Experimental determination of rock hydrological properties using elastic parameters

[摘要] English: As groundwater becomes increasingly vital as a viable source of fresh water in aridor remote areas, where surface water supplies are insufficient to sustain life,agriculture and industry, it has become important to accurately estimate, manage andmonitor this valuable resource. Much has been done to improve the management ofthis precious resource by the development of numerical models that give a realisticestimate on how groundwater reserves will react to changing circumstances ingroundwater conditions. The accuracy of these predictions is however limited to theeffective accuracy of the predictive model, which in turn relies on accurate data for allthe variables which will affect the flow of groundwater. This thesis presents a methodto determine hydrological parameters of a rock sample by measuring its elasticparameters, using non-destructive ultrasound methods.This is done in two ways;�?The first of these is call the time of flight method. This method measures thecompressive and shear wave velocities of the rock, by inducing an ultrasonicpulse into one side of the sample and measuring the time it takes the pulse totravel through the sample. The travel times are then converted into compressiveand shear wave velocities, which in turn are used to determine the bulk modulusand shear modulus of the sample.�?The second method is to use resonant ultrasound spectrography, whichmeasures the natural resonance frequencies of a rock sample induced by anultrasonic frequency sweep. These resonance frequencies are then analyticallyverified against the bulk modulus and shear modulus of the rock sampledetermined by the time of flight method.Both of these methods use apparatus which clamp a cylindrical rock core samplebetween two sets of ultrasonic transducers. One set of transducers producecompressive ultrasonic waves and the other produce shear ultrasonic waves. Ananalogue to digital converter is used to read the changing voltage levels in thetransducers, induced by the ultrasonic pulse travelling through the sample or theresonant vibrations induced by the ultrasonic frequency sweep in the sample. Oncethe rock samples elastic parameters are known they are applied to equations which related hydrological parameters to the samples elastic parameters. The resultanthydrological parameter values can then be determined.

[发布机构] University of the Free State