The Longitudinal Deformation Profile (DP) is an important component of the Convergence- Confinement method. The present study concerns numerical simulation, by means of the finite difference code FLAX 3D, to calculate the DP curve for an unlined tunnel driven in a Burger viscoelastic rock mass model in various stress fields. Model constants of the Burger rock mass are selected according to a detailed literature review and parameterized in order to simulate different time-dependent situations of rock mass. The results are plotted, analyzed, discussed and compared against known empirical solutions and found in good agreement.
Observed displacement of a specific point in an underground excavation can be expressed as the sum of displacements caused by two effects, the face advance and the time dependent reaction of the ground. In order to describe the time-dependent deformation due to creep in tunnels, various approaches have been established based on analytical, empirical and numerical methods. To briefly report an indicative selection of researches that include time in stability analysis of tunnels, one would start with the basic research that was presented by Salem et al [12]. In their suggested analytical method an explicit solution was proposed for the determination of the radial displacements and the ground pressure acting on tunnel support. It was based on a Kelvin-Voigt theological model. A closed-form solution for the calculation of the pressure acting on tunnel support structures was given by Samurai [10]. He introduced an "equivalent initial stress" in order to solve three-dimensional effects of the tunnel face progression with a two-dimensional plane strain model of tunnel- support structures for elastic and viscoelastic media. Also, by means of a three component viscoelastic model, relations are given for the calculation of tunnel wall displacement and pressure on lining. In another research by Ghaboussi and Gilda [4], the short-term effects that develop when a tunnel is driven in a ground showing viscous behaviour associated with the devi atomic deformations is studied. Also, radial deformation of a lined tunnel when there is an unsupported zone between the face of the excavation and the liner, the effects of a temporary interruption of the excavation process and of various rates of tunnel excavation. More recently, Salami [11] performed viscoelastic analysis with the Abacus code to model ground squeezing through the heavily sheared and fault zones of the Red Pine shale of still-water tunnel (Utah, USA) under an overburden of 700 m. He concluded that the effect of tunnel face advance on the crown displacement extends to a distance of about 2 tunnel diameters behind the tunnel face and 1.5 tunnel diameters ahead of the face. This zone of influence is slightly wider than the zone that has been predicted from elastic analysis. Yiouta-Mitra et al [15] performed viscoelastic analysis of materials with swelling and creep potential to investigate the effects on the tunnel final lining loads. Sophistic numerical code and the viscoelastic Persona model were used on the basis of the convergence-confinement method.
