When a rigid concrete retaining wall is to be used, the designer must consider that
such a wall can tolerate only minimal differential settlement. If differential settlement
is predicted, the designer may have to accommodate this situation by vertical joints in
the wall and other systems of articulation in the wall. In many instances, this type of
wall, under situations where differential or excessive settlement is anticipated, will
require deep foundations such as caissons or piling driven to firm supporting material.
Alternatively, subexcavation and replacement of poor material at the base of the wall
may be appropriate. When a mechanically stabilized wall is selected under conditions
of poor foundation soils, the wall is more tolerant to such a foundation condition. It is
important for the owner to realize that while the wall is more tolerant to this condition,
the end result as viewed from the finished top surface of the wall may be decidedly
different. Therefore, it is important for the owner to set out the requirements of, and
acceptance criteria for, the wall prior to the selection process. All alternative wall
types evaluated should meet those criteria. Otherwise, the owner is not evaluating
equal alternatives