Pipe bursting: replacing the whole line through two pits

The idea

The old sewer line is used as a guide path for its own replacement. A finned, cone-shaped bursting head is winched along the old pipe. Because the head is wider than the bore, it cracks the old pipe apart and pushes the fragments out into the soil as it moves. Coupled to its tail is the replacement: one unbroken run of high-density polyethylene, butt-fused from sticks before the pull begins. When the head arrives at the receiving pit, the new pipe lies in the old pipe's exact bed.

Static and pneumatic bursting

In static bursting a hydraulic unit in the receiving pit pulls the head with a chain of steel rods or a cable, with 20 to 60 tons of force on lateral-sized rigs, enough to split clay, cast iron, concrete and PVC. In pneumatic bursting a percussion hammer inside the head does the breaking while a winch keeps tension on the line. Static rigs dominate lateral work because they are compact, quiet and controllable; pneumatic systems are common on larger mains and brittle pipe.

The pits

Bursting calls for a launch pit and a receiving pit. On a house lateral one sits at the foundation or cleanout where the line exits, the other at the curb or over the main. Each is roughly 3 feet by 4 feet at the surface and as deep as the pipe, which for most laterals is 3 to 8 feet. Everything between them — lawn, driveway, patio, trees, the neighbor's fence — is undisturbed. Where a lateral connects to a main under the street, the exit pit is a small cut at the curb rather than a trench down the road.

The new pipe

HDPE comes in sticks that the crew fuses on site into a single seamless length; a butt-fused joint is as strong as the pipe wall on either side of it. It is flexible enough to follow the old route, strong enough to survive the pull, and once in place it does not corrode, does not crack with ground movement, and offers roots no joint to enter. Gravity sewer laterals are normally installed in SDR 17 pipe (wall thickness one seventeenth of the diameter), and the Plastics Pipe Institute rates properly installed HDPE for a 100-year service life. Bursting also permits upsizing: fit a bigger head and a 4-inch lateral comes out as 6-inch, useful where bathrooms, units or a commercial kitchen were added after the original line went in.

How long it takes

The pull on a 50- to 100-foot residential lateral typically runs 30 to 90 minutes. The rest of the day is pit excavation, fusing the pipe, connecting the new line at the house and at the main, the city's tie-in inspection, and backfilling and compacting the two pits. Water use is paused for a few hours while the connections are open. On a 300-foot main the pull may run a few hours and the job two days, with the street open the whole time.

When bursting is the right call

• The line has collapsed, flattened or bellied so a liner cannot restore it.
• The pipe has lost grade at a joint and needs to be relaid rather than rebuilt.
• The material is Orangeburg or badly deteriorated cast iron that will not hold a liner.
• The lateral needs to be a larger diameter than it is.
• The run is long, deep, or under something that must not be dug up.

Where it does not work

Bursting follows the old alignment, so a line that was laid with a bad slope will come out with the same bad slope. Pipe encased in concrete, runs with too many fittings, or shallow lines with a gas or water service within a foot or two can stop a bursting head or damage the neighbor. And the old pipe must be passable by a cable; a complete crush at one point can sometimes be opened from a small pit so the pull can proceed, but not always. The pre-inspection settles all of this before the equipment arrives.

Common questions about pipe bursting