It is a widely accepted opinion in the tunnelling community that the primary stress state influences the cutting process, however basically no rigorous analysis regarding these effects has been conducted. In order to better understand these effects, the work has been separated in the following steps:
• A 3D numerical analysis of the secondary stress state in the rock mass while the advance approaches a fault zone, thus causing a stress increase in the face area of the competent pillar;
• 3D numerical analysis of the cutting process on heterogeneous numerical models with brittle softening behavior, with various stress states as determined from the overall 3D analysis.
The results allow definite qualitative statements about the influence of the stress state
As the TBM performance prediction is used to make reliable cost and price estimates as well as to characterize the ground conditions, special attention has been given to this currently insufficiently explored issue. Therefore, the influence of the primary stress state has to be investigated, as it is a widely accepted opinion that it has an influence on the cutting process.
In order to examine the influence of the primary stress state, the research is based on four different fields of activity:
• Numerical modelling of a TBM advance towards a fault and examination of the stresses induced at the face;
• TBM data analysis from real projects (currently pending);
• Numerical simulation of the cutting process with a highly sophisticated numerical model and examination of the influence of the stress boundary conditions on the cutting process;
• Laboratory testing of the cutting process with and without confinement stresses, in order to verify the findings of the numerical analysis.
This paper concerns only the numerical simulation of the TBM advance and estimation of the secondary stresses, and their evaluation regarding cutability.