Safety Threshold Determination for Blasting Vibration of the Lining in Existing Tunnels under Adjacent Tunnel Blasting

Abstract

The effects of tunnel blast excavation on the lining structures of adjacent tunnels are comprehensively studied for the Xinling highway tunnel project. First, the LS-DYNA software is applied to obtain the characteristics of vibration velocities and dynamic stressesatdifferentpositionsofthetunnelliner.Theresultsindicatethatthemaximumpeakparticlevelocity(PPV)islocatedon the haunch of the lining facing the blasting source and that the PPV and peak tensile stress decrease with the increase in the surroundingrockgrade.Second,asitetestonblastingvibrationisconductedtoverifythesimulationresults.Byusingregression analysisofthemeasuredvibrationdata,thecalculationmethodofmaximumchargeperdelayforoptimizingblastingexcavation under different surrounding rock grades is obtained. Finally, based on the statistical relationship between crack alteration and PPVontheliningbeforeandafterblasting,thesafetythresholdsofPPVfordifferentportionsofthetunnelaredetermined.The recommended safety threshold of PPV is 10cm/s for intact lining and for B-grade and V-grade linings of the surrounding rock tunnel. However, if the lining crack grade falls between 1A and B, then the recommended safety thresholds of PPV for the IIIgrade and IV-grade surrounding rock tunnel are 5cm/s and 6cm/s, respectively. The threshold PPV proposed in this study has been successfully applied to restrict blast-induced damage during new tunnel excavation of the Xinling tunnel project.