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Published By Lankelma

Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.


Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 6


Vibrating wire piezometer


The vibrating wire piezometer (Figure 48) 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. They are easy to read and very accurate. The response of the instrument to changes in pore pressure is good in all soils. As the measurement is obtained in terms of frequency it can be transmitted over long cable lengths and the
readings can be readily automated. The instruments must be protected
from electrical transients.
Typical applications are for monitoring:

  • porewater pressures to determine safe rates of fill or excavation
  • porewater pressures to determine slope stability
  • effects of dewatering systems used for excavations
  • effects of ground improvement systems (eg vertical and sand drains)
  • pore pressures to check the performance of earth-fill dams and
  • pore pressures to check containment systems at landfills and tailings dams.

Grout-in method
  The piezometer is lowered to the specified depth in
the borehole. The borehole is then filled with a bentonite–cement grout.
This method is particularly useful when multi-point measurements are
required in a single borehole.
Sand filter method  The borehole is flushed with water and a sand
filter is placed around the piezometer which is positioned at the specified depth. A bentonite plug is formed at the top of the sand filter. The remainder of the borehole is then filled with a bentonite–cement grout.
Push-in method  The push-in piezometer is generally pushed into soft,
cohesive soil using CPT equipment. The piezometer must be monitored
during installation to ensure that it is not over-pressured as it is pushed in.
The vibrating wire piezometer converts water pressure to a frequency
signal via a diaphragm, a tensioned steel wire and an electromagnetic
coil. The piezometer is designed so that a change in pressure on the
diaphragm causes a change in tension of the wire. When excited by the
electromagnetic coil, the wire vibrates at its natural frequency. The
vibration of the wire in the proximity of the coil generates a frequency
signal that is transmitted to the readout device. The readout device
processes the signal, applies calibration factors, and displays a reading
in the required engineering unit. 

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