For tall walls design parameters of compaction and wall rock usage should be increased. Select/structural fill should be specified for the minimum bottom 1/3 to 1/2 of the reinforced fill. The use of additional select/structural fill should extend to the entire length of the reinforcement.
Also consider how much potential settlement will impact structures above the reinforced soil mass. For tall walls consider increasing compaction requirements from 95% to 98% of standard proctor to minimize settlement where essential to the application.
As walls get taller the internal stresses increase and depending on the soils used, can cause lateral loads pushing on the back of the facing. To minimize internal lateral loads on the Allan Block facing, it is recommended to expand the depth of the wall rock column behind the facing, See for more information.
In addition to the compaction and wall rock parameters, tall walls require the design engineer to evaluate the overall stability of the soil structure and the subsoils beneath the wall. The reinforced soil structure should be evaluated for internal settlement which may require additional select fill to mitigate. (ref. BP, Chapter 8.3)
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