Volume 31, Issue 5 (September 2008)
A New Technique for Monitoring Movement of Buried Objects Using an Electrode Switching System
A novel technique for monitoring movement of buried objects using an electrode switching system is developed. The idea is to establish electromagnetic fields in a conductive medium by injecting low-frequency alternating currents through boundary electrodes. The movement of a buried object is related to the electrical potential measured on an electrode attached to it. A closed-form expression for potential distribution in a rectangular container is developed; boundary conditions are accounted for using a method of images. The resolution of spatial location using the proposed electro-location scheme is limited by the electrical noise and the accuracy of potential measurement, which depends on the excitation frequency, measurements per cycle of excitation, and samples per measurement. The tradeoff between spatial and temporal resolution is investigated. With appropriate sampling parameters, spatial and temporal resolutions of 1 mm and 1 ms have been demonstrated. The viability of the electro-location technique is demonstrated by measuring the liquefaction-induced settlements of heavy objects in the geotechnical centrifuge model test using an electrode switching system. The obtained positions agree remarkably with independent measurements. The electro-location method is considered to be a useful technique for monitoring subsurface movements in physical centrifuge models and has practical application potentials in the field.