Piezometers

Applications

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 is the most basic of piezometer types. It consists of a filter tip joined to a riser pipe. Water flow from the surrounding soil into the standpipe. Readings are obtained with a water level indicator.

• Advantages: Simple, reliable, 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.

Vibrating Wire Piezometers

The vibrating wire piezometer is the most commonly deployed piezometer and is suitable for almost all applications. It 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.

Titanium Pressure Transducer

The titanium pressure transducer is a 4-20mA device that is compatible with industrial data loggers. It is use for monitoring water levels in pumping wells and for monitoring pore-water pressure in environments that would corrode stainless steel.

• Advantages: Suitable for dynamic measurements, easy to read, highly resistant to electrical noise.
• Limitations: 4-20mA circuits require more power so are less suitable for battery-operation. Long term stability may not be good enough for some applications.

Pneumatic Piezometers

The pneumatic piezometer operates by gas pressure. It 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.

Comparison of Piezometers