The paper presents the results of field and laboratory investigations carried out on two test embankments located on soft soils in north-western Poland. Comprehensive investigations including observations of test embankments and laboratory testing have been conducted in order to study the behaviour of the consolidation process in soft subsoil. This paper presents the analysis of factors determining the assessment of the deformation process of soft subsoil. The analysis was focused on determining non-linear deformation-stress characteristics used for modelling the deformation of soft subsoil under the earth structure. Deformation characteristics obtained in laboratory tests were compared with field measurements, which included vertical and horizontal displacements, as well as pore pressure dissipation. Based on analysis of field observations and laboratory tests results, the characteristics determining the consolidation process were elaborated.