One of the most important soil parameters is deformation modulus. In Ukraine during recent years increasingly using oedometer tests when assessment the soil compressibility. However, the reference value of soil deformation modulus is its determination by plate loading tests with plate area not less than 0.5 m². The deformation modules E_oed significantly lower than E_PLT.

Methods analysis and features of oedometer soil test specimens showed that more than 20 factors may affect the results but two types of factors have the crucial influence to the determination of E_oed: sample crumbling on contact with oedometer stamps, the influence of loading history and test time.

So the real values of E_oed can be obtained directly by measuring of soil samples deformation in the area that does not effected by plastic deformation (crumbling) and with correct selection of deformation stabilization criteria, which will depend on the depth of soil sampling.