Define Soil Properties

Users can define a list of Soil Properties to use throughout the model. To open the Define Soil Properties dialog:

1. Select Soil > Soil Conditions > Define Soil Properties

Unit weight

The unit weight of the soil. If a saturated unit weight is defined, then this is the moist unit weight of the soil.

Saturated unit weight

If this is toggled on, then you can specify a different unit weight to use when the soil is below the water table. Note that this value corresponds to total stress (effective stress is calculated by subtracting the water unit weight).

Friction angle

The Mohr-Coulomb angle of friction that defines the shearing failure plane intrinsic to the soil.

Interface friction angle

The angle of friction to use whenever the soil is in contact with the wall or wall components.

Long-term cohesion

The long-term value of cohesion that can reasonably be expected throughout the lifetime of the structure. Note that using a value that is too high here will result in an unconservative analysis.

Coefficient of adhesion

If applicable, you can define an adhesion strength as a ratio of the cohesion (from 0 to 1) specific to where the soil touches the wall or wall components.

Seismic undrained behavior

This assumption affects the lateral earth forces during seismic analysis.. If seismic analysis is activated, you can select whether the soil is considered to be unconfined or confined during seismic shaking.

• Unconfined: The porewater moves independently from the soil structure and acts separately from the soil. During calculation of lateral earth pressures, typically an effective stress analysis is conducted, and then an additional hydrodynamic force is added separately using some form of the Westergaard equation (see below). Static hydrodynamic forces are calculated normally.
  
  where P_wd is the hydrodynamic force acting at a distance 0.4H above the base, k_h is the seismic horizontal acceleration coefficient, γ_w is the unit weight of water, and H_w is the height of water above the base.
• Confined: The porewater moves together with the soil. During calculation of lateral earth pressures, no additional hydrodynamic force is assumed. In some design standards such as AASHTO, a total stress analysis is conducted which includes both the hydrostatic and earth pressure forces.

Fill Condition

If the Australian Standard is selected, then the Fill Condition needs to be defined for each soil as it will affect the reduction factors of the friction angle and permanent cohesion values. The soil can be Fill condition can be classified as:

• Class I
• Class II
• Uncontrolled
• In Situ

Depending on the selection, the reduction factors will be selected from the tables in Section 5 in the AS 4678:2002 design standard.