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GEO5 software

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Setting initial stress with K0 procedure

Providing the initial geostatic stresses are derived using the K0 procedure, the GEO5 FEM program allows the user to take into consideration a potential preconsolidation of soils. The K0 procedure gives the current (initial) stress σz0. As an example we may consider only the selft weight of soils. As a next step we determine the transverse stress σx0.

In the case of normally consolidated soils we adopt the coefficient of lateral earth pressure at rest K0NC, which can be either inputted directly or determined from expressions defined separately for cohesive (, where ν is the Poisson ratio) and cohesionless (, where φ is the angle of internal friction) soils.

In the case of overconsolidated soils the transverse stress is determined with the help of overconsolidation parameters OCR or POP. These parameters may also serve to adjust the initial precosolidation pressure pc that appears in the formulation of material models with a compression cap. The specific preconsoldation parameter gives the way of determining the transverse stress σx0. In particular:

1) Using parameter OCR. This approach provides three options:

  • Input K0. This option is recommended providing a reliable value of the coefficient of lateral earth pressure at rest of an overconsolidated soil K0 is available. However, an inappropriate combination of parameters K0NC and OCR may generate an unallowable state of initial geostatic stress of an overconsoidated soil. Regardless of the selected material model it should generally hold that the mean stress σmpc pertinent to an original normally consolidated soil is greater than the mean stress of an overconsolidated soil σm0 corresponding to the state upon some sort of unloading. Owing to the fact that

the condition σmpc ≥ σm0 requires

Point out that violating this condition will have an impact on setting the preconsolidation pressure pc in models with the cap yield surface as well as on initialization of the Hypoplastic clay model. Further details can be found in the theoretical manual.

  • Calculation (ν). The value of parameter K0 is provided by

  • Calculation (α). The value of parameter K0 is provided by

where the value of α is typically set as α = 0.5 or α = sinφ. The value of transverse stress σx0 then follows from

2) Using parameter POP. In this case the value of transverse stress σx0 is given by

Further details can be found in the theoretical manual.

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