Undrained Cavity-Contraction Analysis for Prediction of Soil Behavior around Tunnels

The cavity-contraction method has been used for decades for the design of tunneling and prediction of ground settlement by modeling the cavity-unloading process from an in situ stress state. Analytical solutions of undrained cavity contraction in a unified state-parameter model for clay and sand (CASM) are developed in this paper to predict soil behavior around tunnels. The overall behavior of clay and sand under both drained and undrained loading conditions could be properly captured by CASM, and the large-strain and effective-stress analyses of cavity contraction provide the distributions of stress/strain within the elastic, plastic, and critical-state regions around a tunnel. The effects of ground condition and soil model parameters are investigated from the results of stress paths and cavity-contraction curves. Comparisons of the ground-reaction curve and the excess pore pressure are also provided between the predicted and measured behavior of tunneling by using data of centrifuge tunnel tests in clay.