"K" and relation to lateral pressure

[ToadJones]

Preface: I don't do much work with soils other than to find the necessary info from geotech reports.

Question I have is, in trying to determine embedment depths of pole type foundations the soil borings show soils at varying depths as having different pressure coefficients.
In determining the lateral earth pressures at the depths where the soils change, do you simply maintain the same pressure at the interface from the upper layer of the two soils and continue with a linearly varying pressure for the next layer? ...so on and so forth?

 

[FixedEarth]

The K values ou are referring to may be for driven piles. (Are the K values between 0.7 and 1.5?) The k for earth pressure is the ratio of lateral stress to vertical stress. So if K =0.33, then lateral stress is 33% of the vertical stress. Vertical stress is the soils unit weight times embedment depth, assuming no ground water.

For pole foundations, you are looking for the passive resistance which is equal to Kp x Gamma / FS. Kp is the inverse of K. Factor of Safety, FS, of usually 1.3 to 1.8 is applied so as to reduce the ultimate passive resistance to an allowable passive values.