Collaborative Research: Evaluation of 2D vs. 3D Multielectrode Resistivity for the Characterization of Shallow Karst

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CMS-0201020PI: Jonathan NyquistInstitution: Temple UniversityTitle: "Collaborative Research: Evaluation of 2D vs 3D Multielectrode Resistivity for the Characterization of Shallow Karst"Sinkholes in areas with soluble bedrock (e.g., limestone and dolomite) are a cause of cost overruns during construction and of structural failures. These areas can be found in 15% of the United States and estimated costs of failures caused by sinkholes in eastern central Pennsylvania since 1975 exceed 30 million dollars. The frequency of these problems can be reduced by improving methods for locating subsurface voids that cause sinkholes. Two-dimensional earth-resistivity testing has been demonstrated to be useful, but because 2D geometry is assumed, this method has limited ability to determine void size and orientation. Features adjacent to the 2D resistivity line and directly below the line affect the results. Three-dimensional resistivity tests are time-consuming and do not provide sufficient detail for geotechnical investigations unless thousands of electrodes are used.In this project, interpretation of resistivity data is being improved by comparing two field methods. The first method incorporates multiple 2D resistivity lines into three-dimensional models. The second method develops large 3D data sets from multiple smaller, overlapping 3D surveys. Both approaches should be able to determine void geometry by developing a 3D resistivity model from data collected with a practical number of electrodes. To test the methods, the geometry of a natural subsurface cave is being mapped and resistivity results over the cave are compared to actual cave geometry. The project will result in an improved investigation strategy for sites located in sinkhole areas. Two additional features of this project should be noted. First, the project is being conducted at a site that has been used by other researchers. Further characterization of the conditions at the site will encourage additional collaboration to test new investigation methods. Second, the project involves collaboration of an undergraduate institution with a graduate institution. Such collaboration will encourage students to obtain post-graduate education.