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My pier is mounted on a 1.3 M cube of concrete
http://www.iceinspace.com.au/forum/showthread.php?t=135400
and is surrounded by a 100 mm thick re-enforced concrete floor, underlain by a plastic impervious membrane, the observatory is mounted on this floor. The 20mm gap surrounding the pier I filled with spray in polystyrene foam.
http://www.iceinspace.com.au/forum/showthread.php?t=136306
All this is on clay to unknown depth (10-20 M?). The pier cube extends well below annual wet/dry zone into the permanently wet zone.
The surrounding floor was laid in summer with its top flush with that of the central cube. For the sake of comfort the observatory floor is covered in 19 mm thick interlocking foam tiles.
After the commencement of rain this season if noticed that the southern side of the floor was 8 mm higher than the cube, the north side was still flush.
So the wet/dry zone beneath the floor had become saturated and had swollen. OK, the floor had enough reo not to crack and the out of level does not effect the rotation of the dome, the central cube has not moved. Much more concerning was the discovery that the ground water was under sufficient pressure to penetrate through the spray in foam and pools of water collected under the foam tiles. This raises the humidity in the observatory. So this needs fixing.
Four hours with a penknife removed the top 50mm of the spray foam. Fortunately when I cast the floor I moulded in two outward sloping slots on the
western and northern side of the pier cube (one for future power entry and one for a dehumidifier drain line). So now ground water entering can exit via these channels. So that the floor tiles don't deform into the excavated slot I flattened some poly pipe and hammered it into the slot, water can flow beneath the pipe. Hopefully the pipe is flexible enough to still isolate the pier cube from floor vibrations. (There is still room for future power.)
This seems to work, no wet tiles, water leaving the northern drain this morning after rain last night, but for a belt and braces approach I placed another plastic membrane under the floor tiles.
Chris
