Why Coulomb's Wedge Theory Ignores Earth Pressure at Rest

[whammy123]

Hi! Can someone tell me why Coulomb in his Wedge Theory of Earth Pessure didn't take into considertion Earth pressure at rest? He cosnidered only limit active and passive pressures, but why didn't he write anything about pressure at rest? I 've looked up some books, but there is only the derivation of formulas for active and passive pressure, without any note about pressure at rest. Thanks for help in advance!

 

[PhanthomJay]

It's been awhile since I have looked at my aging foundation texts, but it is true that 'at rest' lateral Earth pressure coefficients (k_o) are not given as much attention as 'active' (k_a) and 'passive' (k_p) lateral Earth pressure coefficients. For a non compacted dense sand (in place) with an angle of internal friction of 30 degrees, K_o is about 0.5, k_a = 0.33, and k_p =3.0. The respective Earth pressures are these coefficients times the vertical soil pressure at a given point. When a retaining wall or other foundation is subject to lateral loads, small deflections result in k_a and k_p governing, which is probably why you don't hear too much about k_o.