INVESTIGATION OF LONGITUDINAL CRACKS ALONG KICKAPOO DAM, BRONTE, TX USING RESISTIVITY SURVEYS

In March and May of 2017 students and faculty from Angelo State University assisted government personnel who had been contracted to determine the cause of the longitudinal cracking along the top surface of Kickapoo dam Site 4 in Bronte, TX by running resistivity surveys at the site. Cracks in the top surface of the dam run the length of the dam with some reaching depths of 7 feet or more. Resistivity profiles were run using a Super Sting resistivity system with 112 electrodes and run-alongs were utilized in order to image all the way to the bottom of the dam at ~50 feet. The 5 longest lines located at the top of the dam were 750 feet long and reached a depth of 64 feet. Two additional lines were run across the profile of the dam which provided cross sectional views of the 5 previously stated lines. Preliminary modeling of the resistivity lines show areas of high resistivity, some in the shape of channels, believed to coincide with the local bedrock (San Angelo sandstone). A large area of low resistivity stretches across the profiles at the top of the dam that varies in thickness from ~8 feet to ~24 feet. Thin (~10 feet wide) areas of low resistivity stretch vertically from the surface into the dam, reaching depths of 32 feet to 64+ feet below the surface of the dam. Two of the localized, low resistivity areas coincide with the location of the old channel and the outflow pipe; however, the rest appear to coincide with areas of cracking at the top of the dam. One thing to note is that the low resistivity areas do not coincide with every area of cracking found at the surface of the dam. In addition to the resistivity survey, test pits were dug in the back side of the dam and samples of the various soil levels were collected for analysis.