It is often more aesthetically pleasing to replace one large retaining wall with two or more smaller terraced walls. Terraced walls can act as surcharges and may create global instability, therefore reinforcement may be necessary. Always check with a local qualified engineer when building terraces.
Retaining walls perform independently and may not need engineering when the distance between gravity walls is at least two times the height of the lower retaining wall, and the height of the upper retaining wall is equal to or less than the height of the lower retaining wall. Use the Gravity Wall Chart to determine if surcharges and may create global instability, therefore geogrid is required or check with a local wall engineer.
Retaining walls that must be evaluated by an engineer are any retaining walls needing geogrid reinforcement, retaining walls closer than two times the height of the lower retaining wall, retaining walls with more than two terraces, and terraced retaining walls with any structures above.
Terraced walls that do not perform independently must also be evaluated for global stability, and the lower walls must be designed to resist the load of the upper walls.