Converting oedometer modulus to Young’s modulus

Updated: 2026-08-04 · ISKRIT

An oedometer prevents lateral strain, so the modulus it measures is a constrained modulus, not Young's modulus. Using one in place of the other overestimates stiffness by a third to a half for ordinary soils.

The relation

For an isotropic elastic material under zero lateral strain:

E = Eoed · (1 + ν)(1 − 2ν) / (1 − ν)

The factor is always below 1 for ν between 0 and 0.5, so the correction always reduces the modulus. It falls to zero as ν approaches 0.5, the incompressible limit, and this is why the conversion becomes unusable for saturated clay under undrained conditions.

Typical Poisson ratios

These are drained values for effective-stress analysis. A laboratory that has measured ν on the material should use its own number, and the calculator accepts one.

Worked

Eoed = 6.14 MPa for a loam with ν = 0.35 gives

E = 6.14 · 1.35 · 0.30 / 0.65 = 3.83 MPa

The uncorrected value is 60 % higher than the corrected one. On a settlement calculation that difference is the whole answer.

What other traditions do instead

Russian practice under GOST 12248 does not use the elastic relation at all. It applies an empirical coefficient β by soil type, 0.8 for sand down to 0.4 for clay, calibrated so that laboratory oedometer results reproduce plate load moduli measured in the field. The two routes answer different questions: β carries an empirical correction for sample disturbance and scale, the elastic factor carries only the boundary condition. Neither ASTM D2435 nor EN ISO 17892-5 defines a β, which is why an international report quoting a modulus of deformation without saying which route it took is ambiguous.

Questions

Which value goes into a settlement calculation? That depends on the method: one-dimensional settlement formulas expect the constrained modulus directly, elastic half-space formulas expect E.

Can ν be back-calculated from the test? Not from a standard oedometer, since lateral stress is not measured unless the cell is instrumented for K0.

The consolidation tool applies the factor and shows both moduli when the international standard is selected.