Acta Scientiarum Polonorum

The paper presents an example of designing the consolidation improvement of the organic subsoil under expressway
by staged construction with preloading using vertical drains and geotextile. In the subsoil of road
embankment there are organic soils (peat, gyttja) with a thickness of 4.5 m. The geotechnical parameters determined
on the basis of in situ tests and laboratory tests were used in the stability analysis and the consolidation
prediction. The calculations were carried out using the GeoSlope and Plaxis numerical programs, determining
the safe heights of the individual stages of the embankment construction and the time needed to consolidate the
organic subsoil. The results of the numerical analysis indicated zones of settlement nonuniformity that require
additional strengthening of the embankment. The significant variation of the organic soil properties and the
different location of the designed embankment in relation to the existing one indicates the necessity of control
measurements of vertical and horizontal displacements as well as pore water pressures in organic subsoil.