Determine and illustrate about the earth pressure at rest.

EARTH PRESSURE AT REST

You have seen that the active pressure is the minimum lateral pressure while the passive pressure is the maximum lateral pressure. Active pressure is associated with the expansion of the soil and the passive pressure with the compression of soil. In both the conditions the soil mass is in a state of incipient failure. The soil in its natural state at a depth z below the ground level is not subjected to any strain. The element is in a condition lu~lown as the "at rest" condition. The corresponding lateral pressure, called the earth pressure at rest is expressed in the form,

P₀ = K₀ σ_Z = K0 γ_Z   ........1

Where, K_O is termed as the coefficient of earth pressure at rest 0, is the effective vertical stress at depth z. At rest condition it also termed as K_O condition.

If the soil mass is considered to be semi-infinite, homogeneous, elastic and isotropic material, the magnitude of can be shown to be,

K = μ/(1-μ)   ..............2

Here μ is the Poisson's ratio of the material

For sands and normally consolidated clays, the magnitude of can be related to the θ value as follows:

K₀ = (1 - sin θ)   ...........3