ENGINEERING-GEOLOGICAL PROPERTIES OF THE KOSIV FORMATION CLAYS IN THE LVIV AREA AND THEIR ENVIRONMENTAL ROLE

Abstract

The clays of the Kosiv Formation (suite) cover a large area within the city. They form an almost continuous cover 3–5 km wide, extending from the southeastern area near Zelena Street to the northwestern outskirts toward the Ryasne-Ruska village.The total area occupied by these clays exceeds 50 km².The clays generally occur at depths of 6–10 m below the ground surface and only locally lie directly beneath the soil-vegetation layer or technogenic deposits.The thickness of the clay deposits varies from 1–3 m to 20–25 m.The clayey strata overlie the gypsum–anhydrite deposits of the Tyras Formation; in areas of their erosion, they overlie on sands, sandstones, and limestones of the Lower Badenian, and more rarely – on marls of the Upper Cretaceous. The main part of the studied stratum is composed of cloddy, occasionally argillite-like, hard to semi-hard, rarely medium plastic carbonate clays.The principal clay minerals are montmorillonite, accompanied by minor amounts of kaolinite and hydro-mica. Significant amounts of glauconite are present in the silty, silty–sandy, and silty–sandy–gravelly facies. The extremely high heterogeneity of the lithological and mineralogical composition determines a wide range of variations in the engineeringgeological properties of the clays.Thus, the natural moisture content of the clays varies from 13 to 99%, the plasticity index – from 0.03 to 1.09, the density of the natural soil – from 1.40 to 2.08 g/cm³, the porosity coefficient – from 0.47 to 2.71, and the degree of pore saturation – from 0.54 to 100%. Clays with a low degree of pore saturation exhibit swelling behavior. The soil exhibits an absolute free swelling index (Eₛw) of up to 0.058 upon wetting, with an average swelling pressure of 0.48 MPa.The maximum linear shrinkage of the clays is 11%, while the volumetric shrinkage reaches 18%.The clays exhibit a deformation modulus ranging from 3 to 34 MPa.The clays exhibit internal friction angles of 10–30° and cohesion values ranging from 18 to 96 КPa.The low strength of the clays is a major factor in landslide formation. The filtration coefficient of sandy varieties ranges from 0.005 to 0.01 m/day, whereas that of highly plastic clays ranges from 1×10⁻⁴ to 1×10⁻⁵ m/day, thereby forming a protective barrier against anthropogenic contamination of the underlying aquifers and slowing the development of karst processes.