Cross-hole acoustic measurements in basalt
A series of cross-hole acoustic measurements have been performed in a columnar-jointed basaltic rock mass around an underground opening mined by the drill-and-blast method. The purposes of the test program were: to evaluate the rock mass characteristics around the opening; to determine the zone of blast damage; and to evaluate seismic methods for anomaly detection ahead of mining in this type of rock. The cross-hole measurements were made between four 76-mm diameter horizontal boreholes diamond-drilled 12 m into a wall of the underground opening. Repetitive pulses of compressional (P) and shear (S) waves of frequencies in the range 1 kHz to 100 kHz were propagated from a transmitter sonde through the rock mass to a receiver sonde, both of which were clamped hydraulically to the borehole wall. After amplification the received P- and S-wave signals were digitized at the surface by a digital oscilloscope and stored on floppy discs. The results indicate considerable reductions in P- and S-wave velocities at distances less than 2 m from the face. Beyond 2 m, the velocities in a vertical direction indicate almost constant values. The velocities in the horizontal direction beyond 2 m appeared erratic, but showed a general tendency to increase as a function of distance from the face. 19 references, 10 figures.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6846484
- Report Number(s):
- LBL-17521; CONF-840633-12; ON: DE84010781
- Country of Publication:
- United States
- Language:
- English
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