The factors and possible consequences of regional changes in engineering and geotechnical status of loesses and loessy-loamy soils of Ukraine

Abstract

Over the recent decades in Ukraine regional activation of flooding of lands, accompanied by landslide formation and subsidence of surfaces take place. It is caused by interaction of a complex of natural and technogenic factors (global climate changes, groundwater afflux in areas of impact of reservoirs, flooding of numerous mines and quarries, etc.). On the territories of the most widespread in Ukraine loessy and loessy-loamy soils these phenomena become the most dangerous transformations of engineering and geotechnical state of the upper part of the geological environment. The researches carried out at the ITGIS have clarified that the specific engineering and geological properties of loessy soils (soaking, subsidence and thixotropy) are the main factors contributing to progressive reduction of engineering seismogeological stability of these soils. The cause of thixotropic dilution is the operation of various vibration mechanisms or closeness of the objects causing vibration (railways, etc.). Thixotropic dilution is mostly caused by vibrational destruction of non-waterproof aggregate structure of loessy soil. Destruction is also accompanied by vibrational movement of products of destruction into the pore space. After termination of vibration the aggregate structure is partially restored due to the formation of secondary aggregates.
Today more than 50% of 460 cities and 885 urban-type settlements in Ukraine are located in the zone of subsiding loessy and loessy-loamy soils, up to 15% are affected by natural and technogenic karst formation, and in 9% (123) of the cases development of landslides was recorded. Natural and technogenic flooding of the territory was recorded in more than 40% (546) of cities and towns. Therefore, there are complex changes in the geotechnical conditions in majority of the industrial urban agglomerations of Ukraine and deterioration of ecological and geological parameters of life within them. The zoning by the regional geotechnical risk of flooding of cities and villages of Ukraine situated on loessy and loessy-loamy soils should be carried out on the basis of the combined effect of natural and technogenic factors. It is recommended to apply the additive model of influence on geotechnical risk. The mentioned risk is proposed to be quantified by indicators of the specific density of areas of flood and landslide development in both technogenic and natural conditions.
The property of water-saturated loessy soils to move to the quicksand state is mostly due to the structural features of these soils and to the laws of their transition to the rarefied state. The process of obtaining by loesses (in circumstances of long-term flooding) of fluid-thixotropic properties develops in the Southern region on irrigated lands and begins to spread to the other regions. It is necessary to continue scientific and production works to improve the methodological basis of an assessment of the impact of modern changes in levels and chemical composition of groundwater, negative technogenic effects on the subsoil, global climate change and other factors on formation of the geotechnical risk using modern technologies of GIS and Earth remote sensing, as well as to complement this basis with ecologic, economic and insurance assessments of the risk of life safety.