Numerical analyses of blast wave stress propagation and damage evolution in rock masses

By means of finite element method the blast wave stress propagation and stress distribution in the wall rocks damaged by initial tunneling excavation were numerically analyzed. The damage evolution of rocks subjected to the wave stress was evaluated upon the employment of JHC constitutive model and damage variable D of rock element. It is shown that the influence of initial damage existing in wall rocks on properties of wave stress propagation, affecting domain and distribution depends on the extents of initial damage. The initially existing damage has apparently affected on wave stress propagation and stress distribution as long as its quantity exceeds a threshold value. It turns out that there exists an effective acting span Lp by which the blast wave stress influences on th initially damaged rock as long as a certain volume of explosive remains. Within this domain, the rock damage induced by blast wave stress increases with the increment of initial damage of rocks. Beyond this area scaled by Lp, the accumulated residual inelastic strains and residual tensile stresses in the damaged elements seem to be capable of balancing the compression wave stress resulted from the later explosion, and therefore, prevent the elements from being over damaged. This mechanism seems to dissipate the blast wave stress action and vibration energy. The reason for this phenomenon and mechanism was interpreted. In addition, the relationship between the effective acting span of wave stress and the initial damage in terms of equivalent stress was derived.