Abstract
This short technical note investigates the stability of a plane strain square tunnel in homogeneous undrained clay using shear strength reduction technique. The finite difference program FLAC is used to determine the factor of safety for unsupported square tunnels where an automatic generation of program script is developed using FISH programming. This developed procedure enables parametric studies to be conducted in an effective way with great efficiency. Numerical results, expressed in term of factor of safety, are compared with published classical upper and lower bound limit solutions. The comparison between these two numerical methods finds a very good agreement and the confidence level of the current FLAC model has increased significantly. With the success of model validations, a number of stability design charts for square tunnels using dimensionless ratios are presented for practical scenarios in a similar way to Taylor's slope stability charts. Examples are illustrated to show the potential usefulness of the produced design charts for practicing engineers.