Tunnel excavation makes the in-situ stress to be in unbalance state with damage area formed in strata.The releasing zone is one of the most critical parameters to evaluate the stability of Bolt-support system.Based on the comprehensive investigation on characteristics of regional geology or seismic and excavation techniques,ultrasonic wave monitor is applied to indicate rock-mass micro-fractures and damages.Based on the measured data,the rationality of bolt support is proved,and the results also provide som...