初始地应力场对钻爆开挖过程中围岩振动的影响研究

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

采用动力有限元方法,通过分析爆破过程中开挖边界上初始地应力的高速(动态)卸载过程,研究了初始地应力场对围岩振动的影响。研究结果表明,爆破开挖过程中,在地应力较大的方向上动态卸载振动较大,因而此方向上围岩总体振动值也较大;且侧压力系数越大,影响越明显;同时,初始地应力场对爆源中远区的围岩振动值影响较近区显著,这是因为虽然在爆源近区爆炸荷载所诱发的振动比地应力动态卸载所诱发的振动大,但前者的峰值衰减速度比后者振动要快的多,故在爆源中远区,地应力卸载振动在围岩总体振动中占据主导地位。正在施工的瀑布沟水电站地下厂房处于花岗岩山体中,施工区地应力值约为20 MPa。利用小波变换突出信号奇异点的特性,并采用小波模极大值方法,识别了该地下厂房开挖过程中实测围岩振动曲线的地应力动态卸载振动到达时间;初步分离了围岩总体振动中的地应力卸载振动,对数值模拟结果进行了验证。

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.