SLOPE INDICATOR - STANDPIPE PIEZOMETERS

Application

Standpipe piezometers are used to monitor piezometric water levels. Observation wells are used to monitor ground water levels. Water level readings are typically obtained with a water level indicator. Typical applications include:

• Monitoring pore-water pressure to determine the stability of slopes, embankments, and landfill dikes.

• Monitoring ground improvement techniques such as vertical drains, sand drains, and dynamic compaction.

• Monitoring dewatering schemes for excavations and underground openings.

• Monitoring seepage and ground water movement in embankments, landfill dikes, and dams.

• Monitoring water drawdown during pumping tests.

Installation

The standpipe piezometer, which is installed in a borehole, consists of a filter tip joined to a riser pipe. The filter tip is placed in a sand zone and a bentonite seal is placed above the sand to isolate the pore water pressure at the tip. The annular space between the riser pipe and the borehole is backfilled to the surface with a bentonite grout to prevent unwanted vertical migration of water. The riser pipe is terminated above ground level with a vented cap.

The observation well uses the same components as the standpipe piezometer, but is installed differently. No bentonite seals are placed and the borehole is backfilled with gravel or sand rather than a bentonite grout. The top of the borehole is sealed to prevent the entry of surface runoff, and the riser pipe is terminated above ground level.

Operation

Water levels in either the standpipe piezometer or the observation well are typically measured with a water level indicator. The 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. This is signaled by a light and a buzzer built into the cable reel. The depth-to-water reading is taken from the cable or tape.

• Economical components.
• Simple to read.
• Very good long-term reliability.