By A. Roberts
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BUTKOVICH, T. , Calculation of the shock wave from an underground nuclear explosion in granite, in Peaceful Applications of Nuclear Explosives, Plowshare, 1965. 44. COOK, Μ. , The Science of High Explosives, Reinhold, New York, 1958. 45. DUVALL, W. I. , Spherical Propagation of Explosion-generated Strain Pulses in Rock, U S Bur. , Rep. Invest. N o . 5483, 1959. 46. RINEHART, J. , The role of stress waves in the comminution of brittle, rock-like, materials, Int. Symp. on Stress Wave Propagation in Materials, Penn.
Auberger and Rinehart, measuring attenuation in rocks over the 100 kHz to 2 M H z range, found that attenuation peaks occurred at harmonic frequencies which could be related to the predominant grain size in the rocks. It appears that when the length of the energy pulse approaches the grain size of the rock the constituent crystals are set into resonance, which causes local increase in the attenuation/frequency relation. Krishnamurthy and Balakrishna [ 4 7 ] have also determined attenuation characteristics for several rocks.
40 60 Frequency (kHz ) FIG. 16. Frequency response of calcareous sandstone (Attewell and Brentnall ). 27 Applied Geotechnology Limestone Sandstone 1 2 3 4 5 25 —j (-76-^6~4-»76»j~76H*76*f»76*f»76^ mm 0 20 40 60 80 100 1 2 3 4 5 6 | * 7 6 - ^ Ι - ^ Ι · ^ Ι ^ ΐ · + « ΐ · + · - 7 6 -^»76 *j mm 0 20 Time, t (/is) (a) FIG. 17. Superposed pulses, with a common time origin, for limestone and sandstone ( Ricketts and Goldsmith ). Such a condition is intended to produce best possible coupling. Subsequent experiments by Personn et ai , exploring the effects of the larger diameter drill-holes that are now feasible using contemporary drilling techniques, quote the results shown in Fig.