Application
Typical applications for piezometers are:
- Monitoring pore water pressures to determine safe rates of fill or excavation.
- Monitoring pore water pressures to evaluate slope stability.
- Monitoring dewatering systems used for excavations.
- Monitoring ground improvement systems, such as vertical drains and sand drains.
- Monitoring pore pressures to check the performance of earthfill dams and embankments.
- Monitoring pore pressures to check containment systems at landfills and tailings dams.
Types of Piezometers
Standpipe Piezometers
The standpipe piezometer, which is installed in a borehole, consists of a filter tip joined to a riser pipe. Readings are obtained with a water level indicator.
Advantages: Simple, reliable inexpensive, not electrical, no calibrated components.
Limitations: Accuracy depends on skill of operator; reading requires a man on site; remote reading not possible; slower to show changes in pore-water pressure.
Pneumatic Piezometers
The pneumatic piezometer consists of a pneumatic pressure transducer and pneumatic tubing. It can be installed in a borehole, embedded in fill, or suspended in a standpipe. Readings are obtained with a pneumatic indicator.
Advantages: Reliable, remote reading possible, not electrical, indicator can be calibrated at any time.
Limitations: Accuracy depends on skill of operator; difficult and expensive to automate, so reading requires man on site; reading time increases with length of tubing; pneumatic tubing can be blocked by condensation if not frequently charged with dry nitrogen gas.
Vibrating Wire Piezometers
The vibrating wire piezometer consists of a vibrating wire pressure transducer and signal cable. It can be installed in a borehole, embedded in fill, or suspended in a standpipe. Readings are obtained with a portable readout or a data logger.
Advantages: Easy to read, very accurate; good response time in all soils; easy to automate; reliable remote readings.
Limitations: Must be protected from electrical transients.
Multi-Level Vibrating Wire Piezometer
The multi-level VW piezometer system is used to monitor pore-water pressure at multiple zones in a borehole. It consists of a number of VW piezometers in special housings, signal cable, a grout fitting, and some user supplied components (mainly PVC pipe). The system is grouted into a borehole. Readings are obtained with a portable readout or a data logger.
Advantages: Solves or avoids most of the problems with traditional multi-level piezometer installations.
Limitations: Same as VW piezometers.
Vented Vibrating Wire Pressure Transducers
The vibrating wire piezometer consists of a vibrating wire pressure transducer, a vented signal cable, and a desiccant chamber. It is designed for monitoring water levels in wells, stilling basins, and wiers. Readings are obtained with a portable readout or a data logger.
Advantages: Easy to read, accurate, and can be connected to data loggers. Requires no barometric pressure compensation.
Limitations: Electrical noise from a pump in the same well can interfere with operation.
