Slope Stability Monitoring Using Remote Sensing Techniques

During the past six years the Arkansas State Highway and Transportation Department (AHTD) has spent over nine million dollars repairing slope failures that have occurred in the state of Arkansas. Specifically, higher than average precipitation in 2004 and 2008 led to large quantities of slides, all of which were repaired. Two highways, within the state of Arkansas, with known historical movements along or across the highways are being monitored using traditional surveying techniques and advanced remote sensing techniques. These slides, both of which are located in fill slopes. One a 500-foot long slide located north of Chester, Arkansas, within the median of Interstate I-540. The other site is a 1200-foot long slide located east of Malvern, Arkansas, cutting across all four-lanes of Interstate I-30, have visible evidence of movement (tension cracks, traverse cracks, head scarps, flank displacement, etc.) A ground portable RADAR interferometer (GPRI-II) constructed by Gamma Remote Sensing is the first device in the United States being used to remotely monitor slopes. Surveying monuments (2.5-inch diameter aluminum monuments placed on 24-inch long, ½-inch diameter rebar encased in 6-inches of concrete) were installed inside and outside of the sliding mass at each site (29 monuments at the calibration site in Chester, Arkansas site and 54 monuments at the validation site in Malvern, Arkansas), and are being monitored using traditional surveying techniques (using a Nikon DTM-520 total station) to identify the movement of each monument as detected from two observation points. The GPRI-II and a Leica C-10 LIDAR are also being used to identify the movement of the slopes. Inclinometers have been also installed at the validation site near Malvern, Arkansas to compare the displacements obtained by remote sensing techniques with standard borehole slope monitoring methods. The results of the movements observed using in-situ instrumentation, total station, RADAR, and LIDAR are discussed. A full geotechnical subsurface investigation was perform at the validation site in Malvern, Arkansas during the summer of 2011. The drilling and sampling investigation provided the necessary soil and rock samples for laboratory testing. The results from the laboratory tests permitted the displacement rates to be inspected in the light of the shear strength of the soil strata and the depth to the shear failure plane. Since December 2010, site visits have been conducted every two weeks for the Chester site and every month for the Malvern site. During each visit total station, RADAR, and LIDAR observations were conducted