Passive wireless sensors for monitoring particle movement at soil-structure interfaces

Abstract

The load transfer and shaft capacities of civil infrastructure foundations (e.g., axially-loaded piles) depend on the soilstructure interface's shear and friction interactions. However, cyclic loading (e.g., ground motion) can dramatically deteriorate the shaft resistance of these foundations leading to catastrophic structural failure, thereby motivating research in understanding mechanics, soil-structure interactions, and interface responses. While tethered sensing systems have been adopted for gaining insight on soil-structure interfaces, the cables that interconnect sensors with the data acquisition system can interfere with measurement of true soil-structure response. Thus, the objective of this study is to develop a passive wireless sensor that is capable of measuring absolute displacement of soil particles at the soil-structure interface. Wireless communications and power transmission to the sensor is accomplished via electromagnetic coupling between a portable reader and sensor tag. Here, the reader is simply a coil antenna connected to an impedance analyzer, and the sensor circuitry comprises of a resistor, inductor (i.e., coil antenna), and capacitor connected in a series configuration. The displacement of the embedded sensor can be easily measured by correlating reader impedance changes with the reader-to-sensor's line-of-sight distances. Preliminary experimental results of the passive wireless sensor's displacement measurement capabilities are presented.