Abstract：The characteristics of vibration induced by dynamic unloading of in-situ stress(VIDU) on the excavation contour during blasting is studied with combined method of numerical simulation by dynamic FEM and verification with monitored in-situ vibration data. The VIDU is a superimposure of the vibration induced by dynamic unloading of radial in-situ stress(VIDUR) and shearing in-situ stress(VIDUS). It is founded that the distribution of VIDU，VIDUR and VIDUS are all determined by the distribution of unloading in-situ stress(IS) respectively. The IS depends on the coefficient of lateral surrounding rock pressure l and the comparatively width of blasting layer b. In the maximum principal geostress direction，the VIDUR and VIDUS have the same direction and the summation is VIDU. The situation is conversed at the minor principal geostress direction；the VIDUR and VIDUS have different directions and the VIDU equals the difference of them. The distribution of VIDU in the surrounding rock of circular tunnel beyond the excavating contour is ellipse-shaped；and the major axis of which is always at the direction of the maximum principal in-situ stress direction. The larger the l is，the larger the major axis of the ellipse is. The vibration induced by excavation of the underground powerhouse with method of drilling and blasting at Pubugou Hydropower Project is presented as an example of the transient unloading of in-situ stress of rock mass. The arriving moment of the VIDU in the field vibration curves is identified employing the maximum module method of wavelet transform，which has the characteristic of making the abrupt change of signal. The VIDU is separated from the total vibration to a certain extent；and the numerical simulation results are then verified.
