Thrust force requirements for TBMs in squeezing ground

Rapidly converging ground may exert such a high pressure on the shield that the thrust force is no longer sufficient to overcome shield skin friction and the TBM becomes jammed. This paper advances a number of theory-based decision aids, which will support rapid, initial assessments to be made of thrust force requirements. A comprehensive parametric study has been carried out using the finite element method and, based on the numerical results, dimensionless design nomograms have been worked out that cover the relevant range of material constants, in situ stress and TBM characteristics. The nomograms make it possible to assess the feasibility of a TBM drive in a given geotechnical situation and to evaluate potential design measures or operational measures such as reductions in shield length, the installation of a higher thrust force, increases in the overcut or the lubrication of the shield surface, thus making a valuable contribution to the decision-making process.