I write in response to Lucy Philip's Talking Point in your August issue, on problems encountered when vibration limits are set at low levels.
As she points out, there have been few, if any, cases of damage to structures as a result of blast induced vibration from civil engineering projects. The conservative damage criteria levels set by British Standards include the huge amount of field data held by the recently defunct United States Bureau of Mines. These data sets were considered to be the most reliable anywhere and proved to be of enormous value to other countries when drafting their own standards.
At Vibrock we have been closely involved with blast design and monitoring of ground vibration from blasting for the past 25 years. Twenty years ago, it was not so easy to accurately measure ground vibration and thus difficult to quantify levels generated by blasting. Generally the limit of peak particle velocity (PPV) was 50mm/s, equivalent to a foot stamp on a wooden floor measured at a distance of 1m. There was no damage to property from blast induced vibration at this level, but sophisticated monitoring instrumentation began to emerge allowing comparisons to be easily made. Every decade or so these levels have been halved for the reasons given by Lucy Philip and are now so low, in many cases, as to virtually preclude the use of explosives.
Vibrock recently completed a two and a half year study on the environmental effects of blasting, commissioned by the Department of Environment, Transport and the Regions. The resulting publication, which discusses the five potential environmental consequences of blasting (ground vibration, air overpressure, noise, dust and flyrock) is available from the Stationery Office (ISBN 0-11-753412-9).