Comparison of TDR and Inclinometers for Slope Monitoring

As TDR technology grows in acceptance, its use stimulates further innovative applications and comparison with slope inclinometer measurements. This paper presents cases in which the opportunity arose to compare these two technologies to detect and measure subsurface deformation in slopes. Among the main points addressed are (1) the comparison of TDR reflection magnitude and inclinometer incremental displacement to help quantify deformation with TDR technology, and (2) the comparison of the accuracy of the two technologies in detecting and measuring shear deformation in localized versus general shear. Case histories are presented that involve monitoring movement in soil and rock slopes and embankments as well as retrofitting deformed inclinometer casing with coaxial cables. This paper describes installation details. When monitoring to detect narrow shear zones in soils, it is best to use small ratios of hole-to-cable diameter, and prudent use requires that larger diameter, solid, metallic coaxial cables be installed in separate holes. Grout strength should be (1) low enough to fail before bearing capacity of the surrounding soil is reached, and (2) high enough to deform the cable it encapsulates. It is recommended that other users publish cases in which theses two technologies are compared in order to expedite continued assessment.