Geosense VW PIEZOMETERS, Инструкция по эксплуатации

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Version 1.4 May 09
5.2 Preparation for Installation
Prior to installation of a piezometer it is essential to establish and confirm details of
the installation to be carried out. Some of the main considerations are listed below :-
1. Intended elevation and depth to Piezometer?
This can be calculated as either the depth below a known level ( ground level
for example ) or as the elevation with respect to a remote datum. For borehole
installations the final depth should be calculated and then the cable marked to
show the intended installed position.
For surface installations, a reference elevation can be created close to the final
position of the piezometer.
2. Borehole Installation type / Specification
Where a piezometer is to be installed in a borehole, is it to be pushed into the
base of the borehole, installed in a filter pocket, grouted into the borehole
without a filter or provided with a long filter for groundwater monitoring?
The most common type of piezometer installation is the filter pocket type where
the piezometer is used to register pressures from a specific sub-surface horizon
or strata.
The full length ( or observation well ) installation is probably the next most
common. It simply allows groundwater from any horizon to flow into the
borehole to be registered by the piezometer.
Where a rapid response is required from a saturated material with a low
permeability, the piezometer can be pushed into the undisturbed base of the
borehole to provide an intimate connection to the pore water pressure in a
particular horizon.
Some engineers consider that a fully grouted borehole ( using a Bentonite /
Cement mixture ) will allow the piezometer to detect and reflect the pore
pressure equally well. In this installation, the piezometer ( or string of
piezometers ) is suspended in the borehole and the borehole is backfilled with
liquid grout from the base upwards. In some respects, this could be considered
similar to the push-in type installation, where the grout mix reflects the
permeability of the surrounding strata. This approach is particularly
advantageous where more than one piezometer is to be installed in a single
borehole.
3. Surface Installation type / Specification
Where a piezometer is to be installed at surface level, is it to be pushed into a
pre-formed cylindrical pocket or installed in a small excavated pocket? ( These
installations would normally be covered by fill material and often compacted
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