I’m determining if a foundation for small tank requires piles or if a mat foundation is sufficient. I have an older geotec report in the vicinity that provides the allowable soil bearing pressure to stay under a specified settlement. This allows me to check the overturning resistance for wind and seismic. The report does not provide the lateral earth pressure coefficients (at rest, active, passive) nor does it provide an angle of friction. Is it possible to determine the active lateral earth pressure coefficient with only knowing the various soil types and how far below the surface they are? Are there conservative values that are acceptable for pressure coefficients? If the foundation is 14’wide x 14’long x 5’high can I compare the pressure on one side due shear from wind against the allowable soil pressure?
[Professional and Structural Engineer (ME, NH), American Concrete Industries, www.americanconcrete.com]
If it’s a buried tank you probably want the at-rest pressure coefficient. Ko = 0.5 is usually conservative and it’s what I usually design to if I have little to no info about the soils.
If sliding is a concern, then perhaps you’ll be developing the active soil pressure. Also, the Ko = 0.5 is quite conservative and you could lower it if you have a reasonable idea of the over-consolidation of the backfill.
In any case, you need a current geotechnical report to ensure nothing goes sideways on this job.
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