8.83. Underground piping must be backfilled with one of the materials referred to in section 8.82 in such manner that(1) the piping is bedded on at least 150 mm of backfill;
(2) there is at least 150 mm of backfill measured horizontally between the piping and the excavation wall;
(3) the backfill between each pipe is at least twice as thick as the nominal diameter of the largest pipe; and
(4) the backfill above the piping is at least 450 mm deep including the finishing grade layer.