We do not have a weight limit, but we do have a clause that says if anyone damages the road beyond normal wear and tear, they must pay for the repair.  The trouble with a clause like that in your case would be defining "normal wear and tear," documenting the extent of the damage, and proving who was responsible for it.  You could specify a weight limit with exceptions for things like fuel deliveries, snow removal equipment, etc.  We have debated imposing a flat fee any time someone does construction, but have never gotten that one to pass.