16
5.6
Gravel specification
Primary backfill specification:
•
Primary backfill material should be free-flowing granular material.
•
Compaction should be by lightweight rollers or vibratory plate. Compact gravel evenly
to ensure proper support for the tank. Make sure the vibrating machine does not come
in contact with the shell of the tank.
•
Tanks installations require primary backfill only within the region immediately
surrounding the tanks. This backfill must extend a minimum of 250mm outward from the
tank, and directly beneath the tank.
•
Backfill material shall not be frozen or contain lumps of frozen material at any time during
installation.
•
Use of other than specified backfill and bedding materials will void the tank warranty.
The following materials are approved as primary backfill:
Rounded pea gravel:
•
Minimum particle size 3mm, maximum 18 mm, compacted to a relative density of
>70%.
•
Gravel shall be clean and free flowing, free from large rocks, dirt, sand, roots, organic
materials or debris.
•
Upon screening analysis, the backfill material shall have no more than 5% by weight
passing 2.36 mm sieve.
Or
Crushed or processed stone:
•
Minimum particle size 3 mm, maximum 12 mm, compacted to a relative density of
>40%.
•
Dry gravel density must be at least 1500 kg/m3. The material should be washed or screened
to remove fine particles.
•
Upon screening analysis, the backfill material shall have no more than 5% by weight
passing a 2.36 mm sieve.
Pea Gravel
Crushed Stone
