Properties of excavation damaged zone under blasting load in deep tunnels

The excavation loads during blasting of deep tunnels are very complex; and it may have important influence on the development of excavation damage zone. Using PFC(particle flow code), the characteristics of surrounding rock damage zone induced by blasting load and in-situ stress transient unloading respectively under different in-situ stress conditions are discussed; and through the blasting excavation damage zone detection data of the Jinping. diversion tunnel, the results of numerical simulation are verified. Researches show that the degree and range of surrounding rock damage zone induced by blasting load or in-situ stress transient unloading will increase significantly with the increase of in-situ stress degree; the damage zone will mainly appear in the area of stress concentration as the lateral pressure coefficient increased under the conditions of blasting load, the surrounding rock failure induced by in-situ stress transient unloading is mainly composed of tensile failure, the surface damage zone will uniformly distribute on excavation face; the depth of surrounding rock damage zone induced by blasting load and in-situ stress transient unload respectively under the same in-situ stress are all significantly less than the measured values, which in agreement with the measured values when considering the coupling effect of the two load. It is shown that this two kinds of loads are the main components of blasting excavation load under high stress conditions; but the surrounding rock damage zone induced loads by the coupling action of this two kinds of loads is bigger than the linear superposition of their separate effects.