I had an old boat trailer that got converted into a flatbed trailer. It had a 3500# axle on it if it was lucky. Probably rated less than that.
I took it out one day to get a load of *wet* garden top soil mix. This stuff easily weighs in at 1.5 ton per yard, maybe a bit more. I've carried 1.5 yard with this trailer with no problem before, though.
The rock and soil place generally loads you up with either a 1/2 or 1/3 yard loader. I told the guy in the shop I wanted 1.5 yards, so he calls out the kid to load me up. So, I wasn't really paying attention and told the kid I needed 3 scoops. He looks at the trailer, looks at me funny, says "ya sure?". Should've been my first clue.
I say, "yep, load 'er up". The first load goes on no problem. I motion for a second load, and the trailer starts to squat down a bit, and I motion for a third load. Once again he looks at me twice, and I motion to go ahead. Jeez, what was with this kid?
As the load starts dropping, I watch in slow motion as the top of my wheels start to bend in towards the center of the trailer.
Yep - bent axle.... Wheels were now rubbing on the sides of the trailer... It turns out the kid had grabbed the 1 yard loader instead of the 1/2 yard. Guess what? 9000 lbs on a 3500 lb axle - well, the axle loses!
I grabbed a shovel and started shoveling the dirt back out the back of the trailer. Took it a while, but I got most of that last yard out, maybe some of the next. Then I pulled it over to their shop. Between a jack in the middle of the axle, a fork lift, and the weight of several big guys, we were able to somewhat bend the axle back in shape. Then I cut a little of the deck where the one tire was still rubbing, and I was good to go.
The kid really got a cussing out because he grabbed the wrong loader. I felt bad because it was partially my fault. They wouldn't take any money for the 2 or so yards I hauled away, after having bent my trailer.
I used that trailer for several more years before finally selling it for $250 more than I paid for it. I never did try to get more topsoil on it, though!