Category:621 Flowable Backfill
To backfill is to refill an excavated area, often with the same soil as was originally removed. Soil characteristics such as shrinkage and swell factors (The ratio of the quantity of excavated material to the quantity of embankment that can be constructed from the same material) are important in typical backfill situations. Flowable backfill is used when ordinary soil compaction is not practical.
Construction Inspection Guidelines for Sec 621
Description (for Sec 621.1)
This item of work is used to backfill structures in locations where ordinary compaction methods are not practical. When correctly placed it is very stable and does not settle over time.
Consistency (for Sec 621.3.1)
The test method in the Standard Specifications should be used as a guideline. The intent of the specification is to attain a consistency that will flow freely but that will also hold the solids in suspension during placement.
Construction Requirements (for Sec 621.4)
Vibrators should not be used on flowable backfill because they will cause the solids to settle out. The mix proportions should be adjusted to produce a consistency that will flow freely. Care should be taken to plug all outlets including any drainage structures.