Open Cut » Environment
Blast overpressure levels experienced from operations on open cut mines depend on many factors including the design of the blast, the distance from the blast to the receiver and the prevailing atmospheric conditions. The way in which temperature and wind vary along the path through which the over pressure wave travels from the source to the receiver is particularly important in determining the overpressure experienced at the receiver.
The purpose of ACARP Project 12036 was to provide mine operators with information on meteorological conditions that will allow the effects of atmospheric conditions to be taken into account before making the decision to blast. The approach taken has been to use the MM5 mesoscale meteorological model with 24-hour hour forecasts from the Bureau of Meteorology supplemented with local observations of wind speed, wind direction and temperature in the lower atmosphere, to predict three-dimensional meteorological fields in the Hunter Valley. MM5 is a meteorological model managed by the National Centre for Atmospheric Research (NCAR) at Boulder, Colorado. The local observations were provided by a SODAR and RASS centrally located in the modelling domain. In addition wind speed and direction data from ground based sensors are also supplied to the MM5 model.
The Bureau of Meteorology data supplied to the model cover the area known as the Sydney Domain, which has Sydney at the approximate centre. The domain extends in a north-south direction from 38 degrees South to 30 degrees South and in an east-west direction from 147 degrees to 156 degree East. These data are provided to the MM5 model at user-determined intervals. MM5 runs over two nested grids. The inner-most grid covers a square area 75 by 75 km with a grid spacing of 3 km by 3 km. The centre of the grid coincides approximately with the centre of open cut mining in the Upper Hunter Valley. The model is run at least once a day and also at user selected intervals. The model output is analysed to provide predicted vertical profiles of wind speed, wind direction and temperature, extending from ground-level up to 1.6 km. Each time the model is rerun it assimilates local meteorological observations provided by the SODAR, RASS and other surface stations. At this stage only one surface station is used. These data are used to nudge the model predictions to the observed values.
The model results are reprocessed to tabular and graphical summaries at selected sites coinciding with mine sites and other sites of interest. Data are uploaded to a public web site. Users can obtain data on wind and temperature profiles for any area of interest on the grid in a format suitable for input to a blast overpressure prediction model provided by Terrock Pty Ltd or for any other use.
The report provides a brief review of how the model predictions are ultimately used to predict the enhancement of blast overpressure levels. This is done using a model provided by Terrock which uses MM5 data to predict (1) the level of enhancement (positive and negative) caused by meteorological conditions and (2) the absolute level of overpressure resulting from a blast. The results are presented as contour plots overlaid on a map of the area surrounding the blast. An example showing blast overpressure enhancement is provide. The results are promising and the system appears to be a useful tool, in its current state of development, to improve the management of impacts from blasting.