The two-part standard at a glance
AS/NZS 2566 is the joint Australian/New Zealand standard for buried flexible pipelines — pipes that carry load by deforming and mobilising the surrounding soil, rather than by being rigid enough to resist it alone. That covers PVC, PE (HDPE), GRP, and similar thermoplastic and composite pipes. It is published in two parts, and they answer two different questions:
- AS/NZS 2566.1 — Part 1: Structural Design. The engineering. How to work out the loads on the pipe and check that it will perform: deflection, buckling, and ring-bending strain.
- AS/NZS 2566.2 — Part 2: Installation. The construction. How the pipe must actually be put in the ground: trench, bedding and embedment, compaction, and post-installation deflection testing.
| AS/NZS 2566.1 | AS/NZS 2566.2 | |
|---|---|---|
| Subtitle | Part 1: Structural Design | Part 2: Installation |
| Answers | Will the pipe perform? | How do we put it in the ground? |
| Used by | Designers / structural & civil engineers | Contractors, site engineers, inspectors |
| Key content | Loads, deflection (modified Iowa), buckling, strain, soil modulus E′ | Trenching, bedding & embedment, compaction, field deflection limits & testing |
| Life-cycle stage | Design & documentation | Construction & commissioning |
You design to Part 1. You build and inspect to Part 2. A calculation that passes Part 1 is only valid if Part 2 is followed on site — because the design assumed a particular quality of embedment and compaction that only the installation can deliver.
Part 1 — Structural design (the calculation)
AS/NZS 2566.1 is where the numbers happen. It takes the loads acting on a buried pipe and checks the pipe against three limit states. If you have used our AS2566 calculator, everything it computes lives in Part 1:
- Deflection — the vertical shortening of the pipe ring under load, via the modified Iowa formula. This is almost always the headline check. See our step-by-step deflection worked example.
- Buckling — resistance to inward collapse of the pipe wall under external pressure.
- Ring-bending strain — the bending strain in the pipe wall as the ring deflects, checked against an allowable strain for the material.
The single most influential input in all of this is the effective soil modulus, E′ — the stiffness of the soil around the pipe. It matters more than the pipe's own stiffness for most installations, which is exactly why installation quality (Part 2) is so decisive. We cover the subtleties of E′ in The E′ Soil Modulus Problem in AS2566.
Part 1 is the 1998 edition, incorporating Amendment No. 1 (2017). When people write "AS2566" with no suffix, they almost always mean Part 1 — it is the part engineers reference day to day.
Part 2 — Installation (the construction)
AS/NZS 2566.2 governs what happens in the trench. A flexible pipe relies on the soil beside it to carry load, so how the pipe is bedded and how well the embedment is compacted is not a construction detail — it is a structural input. Part 2 sets out:
- Trench geometry — width and support conditions.
- Bedding and embedment materials — the classes of material placed under, beside and over the pipe.
- Compaction — the density that must be achieved, which is what turns an assumed E′ into a real one.
- Field deflection — the allowable installed deflection and how it is measured and verified after backfill.
This is where the well-known GRP deflection tables live — for example, the allowable deflection limits many engineers search for as "AS2566.2 Table 5.6". Those installation limits belong to Part 2, not Part 1, which is a frequent point of confusion. (A dedicated article on the Part 2 GRP deflection limits is in preparation.)
Which part applies to your task?
A quick way to place any AS2566 question:
- "What deflection / buckling / strain will the pipe see?" → Part 1.
- "What soil modulus / bedding class do I assume?" → Part 1 uses it; Part 2 delivers it.
- "How wide is the trench, and how do I compact the embedment?" → Part 2.
- "What is the maximum deflection allowed once it's in the ground, and how is it measured?" → Part 2.
Reading a Part 2 installation deflection limit as if it were a Part 1 design output — or vice versa. Design deflection (Part 1) is the value you calculate; allowable field deflection (Part 2) is the acceptance limit you test against on site. They are related but not the same number, and they come from different parts of the standard.
How they work together on a real project
On a typical buried pipe job the two parts are used in sequence, then close the loop:
- Design (Part 1). Calculate loads and check deflection, buckling and strain — assuming an embedment material and compaction level, giving an assumed E′.
- Specify (Part 1 → Part 2). Translate that assumption into a construction specification: the bedding class and compaction Part 2 requires to actually achieve the E′ you designed with.
- Install (Part 2). The contractor builds the trench, beds and embeds the pipe, and compacts to the specified density.
- Verify (Part 2). Field deflection is measured after backfill and checked against the allowable installed limit. If it passes, the Part 1 design assumptions have been realised.
Skip or under-deliver on step 3, and the elegant Part 1 calculation is worthless — the pipe simply won't have the soil support the numbers assumed.
Summary
- AS/NZS 2566.1 = structural design: deflection, buckling, strain, soil modulus E′.
- AS/NZS 2566.2 = installation: trench, bedding, compaction, field deflection limits and testing.
- Design to Part 1; build and inspect to Part 2. Neither stands alone.
- Most day-to-day "AS2566" design work — and this site's calculator — is Part 1. GRP and other installed deflection limits sit in Part 2.
See an error in this article? Contact us — we review every correction against the standard.