Doctoral Degrees (Institute for Groundwater Studies (IGS))

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Browsing Doctoral Degrees (Institute for Groundwater Studies (IGS)) by Author "Du Preez, Michael"

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    Experimental determination of rock hydrological properties using elastic parameters
    (University of the Free State, 2007-11) Du Preez, Michael; Van Tonder, G. J.
    English: As groundwater becomes increasingly vital as a viable source of fresh water in arid or remote areas, where surface water supplies are insufficient to sustain life, agriculture and industry, it has become important to accurately estimate, manage and monitor this valuable resource. Much has been done to improve the management of this precious resource by the development of numerical models that give a realistic estimate on how groundwater reserves will react to changing circumstances in groundwater conditions. The accuracy of these predictions is however limited to the effective accuracy of the predictive model, which in turn relies on accurate data for all the variables which will affect the flow of groundwater. This thesis presents a method to determine hydrological parameters of a rock sample by measuring its elastic parameters, 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 the compressive and shear wave velocities of the rock, by inducing an ultrasonic pulse into one side of the sample and measuring the time it takes the pulse to travel through the sample. The travel times are then converted into compressive and shear wave velocities, which in turn are used to determine the bulk modulus and shear modulus of the sample. • The second method is to use resonant ultrasound spectrography, which measures the natural resonance frequencies of a rock sample induced by an ultrasonic frequency sweep. These resonance frequencies are then analytically verified against the bulk modulus and shear modulus of the rock sample determined by the time of flight method. Both of these methods use apparatus which clamp a cylindrical rock core sample between two sets of ultrasonic transducers. One set of transducers produce compressive ultrasonic waves and the other produce shear ultrasonic waves. An analogue to digital converter is used to read the changing voltage levels in the transducers, induced by the ultrasonic pulse travelling through the sample or the resonant vibrations induced by the ultrasonic frequency sweep in the sample. Once the rock samples elastic parameters are known they are applied to equations which related hydrological parameters to the samples elastic parameters. The resultant hydrological parameter values can then be determined.