The changes of permeability coefficient in the stage consolidation process of gyttja and lacustrine chalk : the methodology of valuation

Lacustrine deposits, e.g. gyttja and lcustrine chalk, in natural conditions are weak soils from the engineering point of view. These soils under loading have large and long-lasting consolidation settlement. In the last years, these soils have been more often used as a subsoil, mainly for road and hydraulic engineering embankments. To predict the settlement, we have to know the strain and filtration parameters of the subsoil. The paper presents the results of coefficient permeability tests of gyttja and lacustrine chalk, performed in oedometer tests after following loading steps. The results have allowed obtaining downward but various trends of coefficient permeability changes in the consolidation process due to a decrease of void ratio. In general, the differences of trends are related to different types of gyttja. In the case of mineral-organic high-carbonate gyttja, three different decreasing trends were obtained. For these different trends, the causal relation was determined to the lithological impact factor. The lithological impact factor in the paper is proposed as the combination of main lithological characteristics