Time-dependent response of tunnels considering creep effect

A viscoelastic analysis using the hyperbolic and power creep laws is developed for prediction of time-dependent closure of circular tunnels. Effect of support types and installation location in accordance with the convergence confinement method are incorporated in the analysis. The hyperbolic creep law is found to be more practical for simulation of closure response of squeezing ground than the power creep law because it is capable of modeling ground yielding around the tunnel when value of Rf close to 1.0 is used. A parametric study is performed using the hyperbolic law and the results are discussed. Predicted tunnel closure was compared with the monitoring data from a number of tunnels and they were found in good agreement. It is found that the closure and support yielding time are most sensitive to the hyperbolic parameter EuI(σ1-σ3)f and creep parameter λ. The values of Eu I(σ1-σ3)f of 200-250 and λ of 0.03-0.15 are found to be reasonable for most ground that exhibit squeezing. The analysis is useful in predicting time-dependent closure and support load for tunnels in both rocks and soils. © 2007 ASCE.