like yourself, I find it hard to believe that a pallet plugging the pipe would cause the pipe to wash out. The pallet didn't shut-off the flow to cause more pressure on the pipe. And if it did, that pressure situation would happen in an extreme rain event anyway. In regards to the pallet partially blocked the pipe, causing a swirling effect, I would say what about a trash guard's effect that may do the same. Would that have made it go? Or if the pipe was so touchy to erosion from a plugging situation, perhaps he should have installed something to safe guard himself as well as you.
Then you say he installed it with a dozer, compacting and all. Hmmmmm, don't sound good. Sure, some soils are very forgiving and easy to compact for ponds. And some heavy equipment operators are excellent in what they do. His equipment broke down, and he decided to install a different way. That was his choice.
It all don't sound right or good to me. However, I am not a professional dirt mover, just a common sense guy who does his own stuff out of necessity. Wish you the best in getting it straightened out.
