Study On Damage Threshold Of Surrounding Rock In Tunnel Blasting Excavation

Blasting is the main method of railways, waterways, road tunnels and mine tunnel excavation. In the blasting process, except for some blasting load are used to broken rock, there are some load will cause a range of injuries in tunnels or roadway.In this paper, take Tai shan nuclear power plant water intake tunnel blasting excavation project as an example, through field tests and monitoring of blasting vibration and acoustic test, the blasting excavation process is simulated that combined with the large dynamic finite element software ANSYS / LS-DYNA,.Offered to the safety threshold that used blasting vibration velocity characterizated of water intake tunnel excavation blasting rock damage in Tai shan nuclear power plant.The rock damage theory of tunnel blasting excavation is analyzed, combined with field results that the wall rock damage of heading face is mainly initial damage that resulted by the tunnel blasting. However, in a continuous blasting, tunnel surrounding rock in the rear will be a range of cumulative damage from the demolition earthquake wave. The theory of rock damage and the propagation and attenuation discipline of blasting vibration are analyzed to demonstrates the dangers of cumulative damage of tunnel surrounding rock, and the control method that characterizated by the velocity of blasting vibration is proposed.The powerful display and analysis capabilities of LS-DYNA software are used to simulate the tunnel blasting. The curve of vibration velocity and stress-time are analyzed to got the propagation of vibration velocity and stress is a fast decay process in a short time. And when the distance at about 20 meters behind the wall rock excavation face that vibration speed is 1.39cm/s, calculated the range of tunnel contour rock damage is 1.97 m.The TC-4850 vibrometer is adopted to test and monitor field blasting vibration.Analysis the field test data and obtained the attenuation discipline of blasting vibration, the empirical formula of Sa Tao Minkowski form by regression analysis in the horizontal and vertical direction is given. The blasting vibration velocity of distance at about 20 meters is maintained at 1.5cm / s.The RSM-SY5 intelligent acoustic instrument is applied to conduct sonic wave test, got the development law of rock damage, and results show that the cumulative effect of rock damage degree is relate to the grade of blasting impact load(this paper is characterized by vibration velocity), the larger the load, the more obvious the cumulative effect, and below a certain threshold of blasting load, you can ignore their cumulative effect to the degree of rock damage. When the tunnel blasting frequency reach 20 times, each drilling depth is 1meters, that is when the blasting distance approaching 20 meters, damage accumulation tends to zero.The safety threshold of rock damage in Tai shan nuclear power plant water intake tunnel blasting excavation is proposed by combined with the previous conclusions,that is: when the tunnel blasting, the vibration velocity of particle not more than1.5cm / s at 20 m from the explosion source.