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2. INSTALLATION PROCEDURES
Most installations are in fills and embankments where the sensor and cables are buried.
Elsewhere the cables and sensors may be attached directly to structures undergoing settlement of
heave. The reservoir location must always be at a higher elevation then the sensor and higher
than any part of the liquid filled connecting tube.
Prefilled systems are usually delivered with de-aired antifreeze solution already in the liquid
lines. An extra length of small diameter tubing is connected to the outer ends of the liquid lines
to allow the system to breath during transportation while simultaneously protecting the sensor
from being overranged by temperature or pressure fluctuations and preventing the entry of air
bubbles into the main liquid lines.
Alternatively, systems may be provided with the tubing empty for filling in the field.
2.1 Installing the Sensor
The sensor is usually attached to a settlement plate using the bracket(s) provided.
The settlement plate may be attached directly to a structure using bolts. In the case of installation
in fills, a smooth, flat bottomed excavation should be made about 300 to 600 mm (12 to 24")
deep. The sensor plate is placed on this flat surface and covered with fine material, similar to the
fill, with all particles over 10 mm (0.4") in size removed. This material should be tamped down
around the cell until the excavation is filled back to the original ground surface. The elevation of
the settlement plate should be measured at the time of the installation using conventional level
survey techniques. Check also that the sensor is still functioning after tamping.
2.2 Installing the Cables and Liquid Filled Tubes
Cables and tubing need to be placed in a trench approximately 300 to 600 mm (12 to 24") deep.
The trench should not undulate and individual cables and tubes should be laid side by side
without touching or crossing each other. In no place should the tubing be higher than the
reservoir location. Before backfilling the trench, examine the tubing for signs of air bubbles: If
any are noted, the tubing will need to be flushed before initial readings are taken.
Compact the material in the trench around the cables. Do not allow large angular pieces of rock
to rest directly on the cable. To prevent migration of water along the trench, bentonite plugs can
be constructed at intervals.
Trenches in earth dam embankments should never penetrate entirely through the clay core.
Compaction of the fill above the cables can proceed in a normal manner when the cover exceeds
600 mm (24") depth. Where cables are not buried, they should be adequately supported along
their length to prevent undulations. They should also be protected from direct sunlight and
insulated from rapid temperature fluctuations by encasing them in Styrofoam or urethane foam,
etc.
