Thermo-chemo-mechanical assessment of support effectiveness during tunneling in squeezing conditions

Recently, the combination of shotcrete as the primary lining and of face reinforcement by means of fiber-glass dowels was successfully employed during tunnel excavation in squeezing conditions (e.g., in soft rocks under high overburden stress). In this paper, numerical results obtained from axisymmetric analyses considering the application of the shotcrete lining and the installation of fiber-glass dowels at the tunnel face are presented. In order to account for time-dependent processes in the ground, a viscoplastic material model was chosen. For the description of the mechanical behavior of shotcrete, a thermo-chemo-mechanical approach is employed. The obtained results provide insight into the ground-shotcrete interaction, the effect of face reinforcement by means of fiber-glass dowels, and the state of stress in the shotcrete lining. Moreover, the variation of ground properties allows evaluation of the loading and effectiveness of the employed support means for different geotechnical conditions.