Tenn. Code Ann. § 54-9-126

In receiving and letting the contracts, the commissioners shall at all times include the laying of all drain tiles or pipe for the draining of the roads, after the drain tiles or pipe have been placed on the road, by the county, and further include the tamping or packing of the dirt around the pipe or drain tiles, without additional cost to the county where they are being placed under fills for drainage of the roads.