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The data was interpolated between the survey lines using ArcScene to create a pseudo 3-dimensional model to identify key components of the slope creep. Topographic corrections were made using GPS and elevation data collected the same day as the ERT survey. These 10 profiles were processed using Geotomo's Res2DInv software. We used an inline dipole-dipole array with electrodes spaced 2 meters apart (with a minimum 'a' spacing of 2 meters and a maximum was 4 meters the minimum 'n' value was 1 and the maximum was 8). Nine profiles were 80 meters long and one was 40 meters long, with 10 meter spacing between each profile. We surveyed 10 parallel ERT profiles using an ABEM Terrameter SAS 4000. The purpose of this study was to image the failure associated with the subsurface creep in the fill and to identify the subsurface engineering works that may be interacting or moving with the creep. The fill has been steadily creeping since initial construction and has caused severe damage to the highway above on several occasions. Water is currently conveyed through the channel in a box culvert underneath the embankment. The fill is over 15 meters (~50 feet) at its deepest point and sits partially in an old stream bed. The failure surface associated with the creep was also identified, and mapped in three dimensions.Ībstract = "In May 2017, we carried out an electrical resistivity tomography (ERT) survey of the downslope embankment of a state highway in central Illinois where creep failure has been observed for over 50 years.
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Several underground objects were identified, including metal and plastic drainage pipes, a chimney drain, the box culvert, and possible groundwater plumes from recent rainfall events. In May 2017, we carried out an electrical resistivity tomography (ERT) survey of the downslope embankment of a state highway in central Illinois where creep failure has been observed for over 50 years.