Microstructural changes in remoulded specimens due to suction pressure

This paper presents an issue of microstructural changes in clay soils during the water loss due to increase of suction pressure. The change of microstructure affects the geological engineering properties of soils causes problems with the foundation of buildings. The volumetric changes of cohesive soils, containing significant amounts of clay minerals from the smectite group, are caused by a variable water content in soil. The phenomenon of the moisture change significantly alters the geological engineering properties of these soils as a result of shrinking and swelling. This paper aims at presenting the microstructural changes in remoulded specimens of Neogene clays caused by loss of moisture due to suction pressure. The scientific examination involved quantitative analyses of the microstructure using scanning electron microscopy (SEM) to study pore space details of remoulded specimens. Tested samples from selected levels of the Neogene clays (Poznan Series) were collected from the Warsaw-Stegny area. Samples were taken from a research polygon for these clay soils. The basic geological engineering properties of clay soils and remoulded specimens have been examined after being prepared according to strictly defined procedures. Through successive stages of the suction pressure (from 50 to 1600 kPa), the samples underwent the process of loss of moisture. Application of a novel method of sample preparation procedure for remoulded specimens allowed examining structurally homogeneous soils and obtaining results without an effect of material anisotropy. The qualitative and quantitative analysis of soil microstructures were performed using SEM and STIMAN software for quantitative images processing. The analysis allowed determination of the number of geometric and morphometric parameters of the microstructure with high accuracy. Based on this study, significant qualitative and quantitative changes in loss of moisture due to suction pressure in the process of remoulded specimens were noted along with changes in the microstructure and pore space of clay soils. The obtained results showed the effect of successive stages of "closing" of the structure of cohesive soils. Microstructural changes have a significant influence on the values of clay soil properties during the shrinkage and swelling process, which are caused by changes in the water content