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Re: Self Driving Caissons

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I use the term "sunk caisson method" in lieu of self-driving caisson.  I've
designed some circular pump stations installed as sunk caissons -
approximately 40-ft in diameter and 50-ft deep; walls were up to 3.5-ft
soils were mostly clays.  The structure should be designed for tilting
sinking and uneven soil pressures - but the magnitude of loads is somewhat
judgement.  (I arbitrarily assumed 50% of the projected lateral soil
applied as a point load on two sides of the cylinder to get bending stresses
in the circular walls.)  I also designed for full internal fluid pressure
neglecting external soil pressure (walls in circular tension) and for full
external soil pressure (walls in compression, including consideration of
buckling), as well as for vertical bending stresses based on PCA tables for
circular tanks.

I recently designed a rectangular pump station assuming cast-in-place
construction in a braced excavation - but the contractor bid an alternate
using the sunk caisson method.  The alternate design submittal is due in
month, and I am looking forward to seeing how the contractor designed it,
since I felt this method was not practical for a large rectangular structure
(approx. 40-ft square by 50-ft deep, with wet and dry pits interior).