5
4. INSTALLATION
Before attempting an installation be sure that the filter stone is completely saturated (see Section
3) and that the space between the filter stone and the transducer diaphragm is filled with water.
Warning! Do not allow the piezometer to freeze once the filter stone has been saturated!
4.1 Establishing a Zero Pressure Reading
It is essential, in many cases, to establish an accurate zero pressure reading at the job site under
known conditions of barometric pressure and temperature. The following procedures are
important.
1)
Either remove the filter housing completely (preferred) or make sure that the filter stone is
saturated and that the space between the filter and transducer diaphragm is completely filled
with water.
2)
Lower the piezometer into the borehole or well until it is just above the water level.
3)
Allow 15 to 20 minutes for the temperature to stabilize before taking the reading.
4.2 Installation in Boreholes
Geokon piezometers can be installed in cased or uncased boreholes, in either single or multiple
piezometer configurations. If pore pressures in a particular zone are to be monitored, careful
attention must be paid to the borehole sealing technique.
The borehole should extend 6 to 12 inches below the proposed piezometer location. Boreholes
should be drilled without using drilling mud, or by using a material that degrades rapidly with
time, such as Revert
. Wash the borehole clean of drill cuttings. Backfill the borehole with
clean fine sand to a point six inches below the desired piezometer tip location. The piezometer
can then be lowered into position. (Preferably, the piezometer will be encapsulated in a canvas
bag containing clean, saturated sand.) While holding the instrument in position, (a mark on the
cable is helpful) fill the borehole with clean fine sand to a point six inches above the piezometer.
Three different methods of isolating the zone to be monitored are detailed below.
Installation A:
Immediately above the area filled with clean fine sand, known as the “collection zone”, the
borehole should be sealed by an impermeable bentonite cement grout mix, or with alternating
layers of bentonite and sand backfill, tamped in place for approximately one foot, followed by
common backfill. (See Figure 2.)
If multiple piezometers are to be used in a single hole, the bentonite and sand should be tamped
in place below and above the upper piezometers, as well as at interval between the piezometer
zones. When using tamping tools special care should be taken to ensure that the piezometer cable
jackets are not cut during installation, as this could introduce a possible pressure leak in the
cable.
