THE SAFETY IMPACT MONITORING ANALYSIS OF HIGHWAY TUNNEL BLASTING EXCAVATION CLOSE TO EXISTING CIVIL DEFENSE ENGINEERING

For the highway tunnel through the existing civil air defense engineering in weak surrounding rock，the smooth-surface millisecond blasting technique of small drilling depth was used，and the blasting vibration effect and its impacts decreased for reasonable arrangement of excavation sequences; combined with the construction monitoring and feedbacks in time，the blasting vibration was controlled effectively by adjusting the blasting parameters and construction process; then the safety of the civil air defense engineering was guaranteed and the highway tunnel passed safely and smoothly through the section of the existing engineering in the meanwhile． The monitoring results show that the tunnel blasting excavation scheme，construction process and blasting control measures are important factors affecting the safety of adjacent existing civil air defense engineering． In the blasting construction for the Ⅳ，Ⅴ class surrounding rock，the difference of main vibration frequency of different direction，energy spectrum distribution and amplitude is significant． The main longitudinal horizontal vibration frequency along the tunnel is in the low frequency band of 0 ～ 20 Hz，and the transversal and vertical vibrations of the main vibration frequency band are more wider ( 0 ～ 200 Hz) ． The power spectrum peak of the former is more than 10 times of the latter． In the process of monitoring，special attention should be paid to the effect of the vibration with the main vibration frequency under 20Hz and the speed greater than 50 mm/s． Changes of subsidence and stress of surrounding rock of civil air defense warehouse floor did not exceed the requirement limits of the specification．