Let me see if I understand what happened. You dug a hole then instructed the hearthlings to build a road inside of it?
If that is the case you may have encountered a couple of problems.
The most common is that they dug the ground to place the road. The ladder to access it goes down to the new “lower” floor. When they build the road the lower part of that ladder, and any thing based on that “lower” floor, gets covered by the road. The hearthlings can no longer access the base of said ladder and can not remove it.
The way round this problem: Build only half the road first, placing the ladder in the untouched part. Once finished, change the ladder to the already built side and build the remaining half.
If this is not the problem you encountered, please explain a little more what happened, and i’ll try to see if i can explain/solve it.