Ground Vibrations Generated by Blasting

Abstract

In tunnel driving through hard or soft rocks, the use of blasting has been a conventional and typical excavation method, as well as more efficient and economical. With the demands of tunnels and the development of rock blasting technique, the question of ground vibrations has become increasingly important, and it has become more or less routine to excavate rocks close to or below houses and buildings. Blasting is carried out for the purpose of fragmenting and demolishing rocks for removal by utilizing the vast energy which the explosion of explosives generates. Near the explosive charge, the high amplitude stress wave and borehole gases produced by the detonation process crate crushed and fractured zones. Beyond these zones, where the amplitude of the stress wave does not exceed the strength of rock, the wave is propagated elastically. The elastic stress waves spread out in all directions and cause the surface of the underground opening to oscillate as a free surface. If the amplitudes of the wall vibrations, and particularly of the roof vibrations, are sufficiently high, loose blocks of rock may be dislodged or fractures in rock may be extended, further weakening the tunnel. The empirical propagation equation is discussed with the consideration of following : a) particle velocity, b) distance from blasting point, c) types of explosive, d) quantity of charge, e) method of initiation, f) drilling pattern, g) path of propagation, h) tamping condition, i) characteristics of ground and j ) state of ground formation.