HR: 0830h
AN: S51D-0081    [PDF]
TI: Vibration Response as an Indicator of Ground Fall Hazards in Mining: An Investigation Using Laser Doppler Vibrometry
AU: * Swanson, P L
EM: pswanson@cdc.gov
AF: National Institute for Occupational Safety and Health, Spokane Research Laboratory, 315 E. Montgomery Ave., Spokane, WA 99207 United States
AU: Rettkowski, J D
EM: jrettkowski@cdc.gov
AF: National Institute for Occupational Safety and Health, Spokane Research Laboratory, 315 E. Montgomery Ave., Spokane, WA 99207 United States
AU: Caley, A B
EM: acaley@cdc.gov
AF: National Institute for Occupational Safety and Health, Spokane Research Laboratory, 315 E. Montgomery Ave., Spokane, WA 99207 United States
AB: Unexpected falls of ground are one of the leading sources of injuries and fatalities in U. S. underground mines. A primary means of assessing mine-roof integrity is the age-old method of roof sounding where a miner taps on the roof and listens to the resulting seismically coupled acoustic response. Impacts to loose, hazardous blocks of rock generally produce a hollow drummy sound that is anomalously low in frequency and long in duration compared to sounds from competent rock. In this study, a noncontact laser Doppler vibrometry (LDV) method is used to record vibrations on rock surfaces to (i) evaluate the feasibility of remotely detecting hazardous ground from safe positions and (ii) delineate the fundamental, and little-studied, mechanical processes attending such gravity-driven failures. During the technique development stage, measurements were obtained on various rock outcrops and other structures with known defects; these included single-point and two-dimensional array recordings. Excitation sources included local and remote impacts, and ambient and forced vibrations. Consistent with predictions from simple models of elastic blocks coupled to solid ground through low-stiffness interfaces, loose rocks were effectively delineated with simple broadband RMS measures of elevated particle velocity. Other narrow-band spectral measures were also investigated and observed to be sensitive to block geometry, interface boundary conditions, and excitation source characteristics. In most of the experiments, loose blocks could be identified, in a comparative sense, even without compensating for the attendant vibration of the LDV. To deliver useful vibration response information to miners and others exposed to these hazards, two options are being explored: (i) development of 2-D maps of vibration response superimposed on target images and (ii) conversion of single-point LDV output into audible signals for use in a qualitative comparative mode.
DE: 0994 Instruments and techniques
DE: 5104 Fracture and flow
DE: 5144 Wave attenuation
DE: 7294 Instruments and techniques
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting