Abstract: In order to forecast and evaluate the large squeezing deformation of surrounding rock tunnelling by TBM, the mechanical properties of large squeezing deformation has been analyzed. And large squeezing deformation is defined as a kind of deformation in which deforming speed is high, and the amount of the deformation is large and may exceed the overcut gap between the shield and the surround rock mass, with rate of convergence slow, and time dependence significant. If the ratio between surrounding rock convergence deformation and excavation radius is greater than or equal to 1%, and the ratio between convergence deformation and the overcut gap is greater than or equal to 1, large squeezing deformation will occur. And the squeezing deformation is divided by the above two indexes into five grades: no squeezing, minor squeezing, medium squeezing, severe squeezing and extremely severe squeezing.

Key words: deep ground, TBM, large squeezing deformation, deformation grade