digester tank pad

huangyhg

digester tank pad
fellers,
i am designing a concrete base/pad for a 1.5 million pound digester that is 24' in diameter.  the tank is flat bottom bearing so it is about 3300 psf pressure.  we will have 3500 psf soil allowable.  what issues do i need to consider for designing the concrete pad since the pressure should be going straight thru
thanks

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if the pressure is uniform as stated, with well prepared, compacted fill, i don't see the need for concrete pad.
the pad is somewhat elevated from the surrounding level for containment issues so we must support directly on concrete and a stone base on compacted soil.
if the pad is larger than the tank, you should check shear and bending on the ledge as usual for all loads and load combinations, and provide reinforcing as required. if there are tie downs, check shear and pull out strengths. otherwise provide minimum reinforcement to maintain the connectivity (for local pockets due to soil errosion, uneven settlement...etc). make sure there is no ground water issues, and the runoff is draining away from the concrete pad.
have you checked the foundation for seismic?