that it will flow easily and not leave any air spaces.
3. Pour 1 liter of sand down the hole to provide a base for the sensor.
4. Lower the sensor until it reaches the bottom of the hole. A winch is required for deep
holes. In very deep holes it may not be obvious when the sensor has reached the
bottom. In this case, continue to lower the cable until it goes slack at the top end. (It will
eventually go slack because the cable is too stiff to fall down a narrow borehole, it will
stand wedged between the sides of the hole and not slide down more than a small
amount.) (See
"Lowering the Seismometer into a Deep Cased Hole" below
.)
5. Optionally, if you have serial communications to the sensor (a Centaur digitizer or SLIP
appliance is recommended for this), access the
State of Health
page and verify that
the case tilt is within the leveling range of the instrument. If not, it may be possible to
correct this by pulling up on the cable to move the seismometer around, and if need be,
maintain some tension on the cable while sand is poured down to stabilize it. If
excessive tilt cannot be corrected, it is likely because the hole is non-vertical at the
bottom end.
6. Pour a measured volume of sand down the hole, sufficient to cover the sides plus
15 cm (6 inches) on top. This is enough to stabilize the sensor, while still allowing it to be
easily extracted if necessary.
7. Slacken the cable.
8. Verify that the installation is level by checking that the mass positions are within an
acceptable range (at or very close to zero).
9. Optionally, in a shallow hole (less than 10 m depth) there may be a benefit to filling the
top end of the hole (from the top of the wellhead to slightly below ground level) with
insulating material such as bags of polyester wool to mitigate the effect of temperature
changes at surface.
10. Securely clamp the cable at the top end of the hole.
11. Close and seal the wellhead to prevent any water or moist air from entering the cased
hole.
2.7.3 Lowering the Seismometer into a Deep Cased Hole
Use the instructions in this section and Lifting Cable Kit (19251) to deploy the Trillium
Compact Posthole in a deep cased hole using a tripod and winch or another similar method.
Chapter 2 - Installing a Trillium Compact Posthole Seismometer
16889R10 • 2020-11-12
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