How Many Samples of Cores Required for Compaction Test of Backfill?

An auditorium of size 42m x 25m is under construction, whose plinth is completed and backfilling is in process. The client has requested for compaction test of the backfill. The compaction test is carried out by the core cutting method. How many samples of Core Cut should be carried out to for determination of compaction of backfill? (Please support the answers with references)