Time dependence of lateral earth pressure

Both theoretical analysis and laboratory test data indicate that for normally consolidated soft clays the coefficient of lateral earth pressure at rest, K_o, gradually increases with time. Physical reasonining suggests that for all soils K_o should asymptotically approach unity. This reasoning implies that for overconsolidated soils with initial values of K_o greater than one, K_o should decrease with time. The time dependence of K_o has significant implications with respect to how the value of K_o measured in laboratory tests relates to in-situ values of K_o.