DEFORMATION PROPERTIES OF MIOCENE CLAYS IN THE OUTSKIRTS OF LVIV (AS BASED ON THE INDICATORS OF SWELLING AND SHRINKAGE)

Abstract

The results of experimental studies of the composition, physical properties and processes of swelling and shrinkage of Kosiv clays in the outskirts of Lviv are considered. The clays of the Kosiv suit occupy large areas in the Lviv city. They extend in the form of an almost continuous cover 3–5 km wide from the southeast of Zelena-street to the northwest of the village Riasna-Ruska. The total area occupied by clays exceeds 50 km2. The clay layer is covered by an almost continuous mantle with a thickness of 6– 10 m of degraded loess and other genetic types of sediments and is below the groundwater level, so their natural humidity does not change for a long time. The thickness of clays varies from 1–3 to 20–25 m. In some areas, in particular within the Lewandiwsky ledge of the Lviv plateau (Subotivska, Olesnytskoho, Syayvo streets, etc.), on the south-western outskirts of the plateau (Obroshyno village) and on the south-eastern slopes of Roztocze (Kleparivska street in Lviv, village of Vidnyky) they lie directly under the soil-vegetative layer or lowpower layer of man-made soil, in the aeration zone, directly are the subsoil of the foundations and have the ability to swell and shrink. Studies have shown that the mineralogical composition of the clay component contains 18.6 % montmorillonite, 35.1 % quartz, 17.5 % hydromica and 28.8 % feldspar. The particle size distribution of the soil is dominated by parts smaller than 0.01 mm. Clays have a firm consistency, low natural humidity and density. With additional moisture, they swell, and when moisture is lost, they shrink. The absolute value of the index of free-swell (εsw) of the soil when it is moistened reaches 0.058, which gives reason to classify the soil as weakly swollen. The value of the swelling pressure is on average 0.48 MPa. The maximum linear shrinkage is 11 %, and volumetric – 18 %. The obtained data show that the Miocene clays (Kosiv suit) of the outskirts of Lviv are characterized by the ability to swell and shrink when their humidity changes and require detailed engineering and geological studies and a number of special measures to ensure the stability of buildings and constructions.