SELECTED GEOTECHNICAL PROBLEMS OF EXPANSIVE CLAYS IN THE AREA OF POLAND

In Central European conditions, each building stratum in its surface zone is exposed to the impact of numerous diverse anthropogenic and natural factors. Expansive clays are soils that are very special as regards the impact of external factors. From an engineering point of view, the occurrence of the substratum shrinkage phase after the swelling phase is the most dangerous for constructions. Expansive clays are typical for nearly half of Poland area. These are tertiary mio-Pliocene clays of the Poznan series. Characteristic symptoms of buildings damage due to the base expansiveness include: expanding cracks of bearing walls from the foundation upwards, cracked lintels, distorted windows, etc. The Poznan series clays are characterised by expansive properties that are high cohesiveness (strength) and a low compressibility is a feature of an expansive substratum in a natural condition. The leading idea of the paper is to present to practitioners some selected results of the studies on the nature of these soils, generally considered to be good from a civil engineering point of view but, at the same time, dangerous for those who ignore their genetically shaped geotechnical properties.