Influence of thickness of Proterozoic clays in the tunnel roof on shifts of clay-sediment contact

Abstract

The study of the stress-strain state of the rock massif during the driving tunnels in the layered environment is a rather complicated geomechanical problem. The paper reflects the results of the investigation of the planar (two-dimensional) stress-strain state of the rock massif around the St. Petersburg Metro tunnel by the finite element method. The data of tests of physical and mechanical properties of Proterozoic clays carried out in different years by different organizations are summarized. The calculation scheme representing a two-layer plate of 80 x 80 m with a 6-m diameter tunnel excavated at the depth of 60 m from the surface in Proterozoic clays covered with the thickness of the Quaternary deposits of variable thickness is presented. The causes and mechanism of deformation of the rock strata, subsidence of the contact of Quaternary sediments with sediments and, as a consequence, the day surface are revealed. Results of calculations, values of tunnel contour subsidence, subsidence of clay-sediment contact at 5 and 20 m ceiling, subsidence of day surface, confirmed the assumption made earlier that the deformation of the covering strata is significantly affected by the thickness of clay in the tunnel roof.