In this paper deformation parameters of organic soil gyttja, were taken into the consideration. The organic soils are usually located in the river valleys and as a subsoil under engineering constructions, e.g. in the city. Gyttja’s, because of their large compressibility, small shear strength and difficult to evaluate permeability create a problem during calculating and modeling the foundation of the engineering construction. The stress-strain relationship in gyttja is hard to predict, because of the non-linear deformation parameters and variability of strength parameters. Therefore, it is very important to properly determine deformation parameters of organic soils on the basis of in situ and laboratory tests. In this paper, the laboratory test results, obtained on soil samples type A, and in situ dilatometer Marchetti test are presented. Oedometric modulus obtained from laboratory tests is verified with the in situ results. Determination of deformation parameters of gyttja, based on in situ and laboratory tests, lets to predict stress-strain characteristics for safety and failure-free work of the designed engineering construction.

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