Measurement of Blast Damage Characteristics and Stability Analysis of Large-Span Tunnel Surrounding Rock

Abstract:

To explore the cumulative damage evolution law and stability characteristics of the surroun-ding rock during the blasting excavation of large-span tunnels, this study used a rock acoustic wave tester and pressure sensors to conduct on-site measurements of the damage characteristics of the surrounding rock and the stress of the initial support structure during the blasting excavation process. Based on the measured results of the surrounding rock damage, the numerical simulation method was used to analyze the stability of the tunnel when there is damage to the surrounding rock. The research results show that the influence depth range of the cyclic blasting excavation on the surrounding rock damage is 3.4 to 3.6 meters; as the test depth increases, the rock wave velocity curve shows an "S" shape distribution, while the cumulative damage curve of the surrounding rock shows an "inverted S" shape distribution; considering the blasting cumulative damage of the tunnel surrounding rock, the rock state in different depth ranges of the test holes varies, that is, the 0.0 to 2.0 meter depth is the loosening zone, the 2.0 to 3.4 meter depth is the moderately damaged zone, and the 3.4 to 4.8 meter depth is the mild damage zone. The numerical simulation results show that compared with the condition without considering the surrounding rock damage, the distribution area of the plastic zone of the surrounding rock under consi-deration of damage is significantly larger; considering the surrounding rock damage, the maximum arch top settlement after tunnel excavation is 24.01 mm (the average value measured on site is 25.8 mm), and the maximum horizontal convergence is 14.39 mm (the average value measured on site is 15.19 mm), while without considering the damage, the maximum arch top settlement is 20.43 mm and the maximum horizontal convergence is 13.85 mm. This indicates that the simulation results considering the surrounding rock damage have a higher degree of consistency with the actual monitoring data.