Characteristics Of The Vibration Of Surrounding Rock During Tunnel Excavation Blasting

Much attention is paid on the development and utilization of hydropower due to its green and clean features.Hydropower construction involves many tunnel blasting excavations.The blasting-induced vibration of surrounding rock and its influence have been one of the key issues in geotechnical engineering.A comprehensive analysis of vibration characteristics of surrounding rock induced by excavation blasting in tunnel will be a great help in optimizing design of tunnel rock mass blasting excavation,improving the process of blasting excavation and controlling engineering disasters.In this paper,the vibration induced by excavation unloading only,the coupling of blasting load and transient release of in-situ stress,and air overpressure are all studied through theoretical and numerical simulations.Some main research results are concluded as follows.(1)Based on the theory of transient unloading and the measured blasting vibration data of the tail tunnel No.1 of Pubugou hydropower station,mechanism and characteristics of surrounding rock vibration induced by in-situ stress unloading was studied.The results reveal that a large additional dynamic stress produced during blasting when stress on the excavation surface transient unloaded,which could cause a seismic wave.And vibration of the surrounding rock was caused when the seismic wave propagated through.It’s proved the vibration induced by excavation unloading has a low frequency and distributed in the obvious lower frequency band compared with the blasting load induced vibration.The peak value of the vibration is smaller than that of the explosive load in the vicinity of the excavation surface,but nearly the same at the far distance,increasing with the increase of the In-situ stress and the excavation surface area.(2)Based on the Lagrangian erosion algorithm,the propagation processes of rock burst under different ground stress are studied through numerical simulation.The vibration characteristics of the surrounding rock induced by the coupling of the blasting load and the in-situ tress unloading are studied.The results show that under low ground stress,the blasting vibration is mainly induced by the blasting load,the vibration duration is short and the peak value is small.Under the high ground stress,the vibration duration is longer,the vibration signal mutation is more frequent and the peak value increases with the ground stress level.All the vibration power spectral density curves show two obvious advantage frequency band,the energy distribution proportion of the lower band increses with increasing the in-situ stress.An increase of the lateral pressure coefficient significantly increases the peak patical vibration velocity(PP V)in the direction of ground stress increasing.And the coupling effect of the geostress unloading increases the duration and increases the peak value of the vibration,as well as the low frequency part of the vibration.(3)On the basis of monitoring in the blasting test of Feng-ning Pumped Storage Power Station,the air overpressure-induced vibration of surrounding rock during tunnel blasting excavation was studied through theoretical and numerical simulation.Air overpressure generated during blasting excavation in narrow-bore tunnel was large enough to cause the vibration of surrounding rock,which was characterized by high PPV,long duration,and slow attenuation.The arrival time of air overpressure-induced vibration was determined by the propagating velocity of air shock wave.There were two kinds of air overpressure induced vibration at a certain point,the first was the arrival of the air overpressure-induced vibration acting on the surrounding rock of front tunnel,the later was caused by the air overpressure direct acting on the measurement point.The vibration waveform recorded in site experiment was mainly air overpressure-induced vibration by directly acting on the tunnel surrounding rock.