Overconsolidation and microstructures in Neogene clays from the Warsaw area

Abstract

The main objective of the study was determine the loading history and establish the current state of consolidation of Neogene clays, to study their lithological and microstructural properties, and to define their geological-engineering properties. To accomplish this task, series of laboratory and field tests were performed. The tests were made on clays taken from pits excavated for underground stations and tunnels (A-14-A-15) in Warsaw and from 2 borehole cores taken from the Stegny experimental field. The tests showed that: the clays are historically overconsolidated with an OCR ratio of 25-50 and their current state of preconsolidation is OCR = 2-14; their range of clay microstructures, observed for the first time, are matrix-turbulent and turbulent-laminar and there was a clear anisotropy of quantitative parameters of the pore paces, these parameters varying with depth. The engineering-geological characteristics (physical and mechanical properties) of the clays were assessed. The results of the study can be used directly to evaluate the Neogene clays of the Warsaw area for their suitability as a subsoil for engineering projects and indirectly to accomplish the same with other overconsolidated soils, particularly in regard to the study methodologies applied and described.