Evaluation of the safety factors of shotcrete linings during the creep stage

Abstract

Sprayed concrete linings (SCLs) used in tunnels generally develop secondary deformations over time, even in the presence of constant stress levels within the lining. These deformations influence the loading process on the lining and therefore also the stress levels within the support structure. The behaviour of a SCL in a tunnel was investigated under different operating conditions in order to evaluate the effect of secondary deformations on the evolution of stability conditions (safety margins with respect to the possible concrete failure) over time, after completion of the tunnel construction. A parametric analysis was performed to study eight different types of tunnels, with variable geometry and rock quality, and eight different types of sprayed concrete. The 64 cases of the parametric analysis covered the vast range of variability of influential parameters and yielded useful information concerning the effects of secondary deformations over time on the static behaviour of the lining and on the safety factor with reference to the possible failure of the sprayed concrete.