AASHTO T 252-96 (2004)

The principal reasons for measuring pore pressures in highway construction are: 1. to monitor strength increases during construction, 2. to estimate remaining settlements after construction, and 3. to determine existing pore pressures in landslides. This method consists of installing the pore water pressure measuring device in a soil layer at a point determined by detailed knowledge of the field conditions and theoretical evaluation of the need required. Pore pressure measurement may be made by determining the total pore pressure at the point or determining the differential pore pressure at that point relative to the surrounding normal ground water table. The data is usually reduced to "excess" pore pressure, which is the difference between the measured pore pressure and the "normal" pore pressure under the general ground water table for the area at the time of reading. Interpretation of pore pressure measurements in the field are complicated by the variability both vertically and horizontally in the soils. Therefore, interpretation of any pore pressure measurement can be misleading if the complete soil profile, loading history, and detailed soil parameters are not adequately known.