ABSTRACT
Electrical Resistance Tomography (ERT) was used to image spatial moisture distribution and movement in pavement sections during an infiltration test. ERT is a technique for determining the electrical resistivity distribution within a volume from measurement of injected currents and the resulting electrical potential distribution on the surface. The transfer resistance (ratio of potential to injected current) data are inverted using an algorithm based on a finite element forward solution which is iteratively adjusted in a least squares sense until the measured and calculated transfer resistances agree to within some predetermined value.
Four arrays of ERT electrodes were installed in vertical drill holes 1.22 m (4 ft) placed at the corners of a square 61 cm (2 ft) on a side into a pavement section which is used for a truck scale ramp on U.S. Highway 99 just north of Sacramento, CA. Water was introduced slowly into the pavement through a shallow hole in the center of this pattern and ERT data were collected in various planes as the water infiltrated into the pavement and subgrade materials over a period of several hours.
The ERT data were inverted, and the resulting images show 1) the basic structure of the pavement section and 2) the movement of water through the image planes as a function of time during infiltration. An interesting result is that the water does not appear to drain from the section toward the shoulder as had been expected based on the design.
