Effect Mechanism of Excavation Blasting in an UnderCross Tunnel on Airport Runway

摘要

Blasting excavation in a tunnel passing beneath an airport is quite rare at home and abroad.In this paper,the blasting excavation for the construction of a four-arc double-track tunnel passing beneath Xujiaping Airport in Enshi is introduced and in-site tests are carried out to monitor the vibration in airport runway.Field monitoring data indicated that,throughout the tunneling operation,frequencies between runway's self-vibration and blasting vibration differed appreciably,and no resonance would be caused.In terms of the influence mechanism,the dynamic finite element program LS-DYNA was adopted,whose reliability was verified by field monitoring data.The numerical results showed that the airport runway was affected little and an existed cave could amplify the amplitude of blasting vibration to an extent.Meanwhile,based on the stress wave theory and the failure law of maximum tensile stress,the safety threshold for the runway induced by blasting vibration was obtained.Then the safety threshold of PPVwas also decided through the statistic relationship between the peak value of tensile stresses and the PPV on the runway.As the safety thresholds derived from both fore mentioned methods was compared,with Safety Regulations for Blasting in China (GB 6722-2011) taken into account,a final safety threshold was decided.