Excavation damage zone depth and influence factors of brittle rock

The stress-induced excavation damage occupies the main position in brittle rock mass of underground engineering. Based on the excavation damage database of underground opening, the empirical formula for damage depth of hard rock put forward by Kaiser is revised. By considering the effect of the initial stress ratio, the revised empirical formula is improved with a certain extent in the goodness of fitting and prediction accuracy. For further studies on excavation damage zone and its influencing factors, the crack initial criterion (CIC) is put forward as the mechanical index for damage zone. It is found that the damage depth assessed by CIC is coincident with the predicted values by the empirical formula and filed measured values, indicating that CIC as the index for damage zone has good feasibility. On the basis of CIC, the induced stress and damage range of the surrounding rock are analyzed under different opening shapes and orientations. It is shown that the "Harmonious hole" is not the most reasonable shape under high stress field. By setting a small radius of curvature in the minor principal stress direction, the high compression stress can be limited within a local scope, and thus a wide range of surrounding rock damage of underground engineering can be avoided. The related understanding and conclusions are of certain theoretical and engineering significance.