Environmental Engineering Reference
In-Depth Information
2.0
2.0
1.0
1.0
0.1
0.1
Sands
0.01
0.01
Clay
0.001
0.001
0
20
40
60
80
100
Percent failure stress
FIGURE 4.22
Average acoustical emissions amplitude (peak signal voltage output) vs. percentage of failure stress in triaxial
creep (5-psi confining pressure).
Note
: ( ) concrete sand (soil 3); ( ) Ottawa sand (soil 2); ( ) Kaolinite clay
(soil 6). (From Koerner, R. M. et al.,
Proc. ASCE, J. Geotech. Eng. Div
. 103, 837-850, 1977. With permission.)
Tape
recorder
Amplifier
Filter
Transducer
Preamplifier
Field cable
Oscilloscope
FIGURE 4.23
Simplified diagram of typical microseismic field-monitoring system. (From Hardy, H. R., Jr. and Mowrey, G. L.,
Proceedings of the 4th International Conference
, Zurich, April, A. A. Balkema, Rotterdam, pp. 75-72. With
permission.)
Sensors
Geophones can detect signals in the frequency range of 2 to 1000 Hz, the normal seismic
energy range for large geologic structures. They are generally used as sensors to monitor
mines and tunnels because of their greater sensitivity in the lower frequency ranges
(Hardy and Mowrey, 1977). Accelerometers are employed for high-frequency components
(
f
1000 Hz), and displacement gages are employed for very low-frequency ranges
(
f
1 Hz).
