If an underground sewer line has proper slope and needs to be replaced, there are two options.
One, you can dig a new trench or two you can use a pipe bursting machine.
A pipe bursting machine pulls a new continuous piece of pipe through the old line. The old pipe is crushed and compacted into the walls of the surrounding trench.
The new pipe is then laid in the exact same location of the old line, without disturbing any of the landscaping, concrete or whatever might be on the surface.
Pipe bursting does require two entry points, one typically on the building and one at the connection to the county sewer. HDPE pipe used in pipe bursting in fused together.
That means there are really no joints except at the connection to the existing system. HDPE pipe is a better material for sewer as it is impact resistant, does not require a joint every 10 feet and does not get brittle over time.
HDPE is the number one material used in municipal infrastructure for gas and water, and now in the past ten years is growing in popularity as a preferred product for sewer replacement. HDPE piping is nearly 6 times the material cost of PVC and more labor intensive to fuse versus gluing PVC.
A trenchless installation depending on the situation can be less expensive that an open cut trench and there is minimal landscape work needed when the project is completed. HDPE pipe carries a better warranty than PVC and cast iron pipe, rated at over 100 years of projected lifespan.
Compared to other materials such as clay pipe and concrete pipe which is subject to cracking, HDPE has some flexibility and has the ability to expand and contract without cracking.