what sort of soil pressure checks do i need to do for footin
 

what sort of soil pressure checks do i need to do for footin
hi, everyone. i am designing a silo footing, say 18 ft x 18 ft, and 2 foot thick. there is a 58 foot tall silo on my footing. forces acting on my footing include the dead and live loads of the silo. i have wind and seismic loads on my silo, too, resulting in base shear and overturning moments on my footing.
i am checking the adequacy of the footing, and so far have checked stability and sliding. f.s. for stability is >1.5 and for sliding is >2, so both are ok.
my question is what sort of soil pressure checks do i need to do on my footing? what load cases do i need to consider? so far, i have checked dl + ll. i understand i need to do dl + wl, and dl + eq, too, is that correct?
also, what is the purpose of calculating the eccentricity, e, locating the kern, and then finding the values for the coefficients c1 and c2?
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1. correct. i re
the first thing you need when designing a footing is an allowable soil pressure. this is typically where the geotechnical engineer comes in. unless you have an extensive background designing footings in a particular area, you should contact a local geotech to do a boring or two and get you that info.
the eccentricity (m/p) will determine the soil pressure distribution under the footing.
if e =m/p <l/6, the soil pressure is trapezoidal.
if e =m/p =l/6, the soil pressure is triangular
if e >l/6, the soil pressure is triangular
get a good structural concrete textbook and look up footings under eccentric column loads.

thank you.
all load combinations shown in asce 7-05, (chapter 2), must be checked for each component of the structure. "0.6d + w + h" may control for soil/footing design.