backfill is loose dirt. They claimed proper compaction matters more than an extra 4 inches of wall. I re-read it three times because everything I've seen online says thicker is better. Has anyone else run across this or is that old manual just wrong for today's standards?

3 comments

3 Comments

karenb971d ago

Has anyone checked if the old manual was talking about reinforced vs. unreinforced concrete? @susansingh pointed out that a crack showed up in six months, and rebar placement might be the missing piece here. Thicker walls without steel are just more brittle mass waiting to fail on unstable ground.

grant4781d ago

@susansingh nailed it. Thicker walls just mean a bigger, heavier problem when the ground underneath gives out. Guess my only hope is to compact dirt better than I pack my own lunch.

susansingh1d ago

Oh man, that actually tracks with what I saw on a job site last year. We poured a 14 inch wall on fill that wasn't compacted right and it cracked right through the middle within six months. The compaction is what keeps everything from settling and pulling apart. Thicker concrete can't fix bad dirt underneath, it just gives you a heavier slab to break later. That old manual might be onto something, people forget foundations are only as good as what's under them.