A standpipe typically comprises a plastic pipe with perforations at its base, surrounded by a gravel or sand backfill. This configuration allows it to measure the water level within a specific area.
Conversely, a standpipe piezometer is a specialized instrument used to measure pore water pressure at a particular depth. It consists of a non-perforated plastic pipe with a perforated tip. The annular space around the tip is packed with sand, while the rest of the pipe is surrounded by a cement/bentonite grout seal. This isolation ensures that only the water pressure at the tip’s location is measured.
Essentially, standpipe piezometers are deployed to investigate pore water pressure variations at specific depths underground. However, as noted by Marius Tremblay (1989), their response time can be sluggish in clayey soils due to the low permeability of clay, hindering the rapid equilibration of water pressure within the piezometer.