Don't know where you're located, but I'll be conducting several live-fire cooking workshops this winter, at Fort Boonesborough State Park, in Kentucky. Dutch oven cookery is an integral part of that.
If you're interested, contact me privately at firstname.lastname@example.org.
As others have said, it sounds like you're using too many coals and cooking too long. It also helps if you follow a few rules-of-thumb, all of which replicate the conditions found in your home oven.
1. Use a separate cooking dish. F'rinstance, if you're making a cobbler, put it together in a baking dish, and put that in the Dutch oven.
2. Use a trivet in the bottom of the oven. Having that air cushion can really help. Doesn't have to be much. I use 3/16 square stock and bend it to shape. Some people just use a few small stones.
3. Always pre-heat the oven. You'd think this would be obvious, but it's amazing how many people don't do it.
4. While it's often not feasible, try to not let hot coals actually touch the bottom of the oven. That can cause hot spots, which lead to burning. Hot spots are one of the reasons a trivet helps.
Until you develop a feel for Dutch oven cooking, you're better off using charcoal briquettes. And follow the rule of three: take the # of the oven. Subtract three. Use that many briquettes on the bottom. Add three. Use that many on top. This will give you a 350F oven every time.
It also helps to replicate hearth cooking, because raw ground, particularly if it's damp, can really suck the heat out of the coals. We use
16" square pavers. Arrange your bottom coals on the paver, cover with the oven, and you're good to go.