Performance of time domain reflectometers installed on a centrifuge

Time domain reflectometry (TDR) offers a diverse monitoring tool for physical soil models, particularly for tracking multiple fault locations along a single embedded sensor. This paper compares the performance of two TDR systems for use in geotechnical centrifuge experiments. The spatial resolution and sensitivity of two different reflectometers (Tektronix 1502C and Campbell Scientific TDR 100) are investigated at 1-g and on a centrifuge up to 50-g. The influence of multiplexers (VAZEC TR 200 and SDMX 50) on signal quality is quantified and discussed. Six different coaxial cable sensors are evaluated in the centrifuge, including four prototype sensors that are being created and tested for their capacity to detect shear zones in soils. According to experiments conducted at 1-g and in a centrifuge, the Tektronix system consistently provides a higher spatial resolution and sensitivity. Multiplexing sensors at any gravitational level, however, increases the signal rise-time such that spatial resolution and sensitivity are reduced. With proper set-up, both TDR systems can be securely employed in centrifuge tests, and relatively low centrifugal forces do not affect their operation. Voltage signals acquired at high g-levels are identical to those acquired at 1-g for five of the six cable sensors.