Potential of Airblast Overpressure and Ground Vibration from Quarry Blasting to Increase the Frequency of Rockfalls on Mt. Coonowrin

Mount Coonowrin located in the Sunshine Coast hinterland north of Brisbane, is one of a scattered group of peaks and hills that constitute the Glasshouse Mountains and which is protected within the Glasshouse Mountains National Park. Concern about visitor safety in relation to rockfalls on the mountain were supported by the results of two geotechnical studies and led to the closure of this section of the National Park. The rockfall problem has become the focus of renewed community concern since 1998, and some sections of the local community believe that blasting from a nearby quarry is causing an increase in the incidence of rockfalls. A.joint study was carried out by the Environmental Protection Agency and the Department of Natural Resources, Mines and Energy to investigate whether the quarrying activities were having an impact on the stability of the mountain. The report [1] describes the primary investigation which included the monitoring of a series of blasts at four locations on three days and modelling of the results to quantify the ground vibration and airblast overpressure currently occurring at the base of the mountain and at more remote locations. This paper describes the model (in terms of site laws) subsequently used to predict future ground vibration and airblast levels at the mountain as quarrying progressively approaches the National Park. The site laws will be used to optimise blast design, maximising blast efficiency while ensuring that vibration and airblast limits are not exceeded. An extensive literature search of Australian and overseas standards and guidelines has shed no light on ‘acceptable’ ground vibration and airblast overpressure criteria to avoid triggering rockfalls from potentially unstable natural rock faces.