Theoretical and numerical analyses of squeezing rock mass around a spherical opening considering the existence of a damaged zone

If an underground opening is excavated using drill and blast method, an excavation damaged zone (EDZ) will appear around the opening in which its mechanical and creep properties can be very different from the initial rock mass. The existence of such a zone in squeezing rock masses can lead the time-dependent displacements to increase. Therefore, in this paper, a closed-formed analytical solution is proposed to determine the long-term performance of a spherical opening surrounded by an EDZ. To consider the time-dependent behavior, the viscoelastic Burgers model is assigned to the rock mass. After verifying the proposed method, a parametric study is performed and the influence of various factors such as the radii of the opening and EDZ, the shear modulus, and the viscosity of rock mass are investigated. It was found that if the EDZ radius is considered constant, the displacement of the cavity with 7 meters radius, immediately and after 10 years, is respectively 1.42 and 1.57 times greater than the case in which the cavity radius is 4.57 meters. On the other hand, if the cavity radius is equal to 4.57 meters, immediately and after 10 years, the displacement of the cavity wall in which the EDZ radius is 8 meters is respectively 50% and 70% greater than the case in which this radius is equal to 6 meters. When the radii of the cavity and the EDZ are constant, if the Kelvin viscosity becomes one-twentieth, the cavity displacement increases by 115% and 173% after 1 year, respectively.