7 installing in post-holes – Guralp Systems CMG-3ESPCD User Manual
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CMG-3ESPCD Digital Broadband Seismometer
Installing the 3ESPCD
7. Carry on removing soil, either with your hands or (very carefully!) with
the shovel, until the whole bag is uncovered to about half the height of
the instrument.
8. If the hole is relatively dry, open the bag and lift the instrument out by
its handle.
Caution: Do not lift the instrument by any of the attached
cables. Straining the cables may result in invisible damage,
making future installations unreliable.
9. Alternatively, if the hole is waterlogged, carefully lift out the entire bag
in one piece, and remove the contents at the surface.
3.7
Installing in post-holes
The 3ESPCD is suitable for installation in potholes. In soft subsoil, a hole 2 –
4 metres deep and 20 cm wide can be conveniently excavated using a
tractor-mounted or hand-operated pothole auger. To minimize surface effects,
you should ensure that the hole is at least 1 metre deeper than the length of
the instrument, and preferably somewhat more.
Since the hole has no lining, it may occasionally flood. However, most soil
types are sufficiently permeable to allow water to soak away, leaving the
packing material moist.
To install a 3ESPCD in a pothole:
1. Clean the pothole, making sure there is no loose material around the
mouth of the hole or on its base.
2. Prepare the instrument package, making sure the inclinometer is
visible, and attach it to a winch or hoist by clamping a light steel cable
to the centre of the handle so that the package hangs vertically.
Connect the signal cable to the instrument.
3. Add packing material to the hole to about 15 cm depth. Fine crushed
rock, with a high proportion of rock flour and fine particles, makes
excellent packing material. Alternatively, a mixture of 3 mm grade
angular coarse grit with around 30% medium grit gives good results.
Moisten the packing material in the hole and ram firm.
4. Lower the instrument to the bottom of the hole, but without slackening
the lifting cable.
5. Fill more packing material around the instrument for about 30 cm,
moisten, and ram firm.
6. Use the bubble level to check that the instrument remains within its tilt
tolerance (± 2 °).
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Issue B - November 2013