Overlap locations of horizontal reinforcing bars in retaining walls should be carefully studied when the retaining wall is divided by edge columns connected to the retaining wall. This is due to the bending moments caused by the earth pressures applied on the retaining wall. On the other hand, if the wall is running without any edge columns, then the horizontal reinforcing bars are just added for shrinkage purpose. We’re showing an example of a retaining wall where the columns are acting as horizontal supports due to their rigidity for more clarity:

From this photo, bar overlaps should be at the mid span of the outer face of
retaining wall, and should be at the support location in the inner face of the retaining wall. The concept is very simple, follow the bending moment diagram 😉