Stability analysis for cantilever walls

Factors of Safety are presented in a table of the following form:-

FoS for toe Toe elev. for Strut force elev. = -2.00 FoS = 2.000 for F=1.000 --------------- ------------- ----------- Stage --- G.L. --- Strut Factor Moment Toe Wall Strut No. Act. Pass. Elev. of equilib. elev. Penetr force Safety at elev. -ation kN/m run 2 11.00 6.00 Cant. 2.553 -0.90 0.20 5.80 ----- Case A Case B Case C

Heading InterpretationG.L. Act. Ground level, active side, at this stage.

G.L. Pass. Ground level, passive side, at this stage.

Strut Elev. Not applicable. "Cant" indicates a cantilever wall (i.e. no strut).

FoS for toeCase Aelev. = xxxx Calculated Factor of Safety for the toe elevation given in the data under "Wall

Properties". If the FoS is not adequate at any stage, the wall should be made deeper.

Moment equilib. The elevation at which overturning momentsat elev. balance restoring moments for a cantilever wall.

Toe elev. for Case BFos = yyyyy Toe elevation required to achieve the Factor of Safety given in the data under

"Analysis Options".

Wall penetration Wall penetration below GL on the passive side (corresponding to the above toe elevation).

Strut force Case Cfor F = zzzzz Not applicable to cantilever walls.

For cantilever walls the program does two calculations :-A) Factor of safety for the given wall depth.B) Required wall depth for a given factor of safety, Fp, specified by the user.

The depth of the wall, either assumed (case A) or calculated (case B), is taken in all cases to include the extra depth required to generate reverse passive resistance at the toe of the wall. Thus no additional penetration should be added to these depths to achieve the corresponding factor of safety.

In WALLAP, the extra depth required to generate reverse passive resistance is actually calculated (using the same factor of safety) rather than estimated as a fixed percentage of the wall penetration.

The program may print the message:-

Conditions not suitable for factor of safety calculation

This may be because:-

(a) There is no nett overturning moment; the active pressures are small or zero, possibly due to the presence of cohesive soil.

(b) The wall is tending to move from right ("passive") to left ("active"). If you want to calculate the factor of safety under these conditions you would have to reverse the data.