Fill Materials: How do you identify Fill materials in the field?

Certainly! Identifying fill materials in the field is crucial during geotechnical investigations. Here are some key steps and indicators to help you identify fill materials:

1. **Aerial Imagery and Topo Maps**:
   1. Evaluate aerial imagery for evidence of fill piles, filled-in ponds, ravines, or low areas.
   2. Review topo maps for possible grading and grade changes.
   3. Prior borehole logs and geotechnical reports may contain evidence or notes related to fill or suspected fill.
2. **Construction Inspection Reports**:
   1. Records of deep foundations (such as piles, helical piers, or grade beams) can indicate looser or unconsolidated soils due to the presence of fill.
3. **On-Site Field Observations**:
   1. Look for evidence of unusual grading or built-up areas.
   2. Observe filled-in areas such as gullies, ravines, ponds, or former wetlands.
   3. Note grade changes and other constructed features like retaining walls.
   4. Ask locals, property owners, drillers, and contractors about their knowledge of area development and conditions.
4. **Geophysical Surveys**:
   1. Consider conducting a pre-drilling geophysical survey to identify fill materials or changes in soil type.
5. **Subsurface Investigation** (Drilling or Test Pit Excavation):
   1. Look for soft soils.
   2. Note low Standard Penetration Test (SPT) values (or 'N'-values).
   3. Pay attention to abrupt changes in 'N'-values during split-spoon sampling.
   4. Consult with the driller about their opinion based on how it "feels" while drilling (some drillers can sense if they are drilling through fill).
6. **Evidence of Buried Non-Native Materials**:
   1. If you encounter buried topsoil, significant rootlets at depth (not always), debris, pavement fragments, coal fragments, clinkers, or construction materials (glass, wood, bricks, metals), it's likely fill material.
   2. Consider how native soils are originally deposited (e.g., glacial deposition, sediment from water or wind) and compare it to the observed deposition.

Remember that identifying fill materials can be challenging even for experienced geotechnical professionals. Keep learning from field experience and continue refining your skills.