Activity laws of microseisms and rockbursts in deep tunnels by TBM tunneling

For the deep tunnel of JinpingⅡ Hydropower Station excavated by TBM, based on the seismic monitoring data and rockbursts, the temporal and spatial distribution characteristics of microseismic events and rockbursts and evolution laws of microseismicity information during the preparation process of rockbursts are studied. The conclusions are drawn as follows: (1) The active period of microseisms and the peak period of rockbursts are the working time and within one hour after stopping working for TBM. The microseismic activity mainly ranges from 3 times the tunnel diameter behind working face to 0.4 times ahead, and its peak value is located at 0.8 times the tunnel diameter behind working face. The rockbursts mainly occur within the region 2 times the tunnel diameter behind working face, especially the high-risk zone of rockbursts lies in the region as large as 1 times the tunnel diameter behind working face. Therefore, there is certain space-time relativity between the microseisms and the rockbursts. (2) A sudden increase of microseismic released energy or the steep rise of cumulated apparent volume (CAV) with a sharp drop of Schmidt number in the time sequence is an microseismic anomaly, which is a premonition of rockbursts. (3) The spatial distribution pattern of mircroseismic events shows a transformation from random to clump distribution in certain zone with time, and the degree of their clump dispersion pattern gradually increases, simultaneously accompanied by a growing number of microseismic events with large magnitude and high energy, that is, it is an microseismic anomaly and also a premonition of rockbursts.