Wambo Coal AEMR 2011-2012 - Peabody Energy

• individual wall panels — 20 Hz to 40 Hz;
• ceilings — 15 Hz to 30 Hz (the form of the roof structure in the Wambo house is not known,
and possible shorter framing member spans result in higher frequencies).
These frequencies are relevant for blast design in that, if a ground vibration is similar to a characteristic building
frequency, the action can be greatly magnified. Theoretically, a maximum amplification of 50× is possible at resonance
for a single-degree-of-freedom structure and structure amplifications of more than 20× have been measured during
blasting events in or near Hunter Valley mines.
3
2 THE ASSESSMENT
2.1 Monitoring
Recording instrumentation was set up on two occasions when blasting was being carried out in the Homestead Pit,
on 16 December 2011 and 17 February 2012, with ground vibration PPV levels recorded at the Homestead monitor
of 4.07 mm/s and 1.68 mm/s respectively. Instrumentation was set up in the house on the first occasion and the first
floor of the kitchen wing on the second. Figure 1 shows the sensor locations for the two events.
Figure 1: Positions of accelerometers
for the two monitored events. The
New House was monitored on 16
December 2011 and the Kitchen Wing,
first floor, on 17 February 2012.
The wall mounted accelerometers were,
in each case, mounted at the tops of
the walls. The numbers relate to the
vibration recording data and are the
channel numbers used on the recorder.
( Base drawing from EJE Architecture)
2.1.1 THE NEW HOUSE (16/2/2011)
Three accelerometers were set up in a front room of the new house where the wall and ceiling dimensions were
judged to be of a size which might make them vulnerable to out-of-plane resonant vibration at the expected blast wave
frequencies: one sensor was fixed near the middle of the ceiling, one just below the ceiling on the front wall and one
just below the ceiling near the middle of the wall adjoining the front hallway.
Photographs of the installation are shown in Figures 2 to 5.
The seismic recorder is fitted with a GPS receiver which gives time accuracy to better than one millisecond. The
current ground monitor is not accurately timed and is understood to have an internal clock which is reset periodically.
If times of similar accuracy could be obtained from both recorders, then observation of arrival times in the building
could be correlated with different stages of the blast wave, allowing better indication of the activating vibration.
April 2012
Wambo Homestead
Vibration vulnerability