Considering Passive and Active Pressure on the wall
PROKON’s Retaining Wall Design module makes use of several general assumptions during the calculations, all of which are listed in the Help file (F1).
*Why do you get a different answer when reversing the direction of the same horizontal load?
The difference between the two results when the horizontal load is reversed can be attributed to the active and passive pressures.
The program assumes that the active pressure is predominantly applied from the right and passive pressure is predominantly applied from the left of the wall. Moreover, it assumes that the full passive pressure is generated and applied to the wall, regardless of the differences in soil height on either side of the wall. Consequently, the passive pressure, which in many cases is greater that the active pressure, dominates the movement of the wall.
The module automatically calculates the active and passive pressure coefficients, however, one can override these values, by using User Defined design values. If the active and passive pressure coefficient values are made equal and with no horizontal load applied, the pressure distribution underneath the wall will be equal, as show in the image below:
When considering an equal applied load due to the soil, the only effect on the wall is the applied horizontal load. In this case, reversing the load creates a mirrored pressure distribution as illustrated in the images below: