What is select fill?
Select fill is fill material that meets a specification, typically screened or imported granular soil with limited fines and no organics, chosen because it compacts predictably. Common fill is whatever suitable material is available, usually reused native soil.
The distinction is about risk. Under a lawn, common fill is fine. Under a slab, behind a retaining wall, in a utility trench under pavement, or anywhere settlement is expensive, specs call for material with known behavior: select fill, screened topsoil's opposite number, often a sandy or gravelly soil, DGA, or bank-run gravel depending on the spec.
What disqualifies material
- Organics: topsoil, roots, and anything that rots and leaves voids
- Construction debris, frozen chunks, and oversized rock
- High-plasticity clay that swells and shrinks with moisture
- Anything too wet to compact near optimum moisture
The cost conversation
Select fill is bought, trucked, and placed, so it costs multiples of reusing spoil. When a customer asks why the trench can't just be filled with "the dirt that came out," the honest answer is: it can, everywhere that settling doesn't matter. Where it does, the imported material is cheaper than the callback.