Pits and site layout for pipe bursting: where the holes go and why

01 /How many pits does a pipe bursting job need?

The minimum is two per run: one to launch and one to receive. Everything else is driven by what is along the line. The EPA's 2006 fact sheet lists insertion pits as a disadvantage of bursting compared with lining, unless a manhole-to-manhole system is used, and its implementation steps include disconnecting services and removing impediments, both of which usually mean excavations.

The PPI handbook recommends placing pits where excavation is needed anyway, at manholes, valves, lateral connections and fittings, and using one insertion pit to launch in two directions where possible to cut total digging.

02 /How big is a launch pit, and why?

A launch pit has two parts. A flat section at pipe depth lets the crew line up the head with the centreline of the old pipe. A sloped section lets the new pipe curve from the surface down to that depth without being bent tighter than it can take. The PPI handbook says PE can be cold bent to roughly 25 to 30 times its outside diameter, which is the number that sets the slope length.

The handbook gives a worked example for a large main: for 18-inch DR 17 pipe, a minimum insertion shaft length of 12 times the new pipe diameter for the flat part plus 2.5 times the shaft depth for the sloped part. Residential pits are much smaller, but the logic is the same: deeper pipe and larger pipe both mean longer launch pits.

• The pit is usually trimmed so the crown of the old pipe is removed to its spring line, giving the head a clean start.
• Its width depends on pipe size and room for workers to connect the head safely.
• Where the fused string cannot be laid in line with the pipe, the flexibility of HDPE lets it come in at an angle, within its bend radius.

On a house lot the launch pit is often the biggest hole of the job, and where it goes is a real decision. Launching beside the foundation keeps the long sloped entry in the back yard but puts the heaviest digging near the footing and any gas meter. Launching at the property line and pulling toward the house moves that slope to the front yard or boulevard and puts the compact receiving pit by the wall. Ask the installer why they chose one direction.

03 /What goes into the receiving pit?

The receiving pit holds the pulling unit and must survive the force it applies. The PPI handbook explains that the winch or puller thrusts against the manhole wall or one side of the pit, so a thrust block or plate is needed to spread that force, and the soil behind it must resist the load with a margin of safety.

• Room to work. The puller, rods or cable drum, and space to separate the head from the new pipe when it arrives.
• A strong back wall. Undisturbed soil or a built thrust structure; a pit dug in loose fill may need more support.
• Dewatering. The handbook calls for dry pits; a sump in one corner handles rain or a slightly high water table.
• Inspection space. The head end of the new pipe is examined here for gouges after the pull.

04 /How much yard space does the pipe lay-down need?

A continuous fused string needs a clear strip roughly as long as the run behind the launch pit, or a curving path the pipe can follow within its bend radius. The EPA names the area available for pipe lay-down as one of the factors that limits how long a run can be, because it caps the length of pipe that can be fused and laid out.

Ask to see the lay-down path on the site sketch. It tells you which parts of the lawn, driveway or lane will be occupied, and for how long.

05 /What safety and locate rules apply to bursting pits?

Bursting pits are excavations like any other. The Canadian Centre for Occupational Health and Safety says trenches 1.2 m (4 ft) deep or greater require a protective system unless the excavation is made entirely in stable rock, and that pipe, spoil, tools and other materials should be kept at least 1 m from the edge. Provincial occupational health and safety rules set the legal requirements for the crew; confirm the specifics in your province.

Before anyone digs, buried utilities must be located. In Alberta, Utility Safety Partners runs the one-call service; its locate page says a minimum of three full working days' notice is required for a routine request and five for large project tickets, and that you are not clear to excavate until all utilities have been located. Other provinces have their own services, listed through ClickBeforeYouDig. One-call marks utility-owned lines; private lines such as a garage feed or gas line to a barbecue may need a private locator.

06 /What should a pit plan on a bursting quote show?

A quote you can hold an installer to includes a simple drawing. The PPI handbook's submittal list for public projects includes site layout, pit locations and dimensions, shoring design, bypass plan, pipe storage and restoration; a residential version can be one page.

1. The route of the old pipe, with depth at each end if known.
2. Every pit, numbered, with its purpose and the surface it breaks: lawn, concrete, pavers, asphalt.
3. Where the fused pipe will be laid out and for how long.
4. Located utilities near each pit and near the route.
5. What happens, and at what price, if an unplanned pit is needed.
6. How each pit is backfilled, compacted and restored, and when.

Pit count drives price. The pipe bursting cost page shows each pit as its own planning line. The Fit Check adds a point for three or more connections because each needs a pit, and the sewer lateral guide shows where pits usually land on a house lot. When you have a layout in mind, request quotes and ask each installer to sketch theirs.

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