STUDY ON IMPACTION OF INITIAL GEOSTRESS FIELD ON VIBRATION OF SURROUNDING ROCK DURING EXCAVATION WITH DRILLING AND BLASTING METHOD

Using the dynamic finite element method,the impaction of initial geostress on the vibration of surrounding rock(VSR) in the process of blasting-excavation is studied by analyzing the dynamic unloading of in-situ stress on the excavation boundary.It is found that the vibration induced by the dynamic unloading of in-situ stress(VIDU) at the maximum principal geostress direction is larger than the one at the minimum principal geostress direction.The larger the VSR is,the larger coefficient of lateral surrounding rock pressure is.The influence of initial geostress on the VSR in the middle and far fields away from the explosion source is much greater than that at the near field.Though the vibration induced by blasting load is larger than the VIDU in near field of the explosion source,the former attenuates much more quickly than the latter.So in middle and far field,the VIDU plays the leading role in the total vibration of surrounding rock(TVSR).The vibration induced by excavation of the underground powerhouse with drilling and blasting method at Pubugou Hydropower Project is presented as an example of the transient unloading of in-situ stress of rock mass,where the rock is granite with an initial geostress about 20.0 MPa.The arriving period of the VIDU in the measured vibration curves is identified employing the maximum module method of wavelet transform,which has the characteristics of identifying the abrupt change of signal.The VIDU is separated from the total vibration to a certain extent;and then the numerical simulation results are verified.