RST Instruments VW2100, Instruction Manual, Page: 22 / 34

VW2100 Vibrating Wire Piezometer
Instruction Manual
ELM0005P RST Instruments Ltd. Page 22
5.6 P
IEZOMETERS
D
RIVE
I
N
S
OFT
G
ROUND
RST Model VW2100-DP is designed to be pushed into place from the surface in soft
soil. For deeper installations where driving from the surface would not be possible,
the piezometer may be pushed into place from the bottom of a pre-drilled borehole.
The model VW2100-DP piezometer comes with an adapter fitting which can be
connected to AW, C
PT, 1” NPT, or 1-1/4” NPT threaded pipe or drill rod for pushing.
The drive rods are larger in diameter than the VW2100-DP and form an effective seal
above the piezometer. The drive rods are left in the ground with the piezometers and
can only be retrieved when and if the piezometer is recovered. Should other rods
need to be adapted to push the VW2100-DP piezometer in place, it is important to
ensure that the first 1.5 meters of these rod have a diameter which is larger than the
outside diameter of the VW2100 piezometer housing.
5.6.1 Installation
1
Total saturation of the VW2100-DP filter is necessary for accurate results. Refer
to Appendix C which outlines the steps required to saturate a drive point
piezometer filter.
2
Prepare the rods to be used downhole. Lay a sufficient number of rods for the
push side by side, alternating between male threaded and female threaded ends.
3
Thread the piezometer cable through the rods leaving a 0.5 m loop of extra cable
laying flat on the ground at each rod end.
4
Leave an 8-meter length of free cable extending beyond the lower extremity of
the first rod (assuming 3-meter rod lengths). This should provide sufficient slack
to allow easy manipulation of the rods as they are screwed together and pushed
into the drill hole.
5
Pull back the spare cable. Screw the lower rod onto the piezometer body. Use a
pipe sealing compound or Teflon tape on the threads to form a permanent seal
preventing pore-water from flowing into the rod string, thus causing delay
response.
6
Add on the required number of rods in sequence to reach the push point.
7
Connect the VW2106 readout unit to the VW2100-DP and start monitoring the
readings prior to pushing.
8
Push the piezometer into place while monitoring any pressure build-up at the tip.
Stop the driving and wait until the pressure dissipates should the pressure
exceed the working pressure range.
9
Complete the installation and ensure the cable leads are protected.