1.0 General Guidelines – Primary Backfill
1.1. The backfill supporting an underground storage tank is vital for a proper
installation.
1.2. Use rounded or crushed stone as specified in the Fiberglass Tank solutions
(FTS) Installation Manual and in this document. Note the following:
- Using non-specified material can result in voids and/or poor compaction.
- Using non-specified material will void FTS’s obligations on any warranty
claim. - The specified materials are a commonly available materials and are very
similar to the requirements for concrete aggregate.
1.3. Backfill must be clean, free-flowing, well-graded material that is free of:
- Dirt, sand, large rocks
- Organic material, roots, debris
- Ice, snow, or anything frozen
1.4. The material must be hard and stable when wet or under load.
1.5. Avoid soft materials like soft limestone, sandstone, sea shells, and shale,
which break down over time.
2.0. Primary Backfill Materials
2.1. Use coarse aggregate (rounded or crushed stone) meeting FTS size
requirements. Refer to Figure 1-1 and Table 1-1.
2.2. For rounded stone: Use rounded particles sized from 1/8″ to 3/4″. It’s often
called “pea gravel,” “pea stone,” or “roofing gravel,” depending on the region.
2.3. For crushed stone, use angular crushed particles sized from 1/8″ to 1/2″.