Quote:
Originally Posted by Rocket49
Why do they bother to remove the metal tubes?
Seems to me that leaving the metal tubes in the soil wouldn't affect the structural integrity of the foundation.
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Because 120' long, 5-20' diameter tubes made of 3/4 steel aren't cheap?
They don't affect the integrity and won't hurt it if left in either because oxygen is what causes rust, not water. There is very little oxygen dozens of feet below grade in Chicago hardpan which is why wooden pilings are pulled out of it all the time after 100+ years of being saturated by water.
The cassion is actually not the pier. The cassion is the sleeve itself and is a term for an underground coffer dam sunk to create a below grade space for foundation works like piers to be completed. The pier consisting of a rebar cage surrounded by a corrected metal sleeve filled with concrete is designed to be permanent while the cassion sleeve is yanked and the gap between them (now between the clay and corregated liner) is backfilled with gravel.
If I had to guess each section of cassion sleeve probably costs high 5 figures, maybe low six figures. The corregated liners can't be more than maybe $10 or $15k. it would add millions in construction costs to abandon a sleeve in each hole in a project like this which has dozens of cassions that need to be drilled.
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