Enter the old and new pipes' outside diameters, the expander oversize and the run length. The calculator gives the expander size, the soil pushed aside per metre and over the run, and the upsizing ratio. For a 150 mm pipe replaced with 168 mm pipe and a 10 percent oversize, it shows a 185 mm expander, ×1.23, 9.2 litres per metre and 183 litres over 20 m.
- Expander diameter is the new pipe's outside diameter times one plus the oversize percentage.
- Displaced soil is the ring between the expander circle and the old pipe's outside circle, converted to litres per metre.
- The upsizing ratio is expander diameter divided by the old pipe's outside diameter; above 1.5 the tool suggests asking the installer.
- The drawing is to scale and animates the expander growing from the old pipe's size to its own.
- It is geometry only: it does not predict heave, which depends on depth, soil and method.
Upsizing & Displacement Calculator
01 /What do I enter in the calculator?
Four numbers, all editable, and the result updates as you type.
| Input | Default | Allowed range | Where to find it |
|---|---|---|---|
| Existing pipe outside diameter | 150 mm | 40 to 900 mm | Camera report, a measurement at a cleanout or pit, or the pipe's nominal size |
| New pipe outside diameter | 168 mm | 40 to 900 mm | The print line or quote; HDPE is made to a fixed outside diameter |
| Expander larger than the new pipe by | 10% | 0 to 40% | Ask the installer what expander they use |
| Length of the run | 20 m | 1 to 500 m | Distance between launch and receiving pits |
Use outside diameters, not nominal sizes. A "6-inch" pipe can have quite different outside diameters depending on material and sizing series, and the difference matters to the result. If you only know the nominal size, the answer is a rough guide until the installer confirms the real numbers.
02 /How does the calculator work out the displacement?
The maths is simple circle geometry, done in the same order the tool runs it:
- Expander diameter
New outside diameter × (1 + oversize). With the defaults: 168 × 1.10 = 184.8 mm, shown as about 185 mm.
- Displaced area
π/4 × (expander² − existing OD²), with both in metres, and never less than zero. Defaults: π/4 × (0.1848² − 0.150²) ≈ 0.00915 m².
- Litres per metre
Area in square metres × 1,000. Defaults: about 9.2 litres of soil pushed aside for each metre of run.
- Whole run
Litres per metre × run length. Defaults: 9.15 × 20 ≈ 183 litres.
- Upsizing ratio
Expander diameter ÷ existing outside diameter. Defaults: 184.8 ÷ 150 ≈ 1.23, shown as × 1.23 and "23% larger than the existing pipe".
The ratio gets a badge: ok up to 1.25, caution above 1.25 up to 1.5, and avoid above 1.5. Above 1.5 the result adds a line about large upsizing, suggesting you ask the installer how they will manage ground movement, pulling force and nearby utilities. If displacement comes out under 0.05 litres per metre, the headline reads "Little net displacement" instead of a number.
03 /What does the drawing show?
The cross-section is drawn to scale, with the largest circle fitted to the frame. It overlays four circles: the existing pipe, the new pipe, the expander, and a shaded ring for the displaced zone. When the result updates, the expander circle animates from the size of the old pipe out to its own diameter in under a second, showing the ground being pushed outward. Labels give the existing, expander and new diameters in millimetres.
Below the result the tool adds two reminders: the soil is compressed outward, not removed, and fragments of the old pipe stay in the ground around the new one.
04 /What do typical cases look like?
| Existing OD | New OD | Oversize | Length | Expander | Per metre | Whole run | Ratio |
|---|---|---|---|---|---|---|---|
| 150 mm | 168 mm | 10% | 20 m | 185 mm | 9.2 L | 183 L | ×1.23 ok |
| 168 mm | 168 mm | 10% | 20 m | 185 mm | 4.7 L | 93 L | ×1.10 ok |
| 115 mm | 125 mm | 10% | 20 m | 138 mm | 4.5 L | 89 L | ×1.20 ok |
| 140 mm | 168 mm | 10% | 18 m | 185 mm | 11.4 L | 206 L | ×1.32 caution |
| 115 mm | 168 mm | 10% | 20 m | 185 mm | 16.4 L | 329 L | ×1.61 avoid |
| 200 mm | 250 mm | 10% | 80 m | 275 mm | 28.0 L | 2,238 L | ×1.38 caution |
Size-for-size bursting still displaces soil because the expander is larger than the host. And the ratio, not the absolute size, is what climbs fast when a small pipe is replaced with a much larger one. For the context behind each case, read upsizing by pipe bursting.
05 /What can this calculator not tell me?
It cannot tell you whether the ground will heave, whether a nearby utility will be affected, or whether the pull will succeed. Those depend on depth, soil type and compaction, groundwater, the head type, the installer's method and what is close to the line. The US EPA fact sheet on bursting notes that critical conditions for ground displacement include a shallow pipe, much larger replacement pipe and deteriorated utilities within two to three diameters.
- Depth: the same displacement near the surface is far more likely to lift a lawn or slab than at depth.
- Soil: compressible backfill absorbs displacement close to the pipe; dense or rocky ground pushes it further.
- Overcut trade-off: a larger expander lowers friction on the new pipe but displaces more soil.
- Nearby services: a volume in litres says nothing about where a gas service lies.
Pair the result with the Pipe Bursting Fit Check, which weighs depth, soil and utilities, and with risks and problems. Bring both to your installer, or send them with a quote request.
FAQQuestions people ask
What oversize do bursting heads use?
It varies by installer and job. The calculator defaults to 10 percent; the PPI handbook describes an overcut of about half an inch around the pipe as a way to reduce friction.
Why does the calculator use outside diameters?
The soil only sees the outside of the old pipe and the outside of the expander. Inside diameters would understate the ring of ground being moved.
Is 9 litres of displaced soil per metre a lot?
It is a modest amount in compressible ground at normal depth. Where the pipe is shallow or close to other services, even small volumes need care.
Why does the drawing animate?
The expander circle grows from the old pipe's size to its own to show the soil being pushed outward as the head passes. It is illustration, not a simulation of ground movement.
Can I use the calculator for a water service?
Yes. The geometry is the same for any host and new pipe; enter the outside diameters of the old service and the new pipe.
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