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Oedometric Modulus

If the results from oedometric test are represented in terms of oedometric curve (Δε = f(Δσ_ef )), it becomes evident that for each point on the curve we receive a different ratio σ_ef  /ε.

Determination of oedometric modulus E_oed

If the stress-strain curve is replaced for a certain interval of two neighboring stresses σ_1ef - σ_2ef by a secant line, it is acceptable to assume a linear behavior of soil within this interval and represent the soil compressibility by as Δσ_ef/Δε - called the oedometric modulus of deformation. The oedometric modulus of deformation is, therefore, a secant modulus linked to a certain stress interval σ_1ef - σ_2ef selected on the stress-strain diagram Δε = (Δσ_ef ):

In general, the oedometric modulus of deformation E_oed tends to decrease its value with the increasing stress interval. Therefore we should consider for each layer a specific value of E_oed pertinent to a given stress interval (from original to final stress state). This is reflected in the program by the way of inputting E_oed, where it is possible to specify for each soil the respective oedometric curve (σ_ef/ε diagram).

Practical experience, however, suggests (e.g. for clays) several orders of magnitude difference between the value of E_oed derived from the deformation modulus E_def and that provided by the in situ measured loading curve.

The relation between E_def and E_oed is provided by:

Approximate range of values of oedometric modulus of deformation E_oed for individual soils and typical stress range (prof. I. Vanicek: Soil mechanics):

Literature:

Vanicek, I.: Geomechanika 10: mechanika zemin. 3^th edition, Prague, CTU, 2000, 229 s., ISBN 80-01-01437-1.