Characterization and engineering properties of AMU Morasko soft clay

AMU Morasko soft clay is the normally consolidated, postglacial clayey silty sand to sandy clay, deposited during the last glaciation (Weichselian) within the marginal zone of end moraine of Posnanian Phase. These soils are characterized by low plasticity, high porosity and are fully saturated, therefore, from a geotechnical point of view they can be defined as soft clays. The over 10 meter thick complex of clayey glacial sediments is covered with fine and medium sands with single grains of gravel of the so-called first sandur level from the youngest glaciation. This kind of sediments are very common in the area of north-western Poland and, due to high compressibility, become a problematic subsoil for the shallow foundations. The high porosity and saturation also causes significant problems in obtaining high quality samples for laboratory tests. This means that in situ tests are very often the only possible and economically justifiable test methods. Extended investigations carried out on these clays, which provide reliable correlations between in situ and laboratory test results, will be very useful. For the purpose of this research paper, a wide variety of in situ (CPTU, DMT, FVT) and laboratory (physical properties, direct shear, oedometer) tests have been carried out on the material found at the depth of up to 16 m, in the area of 8 ha, within the campus of Adam Mickiewicz University (AMU) in Poznan, Poland. Preliminary investigations (performed four years ago) showed high uniformity of the test site. The current laboratory tests were carried out on both high quality natural samples and reconstructed samples. The rate effect on the results of some of the tests was also investigated. The obtained results allowed to present a wide geological and engineering characterization of these interesting glacial deposits.