When drilling deep wells in thick ice deposits, significant difficulties arise in maintaining an open borehole due to the specific viscoplastic properties of ice. At present, there are many ways to fight wellbore swarming while drilling in ice. The most effective and reliable way is filling of boreholes with non-freezing pouring liquids, as the temperature of borehole walls in ice deposits is rather low: for example, ice temperature at Vostok Station (Antarctica) is up to minus 55-57°С at a depth of 20-50 m and minus 5-10°С at a depth of 3500 m and more. Filling fluids are usually formed on the basis of ecologically clean glycol mixtures and have density 0.95-0.96 g/cm 3 . The success of wells in such conditions depends on correct determination of necessary height of filling the well with filling fluid in order to avoid appearance of elastic deformations and ice creep contributing to wellbore contour floating and stoppage of drilling tool down the previously drilled part of the wellbore. Taking into account the equilibrium between lateral stress and pressure of the pouring fluid column, as well as the maximum deformation in the transverse direction, a dependence for the height of the pouring fluid column was obtained. The methodology was tested while drilling a deep borehole (total depth of more than 3620 m) at Vostok Station (Antarctica).
The viscous fluid flow model for estimating the stress-strain state of potassium salt in the bulk stress state at a sufficiently high level of acting stresses allows us to describe the behavior of salt massifs, in particular the process of flowing (contour convergence) of workings in the massif thickness over time. The stated solution is valid only for small displacements compared to the thickness of the rock layer. In addition, it is assumed that the layer thickness is much smaller than its transverse dimensions. In this case, the selected form of the current function gives a satisfactory agreement with the experimental data. The proposed method can be used for natural measurements of Poisson's ratio on rather thin layers of potassium salt in a volumetric stressed state with axial load exceeding 60 MPa or on targets with diameter to height ratio over 5 In this case, the behavior of potassium salt corresponds quite well to the viscous fluid model.
Field observations show that the distribution of stresses around mine workings is uneven both in transverse and longitudinal directions. To take into account this distribution of stresses, we consider the interaction of the mine support with the surrounding rock massif. The roof support is considered as an elastic long closed cylindrical shell. The load acting on the shoring changes irregularly both along the shell and in the transverse direction: p = p(x,0), where x is the distance along the generatrix expressed in fractions of the radius; 9 is the central angle expressed in radians. Then, two cases can be considered: the support is under the action of axisymmetric radial load depending only on one variable x, the support is subjected to load depending only on the angle 9 The solution of the problem for the load of the form P = p(x, 9) is obtained by summing up these two solutions. Let's estimate average loads on a roof support for typical conditions of shaft construction in the elastic mode of interaction: R 0 = 3.0; R l = 3.5 m; R - 3.25 m; h - 0.5 m; Vj = 0.25; / = 0; v - 0.25; = 2 - 10 4 MPa; £ = 2 - 10 4 MPa Thus, when modeling vertical shaft support by a closed cylindrical shell the calculated average load is three times less than the corresponding value for a flat problem.
