Terraced Retaining wall guidelines
It is essential that all retaining walls have the correct drainage system installed to prevent hydrostatic pressure issues.
Based on flat land behind the walls with no surcharges and flat land in front of the walls, the 2 to 1 terrace rule applies
That is the terrace width separating the 2 walls must be at least twice the height of the lower wall.
Should the separation be less than this, the two walls are deemed related, and the lower wall will need to be stronger to take the loads from the upper wall.