In my experience with them... dump truck beds vary... some are equipped for soil, some are ready for big rocks (boulders)... some are great for sand and gravel... ask dump truck co.'s about that... perhaps if you have a truck, bring it by and talk to a dump truck co. owner.
I know sand can be hauled 100+ miles one way with the big semi truck dump trailers, and typcically stay busy 6 days a week.
They dump it at various yards, and then regular dump trucks are loaded with the sand and it's hauled to the sites by them. Gravel is handled the same way. Soil operations vary. Soil is where having a liner inside the box can help. The dump truck biz picks up substantially anytime storms do damage. Like anything, there's good money in it, if you got the right customers.