Abstract：The viewpoint that the process of the initial stress unloading in rock mass during blasting is a dynamic process is brought forward，and the theory of stress wave and propagation is employed to analyze the movement process of the rock block under the sudden unloading of the initial stress during rock excavation by blasting. The results show that，under the condition of sudden unloading of initial stress，a rigid body displacement could occur，besides an elastically reverting displacement，which will lead to the opening of the jointed rock faces and the loosing of the rock mass. If the initial stress is high enough，the induced horizontal displacement of rigid body will be much larger than the elastically reverting displacement. The calculated results also show that the opening displacement of the jointed rock face is approximately proportional to the square of the value of the initial stress. The process of the dynamic unloading of the initial stress can be employed to explain the mechanism of the loosing of jointed rock mass during rock excavation by blasting.
