Date of Graduation

1990

Document Type

Thesis

Abstract

In this study, a new resistivity method has been developed and tested in three phases; simulated model, similitude model, and field survey. This new resistivity method is a combination of the Bristow arrangement and line electrode method. Three line electrodes are chosen so that the sinkhole electrode is emplaced at far distance from the other two electrodes. Any of the two electrodes and the sinkhole electrode is activated and several resistivity profiles perpendicular to the line electrode are prepared for different electrodes activation. Subsurface cavities cause resistivity anomaly. These anomalies are interpreted and are used to estimate the depths and the dimension of the cavities. Physical simulation of the model was conducted by using a brine tank model in a laboratory. Experimental results appeared to be consistent with the theoretical model. The similitude model study was followed to verify the effectiveness of this method in cavity detection in actual subsurface materials. A similitude model was constructed consisting of five different materials with different thickness and resistivity values to simulate the actual field conditions. A cavity was created in the model and the instrumentation was set up to perform the resistivity survey over the cavity. The resistivity profiles were obtained and interpreted for the different location and size of the cavity. The results of the experiments indicated that the location of the cavity and its dimension can be estimated successfully by this technique. A field resistivity survey was made to confirm the result of the laboratory experiment. A coal mine site employing room and pillar mining system was selected to conduct the resistivity survey. Three line electrodes, each 300 ft. long were buried at 2 ft. depth at distance of 535 and 1039 feet apart. The resistivity survey was performed using 2,4, and 8 feet point potential electrodes spacing. The results of the interpretation indicate that the entry with dimension of 4.5 feet high and 18 feet wide at depth of 85 feet can be detected by this method. The resolution of the detectability of this method shows a great success as compared to other resistivity techniques.

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