Evaluation of Ultrasonic Velocity Tests to Characterize Extraterrestrial Rock Masses

This thesis investigates the use of ultrasonic pulse velocity (UPV) tests for extraterrestrial rock characterization by evaluating the effects of physical sample properties on the signal attenuation of ultrasonic waves. An initial review of standard laboratory UPV testing methods and expected space conditions isolated four key disparities between the two testing environments: (1) sample dimensions, (2) regolith cover, (3) sample surface roughness, and (4) utility of a gel couplant. Laboratory tests were then performed to assess the influence of these parameters in simulated space conditions, using concrete beams to simulate large sample sizes, and ground limestone to simulate regolith cover. The ensuing data analysis identified strategies to ensure adequate signal transmission and data interpretation.;Overall, the experimental results show that the signal attenuation curves can be constructed and simple regression curves can provide estimations of the true P-wave velocity even without a gel couplant. For the case of large sample sizes, simple exponential regression of the measured P-wave velocity at various transmission lengths can be extrapolated to zero length to estimate the true value. For the case of regolith cover, the particle top size and particle size distribution affect signal attenuation; however, an exponential fit to measured velocity versus depth data can be used to accurately predict true sample velocity at zero depth. Additionally, testing with rough samples showed that compacted regolith can be used to ensure contact between the sample and the UPV transmitter, and this method produced similar attenuation curves to those determined from smooth samples. Altogether, these data indicate the reliability of UPV to characterize material in-situ; however, without a gel couplant, UPV measurements become increasingly imprecise. (Abstract shortened by ProQuest.)