Vibration monitoring
Case study: Vibration monitoring of drilling and blasting inside a dam

Within the scope of a refurbishment of an about 100 years old dam a control tunnel should be dug in the longitudinal axis of the wall. Thus the tender for the construction required a drilling and blasting method. The vibrations have to be monitored in the immediate vicinity of the excavation face as well as at the nearby constructions.

For the vibration monitoring in the near-field of the blasting two monitoring stations were installed in drilling holes within the tunnel wall in a distance of 1m and 2m from the excavation face. Further stations were installed on the wall crest near to the tapping point tunnel and in the vicinity (waterworks, restaurant). The monitoring instruments have to be constructed to record vibration velocities up to 400 mm/s and frequencies up to 1000 Hz.

During the monitoring the given limits of 200 mm/s at a distance of 1 m from the excavation face and 100 mm/s at a distance of 2 m from the excavation face were partly exceeded especially within the first two months of the work. After adjustment of the blasting parameters the vibrations generated by blasting remain within their limits. Due to the high resolution in time some problems of the ignition process could be carried out (e.g. differences of the ignition timings). The influence of the blasting on the buildings in the vicinity of the dam was very small (<1mm/s).

Fig. 1: View on the dam

Fig. 2: Vibration velocities of a single component for the single ignition stages