Re-orientation of principal stresses during tunnel excavation: Model development and support strategy.

The safety and stability during the excavation and production of the tunnel is a key issue that must be addressed in tunneling engineering, which is pronounced under principal stress re-orientation. A mechanical model is therefore developed to determine the boundary curve of the failure zone of a supported circular tunnel under rotating the principal stress direction. Meanwhile, the effects of various environmental factors on the pattern of the failure zone are quantitatively analyzed. Subsequently, two critical morphological indexes are determined to elucidate the uniformity of the failure zone and the functional relationship between these two morphological indices and the environmental factors, respectively. Furthermore, technical approaches and control measures for maintaining the surrounding rock are put forward. In particular, the "long and short" coordinated hierarchical support technology has been recommended and is validated through a comparison of the designed schemes and several engineering cases. The results indicate that the proposed support technology resulted in a gradual reduction of the "butterfly wings" pattern and a more consistent failure zone in the surrounding rock. These findings are useful to ensure the overall stability and anti-interference performance of the surrounding rock of a tunnel under the complicated stress field, especially with regards to the deflection of principal stress. [ABSTRACT FROM AUTHOR]