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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.
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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.
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