DEVELOPMENT OF CONTROLLED IMPULSE TECHNIQUE FOR IN SITU TESTING OF ROCK
Technical rept., Jun 1964-Jul 1965
BUREAU OF MINES DENVER CO
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Object of the work is development of equipment and techniques for transmission of nondestructive, repetitive, stable, closely controlled-shape sonic pulses through various types of rock in place. Rock masses tested were granitic gneiss schist, potash rich salt beds, and porphyry-copper ore. The tests measure some physical properties of a rock mass over various periods of time. Sonic pulses are produced by electronically excited, piezoelectric-ceramic transducers housed in transmitter and receiver units. Electronic pulses for transducer excitation are generated by transistorized battery-powered pulse generators. Output from receiver units or geophones, amplified by transistorized preamplifiers, is led into a portable transistorized oscilloscope triggered by the electronic pulse generator to display the signal. Various models of transmitter and receiver units differing in size, weight and manner of insertion into boreholes in rock are described. Two models of electronic pulse generators and a receiving unit preamplifier are described. Transmission distances attained varied from 55 feet in strongly hydrothermally altered porphyry copper ore to 1,373 feet in sylvitehalite. Data obtained could be used to compute dynamic moduli of rigidity and elasticity. Under proper conditions, data were obtained that revealed development or presence of permanent rock- structure damage.
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