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GEO5

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Ko Procedure

Ko procedure is the method that allows for the calculation of geostatic stress (1st stage) when particular ration between vertical and horizontal stress components is needed. For example, when dealing with overconsolidated soils the actual horizontal stress can attain much higher values than found in normally consolidated soils.

When adopting standard analysis the initial stress is determined through the application of the finite element method. Nonlinear material models can be used to account for evolution of possible failure surfaces already in the 1st calculation stage. In the case of elastic response the ratio between vertical σz and horizontal σx stress components is provided by:

where:

σz

-

vertical normal stress

σx

-

horizontal normal stress

ν

-

Poisson's ratio

This analysis may lead to evolution of plastic strains.

The Ko procedure generates only elastic response. The horizontal stress in the 1st stage of construction follows from:

where:

Ko

-

coefficient of horizontal stress at reast defined by the user

σz

-

vertical normal stress

σx

-

horizontal normal stress

The Ko coefficient is assumed to be a soil parameter. If the Ko parameter is not assigned, it is derived from the relation:

The resulting stresses may, however, violate the plasticity condition in the 2nd stage of construction when nonlinear material models are used. Iteration of equilibrium is then carried out even if no changes occur in the 2nd stage.