United States Department of Transportation
i
Inclinometer - Time Domain Reflectometry Comparative Study
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2004-12-01
[PDF-4.64 MB]
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Edition:Final technical report.
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Abstract:Four pairs of inclinometers and time domain reflectometry (TDR) cables were set up to make a side-by-side
comparison of the performance of these systems in detecting slippage of soils in the shoulders of State Route 124
and State Route 338 in Meigs County, Ohio, within 50 feet (15 m) of the Ohio River. The soil consisted of sandy
silt, silt, and clay on top of sedimentary rock. Borings were located 3-6 ft (1-2 m) from the edge of the pavement on
the 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 at
shear locations on two TDR cables, preventing further monitoring below that depth on each; one inclinometer was
also 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, a
reduction of 34.71%. The data acquisition and analysis equipment costs are $11,245 and $5,110 respectively, for a
reduction of 54.56%. The total savings for a TDR system is 53.74%. For an additional $3105, remote monitoring of
TDR installations can be added, eliminating the need for site visits until the cable becomes damaged; the TDR
system savings even with the remote monitoring are still 27.27% over the inclinometer. Labor time costs for initial
installation are comparable at 8-12 hours, while the reading time is reduced from 10-30 minutes for an inclinometer
to 1 minute for a TDR system. TDR cables also have the advantage that they can be extended to a safer or more
accessible point for reading.
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