Standpipe Piezometers (Divers)

The standpipe piezometer, sometimes called a Casagrande piezometer, consists of a filter tip joined to a riser pipe. The filter tip is made from polyethylene or porous stone and has 60 micron pores. The riser pipe is typically made from PVC plastic pipe.

After the filter tip and riser pipe are installed downhole, a sand filter zone is tremied into place around the filter tip. The top of the filter zone is sealed with bentonite to isolates the porewater at the tip. The annular space between the riser pipe and the borehole is backfilled to the surface with a bentonite grout to prevent vertical migration of water. The riser pipe is terminated above ground level with a vented cap.

Standpipe piezometers can be pushed into very soft soil. In this case, a steel well point is used instead of the filter tip, and steel pipe is used instead of plastic pipe.

An observation well also uses a filter tip, but there is no bentonite seal and the borehole is backfilled with gravel or sand rather than a bentonite grout. Since the filter tip is not isolated from vertical migration of water, this type of installation is useful for monitoring the general water level, but not porewater pressure.

Water levels in either the standpipe piezometer or the observation well are measured with a water level indicator. A water level indicator consists of a probe, a graduated cable or tape, and a cable reel with built-in electronics. The probe is lowered down the standpipe until it makes contact with water. Contact is signaled by a light and buzzer built into the cable reel.

The depth-to-water reading is taken from the cable or tape. A unique detection circuit combined with a sensitivity feature helps users obtain consistent measurements and eliminates false triggering in different well and water conditions.