Discussion

MR. D. C. MANN, JMP Consultants Ltd, Glasgow Ideally trial blasting should be carried out using full scale charges, but as the Authors of Paper 34 point out this is seldom possible. Therefore, it is necessary to use small scale charges and, as a result, geophones must be placed quite close to the explosive source. What advice would the Authors give regarding the number and size of the small scale charges for trial blasting, and at what distances should the geophones be placed (an important consideration according to Fig. 5 of Paper 34)? As much larger charges are used during construction and the locations for monitoring vibrations are normally at greater distances than those used in the trials, how reliable are the regression lines produced by the trial blasting? The Paper suggests that the trial blasting provides an upper bound regression line. Is this likely to be true in all cases?