Soil and rock change volume when excavated (loose state) and when compacted (fill state). Bulking and shrinkage factors are critical for haul truck sizing, fill quantity, and cut/fill balance calculations. Bank volume = in-situ; Loose volume = after excavation; Compacted volume = after placement and rolling.
Compaction Factors (Bank → Compacted)
Compacted volume / Bank volume — useful for fill quantity from cut
| Soil Type | Bulking % | Shrink % | Loose Factor | Compact Factor | Note |
|---|
| Sand | — | — | — | 0.88–0.92 | Standard Proctor compaction |
| Loam / silty clay | — | — | — | 0.82–0.88 | — |
| Heavy clay | — | — | — | 0.78–0.85 | — |
| Black cotton | — | — | — | 0.75–0.80 | — |
| Murum / GSB | — | — | — | 0.85–0.90 | Pavement subbase |
| Gravel-sand | — | — | — | 0.88–0.93 | — |
Notes
• Bulking and shrinkage are SITE-DEPENDENT — measure on the actual material whenever possible
• Sand bulking is highest at 4–6% moisture content; collapses to nothing when fully saturated
• Always tender on Bank (in-situ) volume — payment by truckload (loose) leads to disputes
• For black cotton and other expansive soils, allow extra cut for the high shrinkage on compaction
• Re-using excavated soil as fill: assume 80% recovery for clays, 90% for sandy soils
• Hard rock blasting can give 50–80% bulking — pre-plan disposal volume accordingly
• When importing fill, specify the source — laterite, river sand, and crusher dust have very different compaction behaviour
• For pavement subbase (GSB / WMM), aim for 95–98% MDD compaction (max dry density)