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5. Installation Procedure
5.1 Installation in Standpipes
To install the piezometer in open standpipes the transducer is normally lowered to the surface of
the water and slightly immersed to allow the unit to come to thermal equilibrium (approximately 5
minutes). A zero reading is taken and the piezometer can then be lowered to the desired position in
the standpipe.
In situations where packers are used in standpipes the same sequence as above should be noted
and special care should be taken to avoid cutting the cable jacket with the packer since this could
introduce a possible pressure leakage path or short circuit the instrument.
5.2 Installation in Boreholes (traditional sand layer method)
HMA Geotechnical piezometers can be installed in boreholes in either cased or uncased holes.
Careful attention must be paid to borehole sealing techniques if pore pressures in a particular zone
are to be monitored.
Boreholes should be drilled either without drilling mud or with a material that degrades rapidly
with time, such as Revert. The hole should extend from 150 to 300mm below the proposed
piezometer location and should be washed clean of drill cuttings.
The bottom of the borehole should then be back filled with clean sand to a point 150mm below the
desired piezometer tip location.
The piezometer can then be installed, as delivered, or preferably encapsulated in a filter cloth bag
containing clean, saturated sand.
It is then lowered to the surface of the water and slightly immersed to allow the unit to come to
thermal equilibrium (approximately 5 minutes). A zero reading is taken and the piezometer can
then be lowered to the desired position in the borehole.
While holding the instrument in position (a mark on the cable is helpful) clean sand should be
placed around the piezometer and to a point 150mm above it.
Immediately above the collection zone the borehole should be sealed with either alternating layers
of bentonite and sand back fill tamped in place for approximately 300mm followed by common
back fill or by an impermeable bentonite –cement grout mix.
If multiple piezometers are to be used in a single hole, the bentonite-sand plugs should be tamped
in place below and above the upper piezometers and also at intervals between the piezometer
zones. When designing and using tamping tools, special care should be taken to ensure that the
piezometer cable jackets are not cut during installation.
It should be noted that as the vibrating wire piezometer is basically a no flow instrument, collection
zones of appreciable size are not required and the piezometer can in fact, be placed directly into
most materials provided that the fines are not able to migrate through the filter.
