Flat ribbon cable sensors for measurement of soil electrical conductivity using time domain reflectometry

Salt movement and accumulation within the subgrade, subbase or base materials of pavement is a major concern for practitioners and researches in the area of transportation geotechnics, essentially because it prompts damage to the thin bituminous surface layer causing weakening of bonding and cracking of the road surface. In this regard, the electrical conductivity (EC) of the pore water or saturated soil is a strong indicator of the salinity of the pavement materials. With this in view, this paper describes the electrical conductivity measurement using time domain reflectometry (TDR) employing flat ribbon cable (FRC) sensors of several lengths. This also enables a continuous measurement, and helps overcome the uncertainties associated with the point-wise measurements made by the conventional rod probe sensors. Calibration of the rod probe and the FRC sensors is depicted in detail in this paper, along with several calibration functions. It is expected from the study that the FRC sensors may particularly be useful in spatial monitoring of the state parameters of the soil along long sections of the pavement in a continuous and non-invasive manner.