The stress state existing in a point of the soil depends on its self-weight, stress history, groundwater conditions, and external loads applied to it. The application allows determining the vertical stresses due to self-weight.
Knowledge of these stresses, defined as geostatic, is of great importance for a correct interpretation of in-situ tests, laboratory tests, and also when in practice limit analysis is used to solve stability problems.
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A simple case is that of a soil bounded by a horizontal surface: in this situation:
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every vertical section can be considered as symmetric, there are no shear stresses on vertical and horizontal planes;
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the vertical σvo and horizontal σho stresses are principal stresses;
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the total vertical stress σvo at a generic depth z is simply given, in the case of a homogeneous soil with a total unit weight equal to γ, by the relation:
σvo=γ·z
and, in the case of stratified soil:
σ’vo=Σγi·zi
– the effective vertical stress σ’vo is calculated, once the groundwater conditions are known and therefore the value of the water pressure uo is known, from the following relation:σ’vo=σvo-uo