Abstract: The dynamic unloading effect should be considered when tunnel or cavern is excavated by drilling and blasting method under high in-situ stress; and its damage zone forms will eventually be affected by multiple factors. By using three-dimensional finite difference software FLAC3D, the distribution of surrounding rock damage zone induced by the coupling effect of blasting load and dynamic unloading is discussed; then the influences of lateral pressure coefficient, the mechanical properties of rock mass and the unloading rate on damage range of surrounding rock are taken into account in the analyses; and finally through the excavation damage zone detection data of Meihuashan Tunnel of Gan-Long Railway in Jiangxi province. The results of numerical simulation are verified. Researches show that the rock damage zone under the coupling effect of blasting load and dynamic unloading is significantly greater than that only considering the blasting load; dynamic unloading of in-situ stress can not be ignored. As the lateral pressure coefficient increases gradually, the damaged zone presents the obvious directivity, when the lateral pressure coefficient is 1, the damaged zone will uniformly distributed along the excavation contour surface, and when the lateral pressure coefficient is not 1, the damage zone will mainly concentrate in minimum principal stress direction. The better rock mechanical properties is, the smaller the damage zone will be. The faster the unloading rate, the larger the damage zone of surrounding rock will be; but the impact is not significant. The results provide suggestions for stability analysis of tunnels under high in-situ stress and supporting design of the cracked surrounding rock.

Key words: rock mechanics, surrounding rock damage, blast, high in-situ stress