Vibration measurements in the damage zone in tunnel blasting
Ingvar Bogdanoff
Abstract
During blasting of an access tunnel in a rock cavern in Stockholm city, vibration measurements were done at distances between 0,25 and 1m outside the tunnel perimeter holes. The perimeter and the perimeter helpers were charged with conventional smooth -blasting explosives. Electronic detonators were used with 1 ms delay time between the perimeter holes. This initiation technique is known, as “shear blasting”. The measurements gave the duration -times for the high level vibrations in the damage zone. The duration - time is closely related to the principal frequencies and must be evaluated when very short delay times are used. The peak particle vibration levels (PPV) were 2 - 2,5 times higher than the normally expected value, at the distances for normally expected rock damages. The problems of resonance between the accelerometer probe and the resonance in the rock were solved by small accelerometer probes and digital filtering technique.