The backfill material used was locally available poorly graded dry
sand. The maximum and minimum dry unit weights for the sand
were reported as 17.66 and 14:03 kN∕m3, respectively, and the
specific gravity of the sand was determined as 2.64. To achieve
uniform density, sand was placed in the perspex box using the pluviation (raining) technique. The average unit weight and relative
density achieved were within the range of 16:08–16:20 kN∕m3 and
62–65%, respectively, for the same height of fall. Other index properties
were reported as per Indian Standard (IS: 2720 are shown in
Table 1.