E′ — the effective modulus of soil reaction — is the single most influential input in an AS2566.1 deflection calculation. This page is a practical value reference. For why the standard's handling of E′ trips engineers up, read the companion article The E′ Soil Modulus Problem in AS2566; to see E′ used end-to-end, see the deflection worked example.
The tables below reproduce selected, representative values from AS/NZS 2566.1 Table 3.2 for quick reference — they match the presets built into the Buried Pipe Calc calculator. Always confirm the value for your exact material and compaction against your current copy of the standard before relying on it in design.
E′e vs E′n — one minute
AS2566.1 uses E′ for two distinct things, and they must be sourced differently:
- E′e — embedment modulus. The stiffness of the imported material you compact around the pipe. Read from Table 3.2 (below).
- E′n — native soil modulus. The Young's modulus of the trench-wall soil. Ideally from geotechnical data; indicative values are below.
The two combine through the Leonhardt correction factor ζ to give the effective E′ used in the deflection formula — see applying these values below.
Embedment modulus E′e (Table 3.2)
These apply to the compacted embedment zone around the pipe. The value depends far more on compaction than on the material label — the same sand/gravel spans 5 to 10 MPa across the compaction range.
| Embedment material | Placement / relative density | E′e (MPa) |
|---|---|---|
| Fine-grained soil | Dumped / uncompacted | 1 |
| Fine-grained soil | Compacted, D ≈ 85% | 2 |
| Fine-grained soil | Compacted, D ≈ 90% | 3 |
| Sand / gravel | Compacted, D ≈ 85% | 5 |
| Sand / gravel | Compacted, D ≈ 90% | 7 |
| Sand / gravel | Compacted, D ≈ 95% | 10 |
| Single-size gravel | Compacted, D ≈ 95% | 14 |
| Well-graded gravel | Compacted, D ≈ 100% | 20 |
Most-assumed value: compacted sand/gravel at D ≈ 85% → E′e = 5 MPa is the value most commonly adopted in Australian practice. Select for the compaction you can realistically guarantee and inspect on site, not the best case.
Native soil modulus E′n
Use these only as indicative starting points for the trench-wall soil — a geotechnical investigation (SPT correlations, pressuremeter, published correlations) is preferable. Do not read native soil values from the embedment column above.
| Native soil group (USCS) | Condition | E′n (MPa) |
|---|---|---|
| Fine-grained / organic | Soft — not reliable | ≈ 0 |
| CL, ML (fine-grained, <25% coarse) | D ≈ 85% | 1 |
| CL, ML (medium plasticity) | D ≈ 90% | 2 |
| GM, GC, SC, SM (>12% fines) | D ≈ 85–90% | 3 |
| SW, SP, GP (sand, <12% fines) | D ≈ 85% | 5 |
| SW, SP, GW, GP (sand / gravel) | D ≈ 90–95% | 7 |
| GW (graded gravel) | D ≈ 95% | 10 |
| GW (single-size gravel) | D ≈ 95% | 14 |
| Rock (competent) | — | 20 |
Applying these values
Where the trench is narrow relative to the pipe, native soil influences the effective modulus. AS2566.1 combines the two via the Leonhardt factor:
E′e — embedment modulus (Table 3.2, above)E′n — native soil modulus (indicative values above / geotech)B/De — trench width ÷ outside diameter- Soft native soil (E′n < E′e) reduces the effective E′ below the embedment value — skipping ζ here is unconservative.
- Groundwater at pipe level: Table 3.2 Note 1 halves the embedment E′e.
- Compaction dominates. The jump from D ≈ 85% (5 MPa) to D ≈ 95% (10 MPa) sand/gravel doubles the soil support — a bigger lever than pipe stiffness class.
Select E′e and E′n in the calculator and it applies the Leonhardt correction and groundwater reduction automatically, showing the full working.
Summary
- E′e = 5 MPa (sand/gravel, D ≈ 85%) is the common default; the range spans ~1 MPa (uncompacted fines) to ~20 MPa (well-compacted graded gravel).
- Source E′n separately for the trench wall — don't reuse the embedment value.
- Combine via the Leonhardt ζ factor; reduce E′e by half for groundwater at pipe level.
- Confirm every value against AS/NZS 2566.1 Table 3.2 for your specific material and compaction.
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