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.
In the article the outcomes of researches of the plane (two-dimensional) strains and deformations of an array of breeds around mentro tunnel of the St.-Petersburg underground are indicated: the settlement scheme, outcomes of accounts. The reasons and mechanism of settlings of a surface and contact proterozoic clays with soils are revealed.
A dependence of Proterozoic clays in the faces of tunnels under construction from different factors affecting them, i.e. the depth of the seam, thickness of clays up to the Quaternary sediments, prognostic properties of rocks and tunnels diameter is analysed. Indexes of exposed rocks stability in different schemes of rock deformation are offered. The mentioned indexes can be recommended for underground surveying when forecasting surface deformation in underground construction works.
