Combined blast and vibratory machines effect on in-service structures

Abstract

Large cement storage towers are commonly exposed to both quarry production blasting and the excitations from vibratory plant. Several seismographs were placed in the quarry to monitor blast-induced vibrations in the vicinity of the cement plant. Moreover, two ultra-sensitive vibration acquisition stations were installed respectively, at the bottom and at the top of the cement storage tower. Both stations were synchronized allowing them to be set on the same time scale. An advanced processing procedure was adopted in order to separate the effect of each excitation (i.e. blasting and vibratory machines). The wall displacements/strains were then estimated at both ends of the tower. The frequencies associated with the vibratory machines showed a noticeable dominance comparing to the waves linked to the blasting activities and eventually higher than the natural frequency of the structure. Ultra-high excitation frequencies led to the amplification of the vibrations induced from the vibratory machine for both events. Vibrations from the production shots as well as those from the vibratory machines has been found to have minor effect on the structural integrity of the tower, with induced strains fall below the critical thresholds that may cause cracking within the tower’s walls.

Keywords

• Large structure
• Vibratory machines
• Blasting
• Strains
• Time frequency analysis
• Vibrations