Overturning (Retaining Wall)

Last modified by Fredrik Lagerström on 2021/06/29 15:54

The program displays a warning as soon as the plate lifts from the ground. This is however not the upper limit for allowed eccentricity except for rock where the plate is not allowed to lift.

An overturning check should be made according to [1]

The design case EQU is used to check overturning.

  • Edst,d < Estb;d + Td
    • Edst,d is the design value for the effect of overturning loads,
    • Estb,d is the design value for stabilizing loads,
    • Td is mobilized shear force under the plate (normally of minor importance)

The loads are then to be determined for the design case EQU meaning load equation 6.10a according to EN 1990. The belonging load partial coefficients are to be found in EN 1997-1-1 Annex A table A1and material partial coefficients in table A2. This mean that favorable permanent loads get a factor 0,9 and unfavorable loads a factor 1,5. It is important that these factors are a part of the calculation! This would mean an overturning security of minimum 1,67.

It is especially important to perform the overturning check if the eccentricity is larger than 1/3 of the plate width but according to [1] static equilibrium EQU will normally in geotechnical design be limited to rare cases such as rigid foundation bearing on rock or soil with very high bearing resistance where the overturning axis will be situated at or very near the plate edge.

According to [1] 6.5.4 in the case that the eccentricity is larger than 1/3 of the plate width special precautions are to be taken as shown below and the program will display a warning in this case.

Careful review of the design values of actions with [1] 2.4.2.

Designing the location of the foundation edge by taking into account the magnitude of construction tolerances.

Unless special care is taken during the works, tolerances up to 0,10 m should be considered.

Normally the risk for overturning is limited when one of the following conditions is fulfilled:

The load eccentricity is less than 1/3 of the plate width.

The bearing capacity is adequate. (As mentioned above overturning is primarily possible for soil with very high bearing resistance).