Guralp Systems CMG-6TD User Manual
Page 24
Installing the 6TD
1. Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to
the bedrock if possible.
2. On granite or other hard bedrock, use an angle grinder to plane off the
bedrock at the pit bottom so that it is flat and level. Stand the
instrument directly on the bedrock, and go to step 7.
3. On soft bedrock or subsoil, you should install a pier as depicted below.
4. Pour a layer of loose, fine sand into the pit to cover the base. The type
of sand used for children's sand-pits is ideal, since the grains are clean,
dry and within a small size range. On top of the sand, place a smooth,
flat granite plinth around 20 cm across, and shift it to compact the sand
and provide a near-level surface.
Placing a granite plinth on a sand layer increases the contact between
the ground and the plinth, and improves the performance of the
instrument. There is also no need to mix concrete or to wait for it to
set.
5. Alternatively, if time allows and granite is not available, prepare a
concrete mix with sand and fine grit, and pour it into the hole. Agitate
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Issue F - February 2014