Inclinometer - Time Domain Reflectometry Comparative Study

2004PDFTech ReportSargand, Shad M.Sargent, LisaFarrington, Stephen P.Ohio Research Institute for Transportation and the EnvironmentOhio. Dept. of Transportation. Office of Research and DevelopmentUnited States. Federal Highway AdministrationOhio Research Institute for Transportation and the EnvironmentOhioShear strengthSoils by strengthTime domain reflectometersTestingShear strength of soils--TestingInclinometer--TestingTime-domain reflectometry--TestingFHWA/OH-2004/01014798(0)Final technical report.Four pairs of inclinometers and time domain reflectometry (TDR) cables were set up to make a side-by-sidecomparison of the performance of these systems in detecting slippage of soils in the shoulders of State Route 124and State Route 338 in Meigs County, Ohio, within 50 feet (15 m) of the Ohio River. The soil consisted of sandysilt, silt, and clay on top of sedimentary rock. Borings were located 3-6 ft (1-2 m) from the edge of the pavement onthe shoulder of the road at two locations on each road, with a TDR and an inclinometer located 3-5 ft (1-1.7 m)apart. Borings extended 10 ft (3.3 m) into the bedrock. Sixteen monthly readings were taken.At all four locations, the inclinometers detected shearing at depths ranging from 16 ft (4.9 m) to 40 ft (12.2 m).All of the detected shears were also identified by the TDR cables to within 1 ft (0.3 m). Water leakage occurred atshear locations on two TDR cables, preventing further monitoring below that depth on each; one inclinometer wasalso deformed beyond use at the same depth as the corresponding TDR cable water leakage.The cost for materials and casing for a single inclinometer installation is $484, versus $316 for a TDR, areduction of 34.71%. The data acquisition and analysis equipment costs are $11,245 and $5,110 respectively, for areduction of 54.56%. The total savings for a TDR system is 53.74%. For an additional $3105, remote monitoring ofTDR installations can be added, eliminating the need for site visits until the cable becomes damaged; the TDRsystem savings even with the remote monitoring are still 27.27% over the inclinometer. Labor time costs for initialinstallation are comparable at 8-12 hours, while the reading time is reduced from 10-30 minutes for an inclinometerto 1 minute for a TDR system. TDR cables also have the advantage that they can be extended to a safer or moreaccessible point for reading.95