Abstract
Aiming at surrounding rock damage induced by dynamic disturbance from blasting excavation of rock-anchored beam in rock mass at moderate or far distance in underground cavern, numerical model of different linear charging density and crustal stress in underground cavern is established by adopting dynamic finite element software based on borehole layout, charging, and rock parameter of the actual situation of a certain hydropower station. Through comparison in vibration velocity, contour surface of rock mass excavation, and the crushing extent of excavated rock mass between calculation result and field monitoring, optimum linear charging density of blast hole is determined. Studies are also conducted on rock mass vibration in moderate or far distance to blasting source, the damage of surrounding rock in near-field to blasting source, and crushing degree of excavated rock mass under various in situ stress conditions. Results indicate that, within certain range of in situ stress, the blasting vibration is independent of in situ stress, while when in situ stress is increasing above certain value, the blasting vibration velocity will be increasing and the damage of surrounding rock and the crushing degree of excavated rock mass will be decreasing.
Highlights
Jinsha River Basin, which lies on the upstream of Yangtze River in China, has witnessed the development and construction of large numbers of water conservancy and hydropower projects
The rock-anchored beam is widely used in hydropower projects as the essential construction in underground caverns which makes the first success in Norway [1, 2]
The following conclusions could be drawn according to the analytical comparison of dynamic finite element calculation and on-site test: (1) The vibration velocity test of three directions of surrounding rocks in moderate and far area blasting excavation of rock-anchored beams found out that the vibration velocity of rock mass perpendicular to the blasting excavation surface is the largest which should be used as the reference of vibration velocity control in rock mass excavation
Summary
Jinsha River Basin, which lies on the upstream of Yangtze River in China, has witnessed the development and construction of large numbers of water conservancy and hydropower projects. The rock-anchored beam is frequently used as the load bearing of crane in caverns in order to reduce the span of underground powerhouses and accelerate the progress of construction. The application of rock-anchored beam has several advantages It can reduce the excavation span of underground caverns which benefits the surrounding rock stability and the amount of excavation of tunnels and make it possible to install the crane in advance and brings convenience for concrete placements of caverns and unit installation. The research adopts threedimensional models in the calculation of vibration speed of the blasting of rock mass in the moderate and far distance and two-dimensional models in the simulation of crushing conditions of rock mass in near-field of blasting sources and explosion. The paper does the study of rock mass vibration in the moderate or far distance of blasting, the damage of surrounding rock in near-field of blasting source, and crushing degree of excavated rock mass under different crustal stress
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