9.6.2 Initial Stress Ratio

The initial state of stress in the soil can be characterized by the volumetric weight of the soil $\gamma$ , the depth z and the lateral pressure ratio K₀ . This ratio is defined as the quotient of the horizontal (principle) effective stress $\sigma^{{\prime}}_{{1}}$ and the vertical effective stress $\sigma^{{\prime}}_{{3}}$ :

$${\frac{{\sigma ^{\prime}_{1}}}{{\sigma ^{\prime}_{3}}}} {\frac{{\sigma ^{\prime}_{1}}}{{\gamma_{z}}}} \sigma^{{\prime}}_{{\mathrm{h}}} \sigma^{{\prime}}_{{\mathrm{v}}}$$ (9.5)

During the evaluation of the initial state for the nonlinear analysis, DIANA will compose the initial nonlinear stress components from the calculated elastic vertical stress of the specified load set and multiplication factor [Vol. Analysis Procedures].

The linear load set must contain a dead weight load from which DIANA derives the (vertical) direction of gravity.

For an isotropic material, a single K₀ value applies for all horizontal directions. For an orthotropic material, two K₀ values apply for two perpendicular horizontal directions.

Isotropic    (syntax)

K0

k0 is the pore pressure ratio K₀ , valid in all horizontal directions.

Orthotropic    (syntax)

K0

k0a and k0b are the pore pressure ratio's K₀ in two mutually perpendicular directions of a three-dimensional model with solid elements.

K0DIR

dira is a number referring to a direction in table 'DIRECT' [Vol. Analysis Procedures]. The horizontal component of this direction defines the actual direction for k0a. Therefore, the direction as specified in table 'DIRECT' must have a horizontal component, i.e., it may not coincide with the direction of the gravity acceleration.