engleski

The role of position on initiation and stemming of breakage

The course of motorway tunnel under construction was set only 2 m away from the main motorway. Tickness of the tunnel overburden rock was 9 m. During the tunnel construction the traffic on the motorway was not supposed to be interruped. The tunnelling was carried out by NATM and classical drilling of blastholes and by blasting. For the purpose of evalution of possible damage of the rock burden above the tunnel, meaning also a possibility of motorway damage and possible interruption of traffic, measuring of seismic effects of blasting on the surface was carried out with intention to define the safe mode of blasting. Because of the thin overlayer it was possible to place the instrument 10 m away from the place of blasting. Along with the measuring of influence of a dynamic component of blasting on the surrounding rock mass, it was also measured the influence of position of initiation and stemming of blastholes on the rate of breakage. Several pairs of blastholes were drilled, changing the position of initiation of blasting charge, and the mode of stemming, but with exactly the same amount of explosive charge. After blasting the lenght and volume of the breakage was measured for the each blasthole. The results of measuring showed that the greatest breakage was achieved by initiation from the top of blasthole at almost equal dynamic effest of blasting.

blasting; position of initiation; stemming

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