"The Proctor Compaction Test establishes the maximum unit weight that a particular type of soil can be compacted to using a controlled compactive force at an op

"The Proctor Compaction Test establishes the maximum unit weight that a particular type of soil can be compacted to using a controlled compactive force at an optimum water content." That looks like geotechnics to me (UK). It's also not too useful here. Compacting soil is for certain parts of paths and roads construction, not retaining walls.