GEOPHYSICAL STUDIES AND STRENGTHENING A LAYERED AND WATER-SATURATED SOIL MASS IN THE KYIV METRO CONDITIONS

Abstract

Purpose. An urgent issue for shallow underground tunnels in difficult engineering and geological conditions is the determination of the physical and mechanical properties of soils not only during engineering surveys, but also when they are studied using geophysical methods for studying ground conditions. In addition, it is important to choose ways to improve the properties of soils by strengthening, especially in areas where their strength characteristics are reduced. This ensures the efficient operation of tunnels with the elimination of hazardous phenomena such as vibration creep of soils and deformations of the track and lining. Methodology. Using the existing provisions on geophysical research, in order to identify the weaknesses of the layered and water-saturated massif and justify ways to strengthen it, the basics of a comprehensive study and production implementation have been developed to increase the level of safe operation of metro tunnels. Findings. Geophysical studies were carried out to identify weaknesses in the soil stratum along the route of the running tunnels of the Syretsko-Pechersk line of the Kyiv metro (the left bank of the Dnipro) and it was established that in present conditions, to strengthen weak water-saturated and layered soils, it is necessary to use methods of mixing soils with binders that are injected under pressure. Originality. Based on the performed analytical studies, the dependence of the porosity of weak water-saturated soils on the ratio of the acceleration of vibrations to the acceleration of gravity at certain frequencies of the path vibration caused by the movement of metro trains was obtained, and the parameters of soil strengthening on the sides and the bottom of the rim of the running tunnels were determined. Practical value. The use of geophysical methods for determining weak spots in the soil massif allowed them to be strengthened in the existing shallow underground tunnels and reduce the risk of their dangerous operation.