In digging the foundation, our high retaining walls need a thicker and bigger footing to be able to resist the overturning pressure of the ground at street level. Additionally the amount of rebar in the footing has to be considerably more to add the extra strength that the high wall needs. This created a little challenge for us in the foundation drainage on the exterior wall, since the footing for the high walls were dug 6 inches deeper than the shallow walls. This difference had to be made up before the foundation drainage was put in.
It is amazing how much concrete and steel is needed to retain a wall where the ground is able to maintain a slope of 1 to 1 without any wall. The wall also needs to resist the added pressure of vehicle traffic when the wall is on the roadway. After the foundation is poured the retaining wall needs to be formed and then poured. Again the retaining wall needs a lot of rebar to resist the overturning pressure of the ground that pushes against it.