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Blasting operations conducted at surface mining operations often consist of one million pounds of explosives or more being detonated within a few seconds. These large detonations may produce ground vibrations that travel off the mine property affecting natural and man-made structures near the mine. The amplitude and frequency content of these ground vibrations may cause cracking in natural rock structures or actual spalling of rock from sensitive areas. Natural structures such as pictographs (symbols and pictures carved into rock by ancient cultures) often tell a story from the past and are recognized and protected for their archaeological significance.
Matheson Mining Consultants, Inc. were hired to monitor and analyze vibration data obtained from digital seismograph recordings at a pictograph panel. The maximum ground vibrations recorded at the pictograph panel (pictured below) were 0.215 ips and the maximum air overpressure recorded at the panel was 124 dBL. These numbers are well below the levels (25 ips) that would typically be required to cause damage to a rock mass (Oriad, Dynamic Effect on Rock Masses from Blasting Operations, 1970). The mine’s permit states that vibration and overpressure levels shall not exceed 1.0 ips and 133 dBL respectively. |
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Permanent monitoring stations are used to monitor blasting activities in areas that are difficult to access or that require constant monitoring. |
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Protecting Pictographs in in Big Horn County, Montana |
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Seismograph Rental & Sales |
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Matheson Mining Consultants, Inc. |
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Colin Matheson operating a Blastmate III vibration monitor. |
